He that takes medicine and neglects diet wastes the skills of the physician.
A few short decades ago, scientific communities viewed vegan diets as downright dangerous, and health practitioners warned against their use. Gradually, research studies provided compelling evidence for their safety, and attitudes began to shift. Today, the views of the medical establishment are clearly reflected in the official position of the Academy of Nutrition and Dietetics (formerly the American Dietetic Association): “It is the position of the American Dietetic Association that appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases.”1
Vegan diets have not only been vindicated, but they’re also being hailed as health heroes, and for good reason. They provide a simple solution for the global epidemic of chronic disease. Well-designed vegan diets afford powerful protection against an imposing list of noncommunicable diseases and serve as safe, economical, and highly effective treatment tools.
The primary criticism leveled against vegan diets is that they’re nutritionally inadequate and that, relative to non-vegan diets, they increase the risk of malnutrition. People assume meat is necessary for protein, iron, and zinc, and dairy products are required to meet calcium needs.
However, people who eat well-designed plant-based diets have little difficulty meeting recommended intakes for these and most other nutrients. The single exception is vitamin B12—plants aren’t reliable sources. However, many vegan foods are fortified with vitamin B12, and supplements are inexpensive and widely available. In addition, everyone older than 50 (including nonvegetarians) is advised to use fortified foods and supplements for B12—just as vegans do. (For more on vitamin B12, see pages 214 to 222.) Both vegan and omnivorous diets have the potential to adequately nourish a population, if appropriately planned, and to be risky, if poorly planned.
While “malnutrition” is generally associated with undernutrition (insufficient access to food, or hunger), actually, more people in the world experience another form of malnutrition: overnutrition (overconsumption of calories). By 2010, the number of people suffering from overnutrition exceeded the number of people suffering from undernutrition.2
Vegan diets rarely lead to under- or overnutrition. Research has consistently confirmed a greater prevalence of overnutrition, overweight, and obesity within general populations than within vegan populations.3–7 In the United States, an estimated 68 percent of the general population suffers from overnutrition, leading to overweight or obesity.8 This, in turn, increases the risk of type 2 diabetes, coronary artery disease, stroke, hypertension, nonalcoholic fatty liver disease, gallbladder disease, gout, osteoarthritis, sleep apnea, some cancers, and complications of pregnancy.9
A third type of malnutrition, micronutrient deficiency, overlaps with both under- and overnutrition. Micronutrient deficiencies are common across all dietary groups. They can result from insufficient access to food, poor variety in the diet, and/or excess consumption of fat and sugar, which crowds out more-nutritious foods. In vegan populations, micronutrient deficiencies—especially vitamin B12 deficiency—are more prevalent in people who consume overly restrictive diets.
Research to date that assesses the overall dietary intakes and nutritional status of vegans provides reassurance that well-planned vegan diets supply adequate nutrition. Generally, vegan diets contain greater amounts of iron, folate, thiamin, magnesium, potassium, manganese, fiber, beta-carotene, and vitamins B6, C, and E than omnivorous diets. However, they may contain lower amounts of zinc, iodine, calcium, selenium, riboflavin, and vitamins B12 and D, so it’s important for vegans to include reliable sources of these nutrients. The bottom line is that animal products aren’t necessary for healthful and nutritionally adequate diets.
Table 2.1 provides a summary of research that addresses the overall nutritional adequacy of vegan diets for adults and adolescents. (Research on single nutrients is discussed in upcoming chapters, as is research pertaining to infants and children.) The studies included in table 2.1 focus specifically on vegans rather than on the broader vegetarian community.
TABLE 2.1. Summary of vegan research (adults): body mass index (BMI), overall nutrient intakes, and status
*Vegans were listed as “strict vegetarians” in this study and defined as individuals who reported consuming each of the following not at all or less than one time per month: meat (red meat, poultry), fish, eggs, milk, and dairy products.
When interpreting these results, it’s important to recognize potential limitations. First, the strength of the evidence is reduced when few subjects are followed. Second, while the most revealing evidence would come from lifelong vegans, currently, few individuals fit this bill. Third, vegans, like vegetarians or omnivores, aren’t a homogeneous group. Researchers don’t always tease out which vegans eat heathfully and which do not; nor do they distinguish vegans who adopted their diets in an effort to overcome an existing medical condition.
Finally, some methods used to obtain dietary information are far from foolproof. Often, diet recalls or food-frequency questionnaires are used; responses may provide only very rough estimates of food intake. In addition, participants may be followed for too short a time to obtain sufficient information about changes in their nutritional status.
Evidence regarding disease rates in vegan populations continues to flow into scientific journals at ever-increasing rates. Much of this data is sourced from studies of two large populations, both of which compare vegans to similar health-conscious vegetarians, semivegetarians, fish eaters, and meat eaters. The first population comprises members of the Seventh-day Adventist (SDA) church. The Adventist Health Study-1 (AHS-1) followed 34,198 California Adventists between 1974 and 1988, resulting in dozens of research papers. The Adventist Health Study-2 (AHS-2), which began in 2002, includes Adventists from across the United States and Canada, and is ongoing. Of the 96,000 participants in AHS-2, 28 percent are vegetarian and 8 percent are vegan. While some preliminary results from AHS-2 have been released, findings are expected to be published for several years.
The second large population participates in the European Prospective Investigation into Cancer and Nutrition (EPIC). With approximately 520,000 participants from ten European countries, EPIC is the largest cohort study of diet and health to date. The United Kingdom’s EPIC-Oxford is one of twenty-three EPIC centers; it’s unique among the centers because it purposefully recruited as many vegetarians and vegans as possible. Of the 65,500 people enrolled in EPIC-Oxford, approximately 29 percent were vegetarian and 4 percent were vegan when they enrolled. Research on this cohort is ongoing, although several reports have already been published. Other smaller but significant cohorts from the United Kingdom (Health Food Shoppers and Oxford Vegetarian Study) and Germany (Heidelberg Study) have also been followed.
Chronic diseases, such as cardiovascular diseases (CVD), diabetes, cancers, and lung diseases, are responsible for more deaths worldwide than all other causes combined. In 2008, 63 percent of global deaths were due to these conditions.18 According to the World Health Organization (WHO), by 2020, chronic diseases will be responsible for almost three-quarters of deaths globally.19
According to the 2010 WHO Global Status Report on Noncommunicable Diseases, the four primary causes of the epidemic are an unhealthy diet, physical inactivity, tobacco use, and alcohol consumption.18 Simply put, the majority of premature deaths globally are self-inflicted. This is no revelation—the alarm was sounded decades ago.
In 1990, a WHO technical report, Diet, Nutrition, and the Prevention of Chronic Diseases, singled out two food categories as being largely responsible for the epidemic of diet-induced chronic disease: energy-dense foods of animal origin and foods processed or prepared with added fat, sugar, and salt.20 The foods most strongly linked to disease-risk reduction were whole plant foods, namely vegetables, fruits, cereals, and legumes. Since then, evidence supporting the benefits of plant-based diets has continued to mount.
In response, health organizations have revised diet and nutrition recommendations to reflect the current state of knowledge. For example, the 2010 Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans suggests four major action points for Americans.21 These include eating less; exercising more; reducing intakes of refined grains and foods with added sugars, solid fats, and sodium; and shifting to a more plant-based diet that emphasizes vegetables, beans, peas, fruits, whole grains, nuts, and seeds.
Recent studies suggest that vegans come closer to meeting international and national nutrition recommendations for total fat, saturated fat, cholesterol, trans-fatty acids, and fiber than other dietary groups.1,22 In addition to being low in saturated fat, high in fiber, and cholesterol-free, vegan diets provide abundant antioxidants and protective phytochemicals. Not surprisingly, AHS-2 reported a 15 percent reduced mortality rate in vegans and a 9 percent reduced mortality rate in lacto-ovo vegetarians compared to similar health-conscious nonvegetarians.23 It’s little wonder that vegan diets are rising stars in the quest to combat chronic disease.
In 2005, CVD accounted for 30 percent of all deaths and still is a leading cause of death worldwide.24 However, years of scientific research have established that plant-based diets have a beneficial effect on CVD risk.25 The data also confirm significant risk reduction in vegetarian populations.26–29
In 2013, both EPIC-Oxford and AHS-2 released data on vegetarian and vegan rates of CVD. EPIC-Oxford found that vegetarians (including both lacto-ovo vegetarians and vegans) had a 32 percent lower risk of ischemic heart disease compared to meat and fish eaters when adjusted for confounding variables, except body mass index (BMI), and a 28 percent lower risk when BMI was factored in.30 AHS-2 reported a 19 percent risk reduction for ischemic heart disease in vegetarians (including lacto-ovo vegetarians and vegans), and a 13 percent risk reduction for CVD compared to nonvegetarians. The most significant findings were for vegan men, who experienced a 55 percent risk reduction in ischemic heart disease and a 42 percent risk reduction in CVD compared to nonvegetarians. (Vegan women experienced no risk reduction compared to non-vegetarian women.) Because men are at higher risk and often consume larger portions of meat, it’s possible they enjoy a greater benefit from consuming a plant-based diet.23
In a 1999 meta-analysis of five prospective studies of health-conscious populations (vegetarians, vegans, fish eaters, and meat eaters), death rates for vegans were reported for four of the five studies (one study didn’t separate vegans from vegetarian participants). Ischemic heart disease mortality in vegans was 26 percent lower than for participants who regularly ate meat (compared to 34 percent lower mortality for both vegetarians and fish eaters). However, vegans had a 30 percent lower risk of cerebrovascular disease (compared to 13 percent lower for vegetarians and 4 percent higher for fish eaters), although due to the small number of events, this finding was not statistically significant.25
While the 1999 meta-analysis suggested that vegan diets provide a stronger protective effect against stroke compared to all other dietary patterns, both vegetarians and fish eaters enjoyed greater protection against ischemic heart disease. It’s interesting to note that the 2013 EPIC-Oxford study found no lower risk of ischemic heart disease in fish eaters compared to meat eaters. Although the reason for this finding isn’t clear, it’s possible that fried fish, a favorite in the United Kingdom, could have predominated in the diets of the fish eaters.
Although there’s no question that meat eaters have a more ominous cluster of cardiovascular risk factors than vegans, one might have expected vegans to fare even better than they did.31 The results might have been more impressive if the vegans in these studies had been lifelong vegans, or at least longtime vegans (ten years or more). Of course, vegan diets may favorably affect some CVD risk factors, while negatively affecting others. As a result, it’s important for vegans to be aware of any potential dietary pitfalls that may increase CVD risk and take steps to avoid them.
There are many known risk factors for CVD, some of which are modifiable by diet and lifestyle changes and others that aren’t (e.g., age, gender, and family history). Among the risk factors that can be controlled, some are considered “major” modifiable risk factors, while others are classified as “emerging” risk factors. Although all the major modifiable risk factors are favorably impacted by vegan diets, the effects on emerging risk factors are more variable.
Elevated Blood Cholesterol Levels The dietary factors linked to elevated blood cholesterol levels are saturated fat, trans-fatty acids, and to a lesser extent, dietary cholesterol.32 It’s estimated that for every 1 percent decrease in cholesterol levels, there’s a 2 to 4 percent decrease in heart disease risk.22 The most effective cholesterol-lowering food components are soluble fiber, plant protein, plant sterols and stanols, polyunsaturated fats, and phytochemicals—all of which are found exclusively or predominantly in plant foods. Vegans consume no cholesterol, have the lowest saturated-fat intake of all dietary groups, and have lower trans-fatty acid intakes.22,33,34 While there’s good evidence that replacing saturated fat with polyunsaturated fat significantly reduces CVD risk, replacing saturated fat with refined carbohydrates (e.g., white-flour products, white rice, and sugar-sweetened beverages and treats) elevates CVD risk.35 Although intakes of refined carbohydrates vary in vegan diets, vegans generally consume a higher proportion of carbohydrates from unrefined foods than do nonvegetarians.
Not surprisingly, in twenty-four studies of vegan, lacto-ovo vegetarian, and nonvegetarian populations conducted from 1978 to 2007, the total blood cholesterol levels of vegans were shown to be lower than those of any other dietary group, averaging approximately 150 mg/dl (3.9 mmol/L).22 This compares to 187 mg/dl (4.84 mmol/L) for the lacto-ovo vegetarians and 193 mg/dl (5 mmol/L) for the nonvegetarians in these studies (see table 2.2 on page 38).
The vegan average of 150 mg/dl (3.9 mmol/L) is a bit of a magic number in the medical world. According to Dr. William Castelli, former director of the Framingham Heart Study (the longest-running epidemiological study ever conducted) and current medical director of the Framingham Cardiovascular Center, “In the first fifty years of Framingham, only five subjects with a cholesterol level less than 150 mg/dL developed coronary artery disease.”36
Although there was a significant difference in the low-density lipoprotein cholesterol (LDL) levels of vegans compared to those of other dietary groups, the differences in high-density lipoprotein cholesterol (HDL) were small. The LDL levels of vegans averaged approximately 85 mg/dl (2.2 mmol/L), compared to 105 mg/dl (2.7 mmol/L) for lacto-ovo vegetarians and 119 mg/dl (3.1 mmol/L) for nonvegetarians (see table 2.2). The HDL levels of vegans averaged approximately 49 mg/dl (1.27 mmol/L), compared to 52 mg/dl (1.35 mmol/L) for lacto-ovo vegetarians and 54 mg/dl (1.4 mmol/L) for nonvegetarians.22 It’s important to note that most study participants (regardless of their dietary group) were from health-conscious populations, making these differences less pronounced than they would have been had vegans been compared to the population at large.
In addition to having lower cholesterol levels, vegans also appear to be at an advantage when it comes to cholesterol metabolism. A 2011 study from Brazil found that vegans experienced increased removal of artery-clogging remnants (specifically cholesterol) and reduced cholesterol ester transfer, both of which favor atherosclerosis prevention.37
Dietary cholesterol has been shown to increase the susceptibility of LDL to oxidation by nearly 40 percent.38,39 When cholesterol becomes oxidized, it has negative effects on arteries, promoting plaque formation and causing hardening of the arteries (reducing their elasticity). The susceptibility of LDL to oxidation can be reduced by the presence of antioxidants, such as vitamin E, carotenoids, vitamin C, flavonoids, and polyphenolic compounds.
Antioxidants come primarily from whole plant foods and are generally more concentrated in typical vegan diets, compared to typical omnivorous diets.22,28,40 Limited evidence suggests that adopting a vegan diet or other plant-based diet improves antioxidant status and decreases the oxidation of lipids (fats).41–44 In addition, some evidence suggests that high intakes of heme iron (iron from meat, as opposed to nonheme iron from plants) may act as a prooxidant, increasing LDL oxidation and atherosclerosis.45,46 Vegans don’t consume heme iron, possibly providing further protection against CVD.
Table 2.2 shows CVD-related lab values and dietary intakes, which compare the averages from studies of vegan, lacto-ovo vegetarian, and nonvegetarian populations conducted between 1979 and 2008. The figures were not weighted according to the number of participants in each study.
Elevated Triglyceride Levels One common criticism of plant-based diets has been that they can increase blood triglyceride levels. However, this tends to occur only when refined carbohydrates (sugars and flour products) are overconsumed, because the body converts them into triglycerides for storage purposes. Other dietary factors linked to elevated triglycerides are more strongly associated with omnivorous diets; these include overconsumption of calories and excessive intakes of total fat, saturated fat, trans-fatty acids, cholesterol, and alcohol.
TABLE 2.2. Average CVD-related lab measures and dietary intakes
Source: 22
Many lifestyle factors can help to keep triglycerides in check, including physical activity; abstaining from alcohol; minimizing intake of sugar and products made with white flour; and eating a low-fat, high-fiber, omega-3-rich plant-based diet. Research suggests that vegans have the lowest triglyceride levels of all dietary groups. In sixteen studies conducted between 1979 and 2007, vegan triglyceride levels averaged 83.5 mg/dl (0.94 mmol/L), compared to 107.8 mg/dl (1.2 mmol/L) for lacto-ovo vegetarians and 95.5 mg/dl (1.1 mmol/L) for meat eaters.22
Hypertension (High Blood Pressure) Blood pressure in vegans is generally within a healthy range, and few vegans have high blood pressure.47–53 Studies have consistently reported differences in blood pressure in vegetarians compared to non-vegetarians, ranging from 5 to 10 mmHg systolic and 2 to 8 mmHg diastolic.54–56
A 2009 AHS-2 report found that, compared to nonvegetarians, the incidence of hypertension was 75 percent lower for vegans. Although hypertension was self-reported in this study, it had been diagnosed by a physician and treated within the previous twelve months.52 In 2012, further findings of AHS-2 were released.53 While the risk reduction wasn’t quite as strong as in the 2009 report, the later study reported that vegans had a 63 percent reduction in the risk of developing hypertension compared to nonvegetarians.
In EPIC-Oxford, self-reported, age-adjusted, physician-diagnosed hypertension in study participants ranged from 5.8 percent in male vegans to 15 percent in male meat eaters and 7.7 percent in female vegans to 12.1 percent in female meat eaters.51 While an individual’s BMI is strongly associated with his or her blood pressure levels, it was estimated that only about half the variation in hypertension could be attributed to the study subjects’ BMI. The remainder was attributed to dietary factors, such as intakes of fat, saturated fat, sodium, alcohol, and fiber, and nondietary factors, such as physical activity.
Increasing the intake of long-chain omega-3 fatty acids (mainly through fish consumption) has been shown to be effective in reducing hypertension.58 However, EPIC-Oxford didn’t report an advantage for fish eaters compared to vegans, suggesting that other factors have a greater impact.51
In addition, although omega-3 fatty acids from fish may be protective, fish is also the most concentrated food source of mercury. It’s possible that if contaminated fish are consumed, the protection against hypertension afforded by long-chain omega-3 fatty acids could be offset by mercury. The potential consequences of mercury toxicity include a number of cardiovascular diseases, as well as renal dysfunction, insufficiency, and proteinuria.59
Overweight and Obesity Vegans have a decided advantage in maintaining healthy body weight and composition when compared to similar health-conscious non-vegetarians. Since 1990, more than twenty studies have consistently reported that vegans are leaner than people in other dietary groups and have both a lower BMI and a lower percentage of body fat.22
The two largest studies are AHS-2 and EPIC-Oxford. In the British EPIC-Oxford studies, although average BMIs for all dietary groups were within the healthy BMI range, meat eaters had the highest BMIs, while vegans had the lowest.5 In four American AHS-2 reports, only the average BMI of vegans falls within this optimal BMI range. The mean BMI for vegans was between 23.6 and 24.1 in these studies, compared to 28.2 to 28.8 for meat eaters—a 4.6 to 4.7 point difference.3,4,30,60 EPIC-Oxford found a 1.92-point difference between male vegans and meat eaters and a 1.54-point difference between female vegans and meat eaters.5 However, age-adjusted obesity rates (BMI > 30) were 2.6 times higher in male meat eaters compared to male vegans and 3.2 times higher in female meat eaters compared to female vegans.
In the EPIC-Oxford study, nondietary lifestyle factors, such as smoking and exercise, explained only about 5 percent of the difference in BMI between the dietary groups; their effects may have been diluted because of the health-conscious nature of the cohort. In contrast, energy and macronutrient intakes (i.e., calories, fat, protein, and carbohydrate) explained about half the difference.
The dietary factors judged to be most strongly linked to a higher BMI were low fiber and high protein intake (as a percentage of calories). Although high protein intake itself isn’t commonly associated with weight gain, study authors suggested that hormonal changes induced by diets rich in protein may alter metabolic systems to favor weight gain.5 Meanwhile, increasing fiber intake appears to improve satiety, reduce fat absorption, and promote better insulin control, thereby resulting in lower BMIs.
Relative fiber and protein intakes were significantly associated with BMIs in all dietary groups except vegans. The absence of an association within the vegan group was thought to be related to small variations in intakes within this group. The authors suggested that in the case of protein, it’s possible that only high intake of animal protein is associated with increased BMI, so for vegans, varying the percentage of plant protein in their diets wouldn’t affect BMI.5
Inflammation Chronic inflammation can make arterial plaque vulnerable to rupture and thrombosis, heightening the risk of a coronary event. Generally, lifestyle factors, such as smoking, inactivity, being overweight, and poor food choices, can contribute to such inflammation and elevate blood levels of high-sensitivity C-reactive protein (hs-CRP), a predictor of cardiac risk. An hs-CRP of less than 1 mg/L is considered low risk for CVD, 1 to 2.9 mg/L suggests intermediate risk, and above 3 mg/L is associated with high risk.61 Although levels of hs-CRP in vegans aren’t well-known, four of five studies assessing hs-CRP levels in vegetarians showed significantly lower inflammation frequency in vegetarians compared to omnivores.62–66
The only study assessing vegan hs-CRP levels found markedly lower levels in vegans (0.57 mg/L) compared to endurance athletes (0.75 mg/L) and those who followed standard Western diets (2.61 mg/L).67 Although this study was small (63 participants), the differences were striking. In addition, the vegan diet in this study was largely raw.
Poor Antioxidant Status Although the relationship between antioxidant status and CVD risk remains uncertain, vegans and vegetarians, who generally consume larger amounts of antioxidants than nonvegetarians, may be at an advantage. Several studies have reported better antioxidant status in vegetarians, vegans, and raw vegans than in nonvegetarians, although in some studies, benefits were limited to some, but not all, measures of antioxidant status.43,68–75 It’s important to note that although antioxidants from food appear to be protective, research on antioxidant supplements has been less encouraging.
Increased Carotid Intima-Media Thickness (Carotid IMT) There’s evidence to suggest that dietary changes can affect carotid IMT (a measure of the thickness of artery walls and of arterial stiffness and damage to the blood vessels). Diets high in meat and low in fiber can increase arterial stiffness, and vegan or near-vegan diets can decrease it.67,76,77 In addition, a recent study from Hong Kong reported improved arterial function (including carotid IMT) in vegetarians who have been provided vitamin B12 supplementation to treat low B12 levels.78
High Trimethylamine N-Oxide (TMAO) TMAO is produced when intestinal bacteria ingest carnitine and produce trimethylamine (TMA), which is taken to the liver and converted to TMAO. Although research on TMAO is very preliminary, this is an emerging risk factor worth noting. Researchers suggest that high TMAO levels may accelerate atherosclerosis and hardening of the arteries, increasing the risk of major cardiac events.
Diets determine the amount of TMAO a body makes. The carnitine used for its formation is found in animal products—mainly red meat. Omnivores who regularly consume red meat are ideal hosts for TMA-producing bacteria; regular meat consumption encourages their growth and increases TMAO production. Vegans have none of these bacteria. Even when vegans are fed carnitine supplements, they don’t produce TMA because they lack the bacteria to do so. Avoiding meat gradually reduces the gut bacteria that turn carnitine into TMA, and ultimately TMAO, providing a further incentive to adopt a vegetarian or vegan diet.79
Elevated Homocysteine Levels Although the amino acid homocysteine occurs naturally in humans, elevated homocysteine damages blood vessel walls—triggering blood clots, oxidative stress, and inflammation—and has been shown to be highly predictive of CVD and coronary events.80,81 Three B vitamins—folic acid, vitamin B6, and vitamin B12—serve as the standard treatment for elevated homocysteine, but research results have been inconsistent, and the value of B-vitamin therapy for reducing CVD risk has come into question.82–96
While the utility of B-vitamin therapy for reducing homocysteine and CVD risk continues to incite lively debate, we do know that poor folate, B6, and B12 status is associated with elevated homocysteine. While vegans generally have excellent folate and vitamin B6 status, their vitamin B12 status tends to be low, especially if they don’t use supplements. Although it isn’t known precisely how low serum B12 must be to compromise homocysteine metabolism, one study suggested that when serum B12 falls below 300 pg/ml (222 pmol/L), homocysteine levels rise.97 Experts recommend that patients with serum B12 below 400 pg/ml should be further tested for vitamin B12 deficiency, including tests for homocysteine and serum methylmalonic acid (MMA).98 Levels above 400 pg/ml (300 pmol/L) are considered safe; thus, this seems a prudent target for vegans.
Finally, researchers have reported a significant positive correlation between poor omega-3 fatty-acid status and elevated homocysteine, particularly in subjects who had high blood levels of adrenic acid, a long-chain omega-6 fatty acid, and low blood levels of docosahexaenoic acid (DHA), a long-chain omega-3 fatty acid.31,99 Treatment with DHA has successfully lowered homocysteine levels in DHA-depleted subjects.31
Abnormal Blood Coagulation Several scientific studies have examined markers for the tendency to form blood clots in vegetarians, including vegans and near-vegans. Few of these studies have included enough vegans to make those results statistically significant, but three of four studies reported lower levels of the coagulation protein, factor VII, in vegetarians compared with nonvegetarians,100–102 two of four studies reported lower levels of fibrinogen in vegetarians compared to nonvegetarians,101,103 and two studies found no significant difference.104,105 Better fibrinolysis in vegetarians and vegans compared to nonvegetarians was reported in one study,103 while another found better blood fluidity in vegetarians.104
Surprisingly, two relatively recent studies using sensitive test methods reported higher platelet aggregation in vegetarians than in nonvegetarians.101,102 The negative findings for platelet aggregation are contrary to expectations because many dietary factors associated with increased platelet aggregation, such as saturated fat and cholesterol, are reduced in vegetarian and vegan diets. In addition, intake of some dietary factors known to diminish platelet aggregation (such as phytochemicals in vegetables, fruits, and herbs) tend to be increased in vegetarian and vegan diets.
Experts suggest that most plausible explanation for this discrepancy is that some vegetarians have poor omega-3 status and high intakes of omega-6 fatty acids. (For more on fatty acids, see pages 117 to 134.) A recent review study suggests that vegetarians—especially vegans—would benefit from eating more omega-3 fatty acids and improving the balance between omega-3 and omega-6 fatty acid intakes.31
Poor Vitamin D Status Several large epidemiological studies have confirmed that suboptimal vitamin D status causes significant increases in CVD risk.106–108 Although this is a concern for all dietary groups, it’s well-known that vegan populations tend to have reduced levels of vitamin D, which could have adverse consequences for their cardiovascular health.
Vegan and near-vegan diets have been used in a variety of trials to improve specific CVD markers, such as high blood lipid levels and high blood pressure, and to treat severe coronary artery disease (CAD).
A well-planned vegan diet offers, quite arguably, the most powerful protection against cardiovascular disease (CVD) that can be provided by any diet. However, the degree of protection can vary considerably, depending on the overall quality of the vegan diet. A poorly planned vegan diet may not provide any advantage over a nonvegetarian diet and could end up increasing CVD risk. To provide maximum protection against lipid abnormalities and cardiovascular disease, vegan diets should include unprocessed, whole plant foods as dietary staples and reliable sources of vitamin B12, vitamin D, and omega-3 fatty acids.
A review study reporting on data collected between 1975 and 2007 found that lacto-ovo vegetarian dietary interventions resulted in total and LDL cholesterol reductions of 10 to 15 percent. Vegan dietary interventions were associated with decreases of 15 to 25 percent, while vegan diets rich in specific protective components (e.g., plant sterols, viscous fiber, soy protein, and nuts) resulted in reductions of 20 to 35 percent.109 Generally, vegan or near-vegan diets also slightly reduce HDL cholesterol, but observational studies suggest lower HDL levels don’t increase cardiovascular risk when associated with a low-fat plant-based diet. While some trials reported increases in triglyceride levels, the reverse was true for trials that featured diets rich in whole high-fiber plant foods.109
Two researchers have demonstrated that very low-fat vegan or near-vegan diets can effectively reverse established CAD. In 1983, Dr. Dean Ornish used a combination of diet (10 percent fat, near-vegan), exercise, and stress management to treat 23 patients, comparing them with 23 controls who were asked to make no lifestyle changes. This pioneering work provided initial evidence that comprehensive diet and lifestyle changes could actually reverse CAD.110
In 1990, Ornish published his landmark study, The Lifestyle Heart Trial.111 In this study, 28 participants were randomized to a lifestyle intervention group and 20 to a control group. The participants making lifestyle changes similar to those in his 1983 study experienced dramatic improvements in cardiac health. Eighty-two percent of the experimental group experienced regression of their coronary blockages, while 53 percent of the control group experienced progression. Angina frequency fell 91 percent in the experimental group and jumped 165 percent in the control group. LDL cholesterol dropped approximately 37 percent in the experimental group, compared to 6 percent in the control group. In a five-year follow-up, more improvements were reported, including further regression in arterial blockages. By then, experimental participants had 2.5 times fewer cardiac events than control-group participants.112,113
The second researcher, Dr. Caldwell Esselstyn, used a very low-fat, near-vegan diet plus cholesterol-lowering medications (if necessary) to treat 24 patients with severe CAD. At the five-year follow-up, none of the 18 patients who adhered to the program had experienced a cardiac event. Of 11 patients who had undergone angiography, none had progression of their blockages—and eight had significant regression. No one on the program experienced disease progression, a cardiac event, or cardiac interventions; one person temporarily left the program, but returned when symptoms reappeared.113
In 2014, Dr. Esselstyn released a study that followed 198 patients with established CVD, 177 who were compliant with a very low-fat vegan diet and 21 who were not. Of the compliant patients, one individual had a cardiac event (a stroke)—a recurrence event rate of 0.6 percent. Thirteen of the 21 noncompliant patients experienced a cardiac event—a recurrence rate of 62 percent.114
No current studies exist on whether higher-fat vegan or near-vegan diets cause positive changes in artery lesions and blockages. However, case reports dating back to the mid-1970s suggest significant improvements in coronary health with the use of higher-fat vegan diets. British researchers Dr. Frey Ellis and Thomas Sanders published reports of patients suffering from severe angina who completely eliminated symptoms after a few months on a strict vegan (but not low-fat) diet.115,116 Canadian researcher David Jenkins successfully and dramatically lowered lipids in patients using his trademark “portfolio diet,” a vegan program that maximizes plant sterols and viscous fiber and includes soy foods and nuts.117–121 Investigators have also reported remarkable improvements in cardiovascular markers in participants who consume higher-fat raw diets.67,122–125
There’s no doubt that very low-fat vegan diets are particularly effective in treating severe CAD. However, a question that remains is how the addition of nuts, seeds, or avocados would affect the results. It’s possible that bioactive compounds and nutrients in these foods and their beneficial effect on nutrient absorption could reduce inflammation, drive down triglyceride levels, increase HDL levels, and further improve outcomes. Of course, it’s also possible that dietary fat intake from any source needs to be minimized to reverse coronary blockages. Ongoing research will eventually answer these questions. For now, whole-foods vegan diets are powerful allies in the battle against the world’s leading killer.
Cancer, the most dreaded of all chronic diseases, is currently the second largest cause of death globally, and the rates are rising.126,127 Although perhaps its onset is less predictable than heart disease or type 2 diabetes, cancer is no indiscriminate killer. Surprisingly, a mere 5 to 10 percent of cancers are determined by individuals’ genes; the remaining 90 to 95 percent of cancers are products of their environment.
Although it’s tempting to assume that populations with low cancer rates will always be protected, migration often wipes out any advantage within a generation or two. One study that followed Japanese women who migrated to Hawaii reported a nearly threefold increase in breast cancer rates in the first generation to reside in Hawaii and a fivefold increase in the second generation. Rates of colon cancer in these migrants also jumped almost fourfold within the first generation (it didn’t increase further in the second).128
TABLE 2.3. Estimated contribution of diet to cancer deaths
TYPE OF CANCER |
PERCENT OF DEATHS LINKED TO DIET |
Prostate |
75 |
Colorectal |
70 |
Breast, endometrial, gallbladder, and pancreatic |
50 |
Gastric (stomach) |
35 |
Lung, larynx, pharynx, esophagus, mouth, and bladder |
20 |
Other |
10 |
Source:129
Evidence suggests that diet is the linchpin, accounting for an estimated 30 to 35 percent of all cancers. Beyond food choices, an estimated 25 to 30 percent of cancers (87 percent of lung cancers) are primarily due to smoking, 15 to 20 percent are linked to infections, 10 to 20 percent are triggered by obesity, and 4 to 6 percent are tied to alcohol ingestion. The balance is thought to be caused by a variety of factors, such as radiation, stress, inadequate physical activity, and environmental contaminants.129
The degree to which diet serves as a causative factor varies according to the type of cancer. As shown in table 2.3, the impact of diet varies with the cancer type or site and is particularly high in the hormone-related and intestinal (colorectal) cancers prevalent in those following Western diets.
In a laudable effort to reduce the global burden of cancer, the World Cancer Research Fund and the American Institute of Cancer Research (WCRF/AICR) convened two expert panels to determine the strength of the existing evidence linking diet and lifestyle factors to cancer. Foods, food components, supplements, dietary patterns, physical activity, body composition, and body fatness were all factored in and scrutinized. The reports present judgments regarding these factors and their relative impact on cancer risk for seventeen potential cancer sites. Released in 1997 and 2007, these reports are considered the most authoritative and influential in this field to date.130,131 WCRF/AICR’s Continuous Update Project (CUP) also monitors scientific findings on an ongoing basis and maintains a central database of evidence. This allows the panel to review and revise recommendations as new evidence presents itself.
Table 2.4 (page 46) provides an abbreviated version of the 2007 findings as they relate to six of the cancers most directly impacted by food choices. Evidence listed as “convincing” or “probable” was deemed strong enough to include in public health goals (meant for health professionals) and personal recommendations (meant for communities, families, and individuals). Evidence listed as “limited” or “suggestive” was considered insufficient as a basis for public health goals and personal recommendations, although it was strong enough to show a generally consistent trend toward either reducing or increasing cancer risk.
TABLE 2.4. Dietary and other factors that affect cancer risk
*In the 2007 report, the evidence was probable; however, in 2011, the panel strengthened the judgment to convincing.
The WCRF/AICR Panel established a set of public health goals and personal recommendations based on probable and convincing findings that would be most likely to provide the greatest protection against cancer. These recommendations are provided below, along with brief comments regarding rationale, mechanisms, and/or current state of knowledge.131
Body Fatness Be as lean as possible within the normal range of body weight. Ideally, body weight throughout childhood and adolescence should be at the lower end of the normal BMI range. Maintain body weight within the normal range from age 21. Avoid weight gain and increases in waist circumference throughout adulthood.
Although carrying some body fat appears to protect against premenopausal breast cancer, excessive increases in body fatness are associated with cancers of the esophagus, colorectum, pancreas, breast (postmenopause), kidney, gallbladder, and liver. Increased body fatness causes changes in hormones and hormone-like chemicals, such as insulin-like growth factor 1 (IGF-1), insulin, leptin, and sex steroids, and leads to increases in insulin resistance—all of which can trigger inflammatory sequences associated with cancer risk.
Physical Activity Be physically active as a part of everyday life. Be moderately physically active, aiming for an activity level equivalent to brisk walking for at least 30 minutes every day. As fitness improves, aim for 60 minutes or more of moderate activity or for 30 minutes or more of vigorous physical activity every day. Limit sedentary habits, such as watching television.
Some evidence links inactivity to cancers of the lung and pancreas. Consistent data suggest that physical activity protects against cancers of the colon, breast (postmenopause), and endometrium, and it likely protects against cancers associated with excess body fatness. The mechanism by which this occurs varies with each type of cancer. For example, physical activity reduces intestinal transit time, shrinking the amount of time dietary carcinogens reside in the intestinal tract, possibly reducing the chances of developing colon cancer. One study reported a 50 percent reduction in colon cancer in those with the highest levels of physical activity.132 Exercise also favorably affects hormone metabolism and reduces body fat.
Foods and Drinks that Promote Weight Gain Limit consumption of energy-dense foods. Avoid sugary drinks. Consume processed energy-dense foods sparingly. (This advice doesn’t refer to unprocessed foods, such as nuts and seeds, which haven’t been shown to contribute to weight gain.) Avoid drinks with added sugar; the panel also recommends limiting fruit juices. Eat fast foods sparingly, if at all.
Consuming energy-dense foods and sugary drinks is associated with overconsumption and weight gain, which increase cancer risk. Generally, processed foods with added fat and sugar have the highest energy density. While sugary beverages aren’t as energy dense (due to their water content), they fail to induce satiety the way solid foods do, and thus, are often overconsumed.
Plant Foods Eat mostly foods of plant origin. Eat at least five servings (at least 14 ounces/400 g) of a variety of nonstarchy vegetables and fruits every day. Eat relatively unprocessed cereals (grains) and/or legumes (pulses) with every meal. Limit refined starchy foods. People who consume starchy roots or tubers as staples should also ensure intake of five servings of nonstarchy vegetables, fruits, and legumes (pulses).
Plant foods are protective throughout the body. Of the seventeen cancer sites included in this report, risk reduction with plant food intake was reported for fourteen sites. Plant-based foods tend to be relatively low in calories but high in nutrients (such as vitamins and minerals) per calorie, helping to reduce the risk of overweight and obesity and enhancing nutritional status. In addition, these foods are high in numerous protective compounds, including dietary fiber, antioxidants, and phytochemicals, which can help to protect the body from cell damage that can lead to cancer.
Today, the WCRF/AICR’s recommendation for a plant-based diet—including fiber-containing foods, such as whole grains, fruits, vegetables, and beans—is stronger than it was in 2007. A recent meta-analysis reported that for people with low fiber intakes, every 10 grams of added dietary fiber was associated with a 10 percent reduced risk of colorectal cancer.133 In 2011, CUP stated that research published since 2007 has further strengthened the judgment from “probable” to “convincing” that fiber-containing foods protect against bowel cancer.134
Animal Foods Limit intake of red meat and avoid processed meat. People who eat red meat (beef, pork, lamb, and goat) should restrict their consumption to fewer than 18 ounces (500 g) per week. Very little of this intake, if any, should be processed (meat preserved by smoking, curing, or salting, such as bacon, salami, pastrami, corned beef, and ham).
The evidence linking red and processed meat to colorectal cancer was convincing at the time of the 2007 report. There was also limited evidence suggesting that red meat causes cancers of the esophagus, lung, pancreas, and endometrium; that processed meat causes cancers of the esophagus, lung, stomach, and prostate; and that grilled, barbecued, or smoked meat causes stomach cancer.
In 2011, CUP issued a press release noting that ten new studies conducted since the 2007 report had further strengthened the evidence linking both red and processed meat to bowel cancer. According to this review, the risk of bowel cancer increases 17 percent when a person eats 3.5 ounces (100 g) of red meat per day and 36 percent when one eats 3.5 ounces (100 g) of processed meat per day.134
Although scientists aren’t certain why red meat increases cancer risk, it’s known that cancer-causing compounds can be generated by heme iron, which is present in all these meats; by nitrates, nitrites, and N-nitroso compounds present in processed meats; and by high-temperature cooking, which can produce known carcinogens, such as heterocyclic amines.
Alcoholic Drinks Limit alcoholic drinks. If alcoholic drinks are consumed, limit consumption to no more than two drinks a day for men and one drink a day for women. There is convincing evidence that alcohol increases the risk of mouth, pharynx, larynx, esophageal, bowel (men), and breast cancers. Alcohol also probably increases the risk of liver cancer and bowel cancer in women. The evidence suggests that all types of alcoholic beverages are implicated and that there’s no safe level of intake. Based solely on cancer data, alcohol should be completely avoided.
When epidemiologist Walter Willet, chair of the department of nutrition, Harvard School of Public Health, was asked, “How much red meat is okay?” he replied, “Like almost everything, it’s frequency and amount that influence our risk. There’s no sharp cut-off. It’s like radiation. We can’t say that there’s any safe amount.”135
With its ability to act as a solvent, alcohol has the potential to ease the entrance of carcinogens into cells. Alcohol also produces reactive metabolites, such as acetaldehyde, and generates free radicals. Worse, alcohol and tobacco act synergistically to increase cancer risk. The body’s ability to repair genetic mutations caused by tobacco is blunted by alcohol.
Preservation, Processing, Preparation Limit consumption of salt. Avoid moldy cereals (grains) or legumes (pulses). Avoid salt-preserved, salted, or salty foods; preserve foods without using salt. Limit consumption of processed foods with added salt to ensure an intake of less than 6 grams (2.4 g) of sodium a day. Note that only 11 percent of salt eaten is added at the table or during cooking; most is in processed foods. (For more on sodium, see pages 201 to 203.) Don’t eat moldy cereals (grains) or legumes (pulses).
Some techniques of food preservation, processing, and preparation are associated with increased cancer risk. Examining consumption of processed meats, salted foods, and foods preserved by salting, smoking, and pickling provides the most compelling evidence for increased risk. Salt has been deemed a probable cause of stomach cancer, and the expert panel estimated that 14 percent of stomach cancers could be prevented if intake were limited to less than 6 grams (2.4 g) of sodium per day.
Dietary Supplements Aim to meet nutritional needs through diet alone. Dietary supplements aren’t recommended for cancer prevention. Although several excellent indications for supplement use exist, such as vitamin B12 for vegans and vitamin D for people at northern latitudes, studies generally haven’t found that supplements are effective for cancer risk reduction. Some evidence suggests that high-dose supplements could even increase cancer risk.
Supplements rarely contain the complete mix of protective compounds naturally found in foods. For example, vitamin A pills are no substitute for health-supportive carotenoids in orange, yellow, and red vegetables and fruits. For this reason, the panel recommended relying on a wide variety of vegetables, fruits, and other plant-based foods for cancer protection, rather than supplements.
Judging from the findings and recommendations of the WCRF/AICR Panel, one would expect that well-planned vegan diets would provide impressive protection against cancer, especially forms of cancer closely tied to dietary choices. Vegans are leaner; they eat more fiber, more nonstarchy vegetables, more fruits, and more legumes; and they consume greater amounts of folate and antioxidant vitamins from foods. Vegans don’t eat meat or animal fat; they avoid dairy products and eat less total fat.
So, how do vegans fare when it comes to cancer? Evidence suggests that cancer risk is affected by choices throughout life, even choices in childhood. Although some information exists about cancer rates in vegetarian populations, it will likely be many years before reliable data on lifelong vegans is available. On the other hand, almost all studies on cancer among vegetarian populations show reduced cancer rates compared to the general population. Some, but not all, studies also report reduced cancer rates in vegetarians, compared to the cancer rates in similar health-conscious nonvegetarians.
A handful of studies have reported cancer rates in various dietary groups, including vegans. Although much of this data combines results for vegans with results for other vegetarians, AHS-2 recently provided data that separated vegan participants from other types of vegetarians.
In 2012, AHS-2 released a report examining cancer incidence in more than 69,000 people, with almost 3,000 incident cases of cancer. Vegans had a 16 percent reduced risk of developing cancer compared to meat-eating Adventists, and a 34 percent lower risk for female-specific cancers. This compares to the study’s lacto-ovo vegetarians, who experienced an 8 percent reduced risk of developing cancer and a 24 percent lower risk for cancers of the gastrointestinal tract.136 A second AHS-2 study reported an 8 percent risk reduction in deaths due to cancer for vegans compared to nonvegetarians, and a 10 percent risk reduction for lacto-ovo vegetarians. Vegan men had a 19 percent risk reduction in deaths from cancer compared to nonvegetarians.23
In 2014, the EPIC-Oxford group released findings of cancer rates in 61,647 British men and women after an average follow-up of almost fifteen years and 4,998 incident cancer cases. Compared to health-conscious meat eaters, total cancer risk was 19 percent lower in vegans, 11 percent lower in vegetarians, and 12 percent lower in fish eaters.
Among vegetarians and vegans (grouped together), risk was reduced by 63 percent for stomach cancer, 77 percent for multiple myeloma, 36 percent for lymphatic/hematopoietic tissue cancer, and 38 percent for bladder cancer. Rates of prostate cancer, breast cancer, and colon cancer for vegetarians and vegans were looked at separately. Although the findings were not statistically significant, prostate cancer rates were 38 percent lower among vegans, 13 percent lower among vegetarians, and 24 percent lower among fish eaters relative to health-conscious meat eaters. Female breast cancer was 13 percent lower among vegans, 6 percent lower among vegetarians, and 7 percent higher among fish eaters than among meat eaters. One surprising finding was higher colon cancer rates among vegans, although there were only 19 incident cases and the results were not statistically significant.137
Numerous testimonies and anecdotes report excellent responses in cancer patients who consume largely or completely plant-based diets. While such evidence is interesting, it doesn’t prove cause and effect, nor does it hold up to scientific scrutiny.
Well-constructed research on the effects of vegan diets on cancer is rare; however, one such study deserves mention. In a 2005 US prostate cancer study, the effects of lifestyle intervention (vegan diet, exercise, stress management, group therapy) were measured in men with early-stage prostate cancer who had opted against conventional therapy.138 Participants were randomized to either a control group or the lifestyle-intervention group.
After one year, six of the men in the control group began conventional therapy based on the progression of their disease and/or increasing prostate-specific antigen (PSA) levels; no one in the lifestyle-intervention group had to do so. PSA increased 6 percent in the control group and decreased 4 percent in the lifestyle-intervention group. In addition, prostate cancer cell growth was inhibited nearly eight times more in the lifestyle-intervention group than in the control group. This study provided compelling evidence that lifestyle intervention (including a vegan diet) effectively reduces cancer progression in early-stage prostate cancer. Further research is needed to see if similar benefits could be produced in patients with other forms of cancer.
Several studies have examined metabolic markers of cancer in vegans or in subjects fed a vegan diet. While metabolic markers of cancer are less clear-cut than those of heart disease or diabetes, they do provide some worthwhile information. One study compared metabolic markers for cancer in three groups: vegans (who ate predominantly raw diets), endurance athletes, and people consuming a nonvegetarian Western diet.139 Insulin-like growth factor 1 (IGF-1), a known tumor promoter, was much lower in the vegan group than in the Western-diet group and also significantly lower than in the endurance runners (even when the percentage of body fat was controlled for).Test results for several other metabolic markers of cancer risk were all more favorable in the vegans and endurance athletes than in the Western-diet group, with the vegans enjoying the greatest advantage.
A second study examined the IGF-1 levels of 292 vegan, vegetarian, and meat-eating women. Higher IGF-1 levels have been associated with increased breast cancer risk. The mean serum IGF-1 concentration was 13 percent lower in vegans compared to meat eaters or vegetarians. In addition, levels of IGF-binding proteins were higher in vegan women. This suggests the amount of available IGF-1 would be reduced among vegans, again reducing cancer risk for the vegans.140
A small Finnish study compared several laboratory markers of cancer prevention in 40 women; 20 consumed a vegan diet (mostly raw foods) and 20 consumed a nonvegetarian diet.73 Compared to the nonvegetarians, the vegan participants had less damage to DNA and/or better protection against DNA damage.
A second Finnish study assessed changes in metabolic markers of cancer in participants who consumed a vegan diet (mostly raw foods) for one month, followed by a conventional nonvegetarian diet for one month. The test participants were compared with controls who consumed a conventional nonvegetarian diet for the duration of the study.141 The researchers measured the activity of four different fecal enzymes, each of which is known to generate toxic compounds associated with increased cancer risk. Within one week after participants began the vegan diet, the activity of all four enzymes in their bodies declined significantly to a 33 to 66 percent lower rate. Two other toxic metabolites declined from 30 to 60 percent within two weeks after participants began the vegan diet. All these favorable changes quickly disappeared when participants resumed the conventional diet. No changes in fecal enzymes and metabolites were observed in members of the control group, who did not change their diets.
Several studies have confirmed the positive effects of vegan diets (mostly raw foods) on gut microflora.142–146 In addition, a number of metabolic changes that occur with vegetarian and vegan diets may provide additional protection against cancer:
• Lower lifetime estrogen exposure. Lower levels and reduced lifetime estrogen exposure are associated with a reduced risk of breast cancer.147–151
• Lower concentrations of potentially carcinogenic bile acids. There are fewer bacteria converting bile acids into more-carcinogenic secondary bile acids. A lower colonic pH also reduces the activity of the enzymes responsible for this unfavorable conversion process.152–157
• Larger, heavier, softer stools resulting in more-frequent bowel movements. Potential carcinogens have less time to harm the intestinal lining.149,152,158,159
• Lower levels of fecal mutagens (substances that damage DNA). Fecal mutagens have less opportunity to damage DNA, reducing risk of colon cancer.160–164
• Reduced oxidative stress. Fewer products of oxidation and increased antioxidant status can protect against DNA damage, possibly decreasing cancer risk.40,43,165–169
It isn’t known for sure what type of plant-based diet provides the greatest protection against cancer, but we do know that whole plant foods are an important part of the answer and that raw vegetables appear to have an advantage over cooked vegetables.
More than two dozen studies have examined the relationship between raw and cooked vegetables and cancer risk. These studies were not done on people who consumed raw vegan diets; rather, they focused on the possible advantages of specific foods or components of foods. While most studies have shown that as vegetable intake increases, cancer risk decreases, the findings have been more consistent for raw vegetables than for cooked vegetables.170
The 2007 WCRF/AICR diet and cancer report cited twenty-three studies that provided separate cancer risk estimates for raw vegetable consumption.131 Of these reports, sixteen showed statistically significant reductions in cancer risk with raw vegetable intake and with increasing rates of consumption. A comprehensive literature review by researchers from Columbia University in New York and the Fred Hutchinson Cancer Research Center in Seattle suggested several reasons why raw vegetables provide even greater protection against cancer than cooked vegetables.170
• Cooking vegetables decreases protective substances, such as vitamin C and phytochemicals, which are watersoluble and heatsensitive.
• Cooking foods disables the enzymes responsible for converting certain phytochemicals to active forms that have powerful anticancer effects (for more on phytochemicals and enzymes, see pages 260 to 263).
• Cooking foods produces changes in the foods’ physical structure and its physiologic effects. For example, cooking may reduce insoluble fiber, decreasing the foods’ ability to bind to cancer-causing substances.
• Cooking foods at high temperatures can cause the formation of compounds that damage DNA, such as acrylamide, heterocyclic amines, polycyclic aromatic hydrocarbons, and advanced glycation end-products (for more on these compounds, see pages 268 to 269).
We also know that raw diets can favorably alter gut microflora, reducing toxic metabolites associated with increased cancer risk. Raw-food preparation techniques can enhance the content of protective substances in foods or the availability of these compounds. For example, juicing removes plant cell walls and phytate that can inhibit absorption of nutrients and phytochemicals, and sprouting increases the nutrient and phytochemical content of foods. (For more on this, see pages 260 and 261.) However, it must be noted that cooking can kill potentially harmful organisms, improve the bioavailability of some nutrients (e.g., carotenoids), reduce antinutrients, and improve the digestibility of some foods, such as protein-rich legumes. Moist methods of cooking, such as steaming, are preferable, because these methods keep products of oxidation to a minimum and keep temperatures at or below 212 degrees F (100 degrees C).
For further information, see Becoming Raw: The Essential Guide to Raw Vegan Diets by Brenda Davis and Vesanto Melina (Book Publishing Company, 2010).
There’s been ongoing debate regarding the effects of soy products on cancer risk, particularly on breast cancer. Soybeans are unique among legumes because they contain phytoestrogens (plant estrogens) called isoflavones that can bind to estrogen-receptor sites. However, plant estrogens aren’t the same as human estrogens and have generally much weaker activity. Plant estrogens are also more selective in the receptors to which they bind; thus, they’re called selective estrogen-receptor modulators. The type of estrogen receptors in different tissues determines whether the isoflavones have weak estrogen-like effects or antiestrogen effects.171
For years, physicians warned patients with estrogen-positive breast cancer to avoid soy products due to concerns that soy phytoestrogens would act like human estrogen and increase cancer cell growth. However, recent research suggests that in reproductive cells (e.g., breast and uterus tissue), isoflavones act more as antiestrogens, while in osteoblasts (bone-forming cells), they behave as weak estrogens—with beneficial effects in both cases.171,172
The evidence to date suggests lifetime soy consumption may actually help protect against breast cancer and improve breast cancer prognosis.173,22 The following is a brief summary of the findings on soy and breast cancer:
• Soy consumption during childhood and adolescence reduces lifetime breast cancer risk.174–178
• A significant inverse association exists between breast cancer risk and soy isoflavone intake in Asian populations—less breast cancer with more soy—although no association has been found in Western populations.178–182
• The inverse association between soy and Asian breast cancer risk is stronger in postmenopausal women than in premenopausal women.180,183
• The soy isoflavone daidzein can be metabolized by bacteria into a compound called S-equol, which may provide added protection, although research is limited. Asian populations have more equol-producing bacteria in their intestines than Western populations. Interestingly, one study reported that vegetarians were 4.25 times more likely to be S-equol producers than nonvegetarians.184,185
• Most studies show the risk of breast cancer recurrence or death from breast cancer is either reduced or unaffected by intake of soy isoflavones, even with estrogen-positive breast cancer and tamoxifen use.186–192 However, one small Korean study found high intake of soy isoflavones (mostly from black soybeans) increased the risk of cancer recurrence in HER2-positive breast cancer patients, although it quite strongly reduced the risk in HER2-negative breast cancer patients.193
• A pooled analysis of both Chinese and American women found that those with the highest intakes (≥ 10 mg isoflavones) were 17 percent less likely to die from breast cancer and 25 percent less likely to have a recurrence of breast cancer.194
• A meta-analysis of Chinese and American studies showed the highest soy food intakes were associated with 16 percent reduced mortality and 26 percent reduction in cancer recurrence, compared with the lowest soy intakes. In postmenopausal women, high soy intake reduced recurrence by 36 percent in ER- cancers and 35 percent in ER+ cancers.195
• Any protective effect soy foods have against cancer appears to be due to their isoflavone content.22,173
• The highest quartile of soy product intake was associated with a 61 percent reduced risk of breast cancer in BRCA1 and BRCA2 carriers (carriers of an inherited mutation that increases breast cancer risk); carriers with the highest quartile of meat intake had almost double the risk of breast cancer.196
The Bottom Line: Soy intake is either protective against breast cancer, or it doesn’t affect risk either way. The risk of breast cancer recurrence and breast cancer death appears to be reduced with soy intake. The evidence of potentially beneficial effects is strongest for moderate intake (two servings a day) of traditional soy foods, such as tofu and soy milk.
Note that soy intake has also been associated with a reduced risk of prostate cancer and reduced prostate cancer cell growth.171,197–199
Based on the evidence currently available, vegans are at an advantage where cancer risk is concerned. There are many steps vegans can take to maximize the benefits of their diet. While it’s still too early to estimate the potential of vegan diets in cancer treatment, consuming a well-planned vegan diet seems a reasonable addition to any treatment program. The following tips help to design a vegan diet that provides the greatest possible protection:
1. Eat mostly whole plant foods. Opt for local organic foods whenever possible.
2. Include at least nine servings of vegetables and fruits daily, emphasizing all the colors of the rainbow and plenty of dark leafy greens.
3. Aim for at least 35 grams of fiber each day from a variety of plant foods.
4. Minimize processed foods, especially those containing refined carbohydrates.
5. Eliminate products containing trans-fatty acids.
6. Rely on whole foods (such as nuts, seeds, and avocados) for most fat intake, ensuring sufficient essential fatty acids. (For more on essential fatty acids, see page 117.)
7. Eat raw foods daily. Sprout foods more often.
8. If cooking, stick mainly to wet cooking methods, such as steaming and stewing.
9. Flavor foods with immune-boosting herbs and spices, such as turmeric, ginger, garlic, basil, oregano, rosemary, and coriander.
10. Make pure, clean water the beverage of choice. Other healthful beverages include fresh vegetable juices and antioxidant-rich teas, such as green tea.
The rate of diabetes occurrence in the United States has increased more than 900 percent in fifty years, from 0.9 percent in the late 1950s to 8.3 percent in 2010, according to the Centers for Disease Control and Prevention (CDC). If current trends continue, the CDC estimates that as many as one in three American adults will have diabetes by 2050.200,201
Diabetes rate among the entire population: 8.3%
Diabetes rate among Americans more than 20 years old: 11.3%
Diabetes rate among Americans more than 65 years old: 26.9%
Estimated prediabetes rate among Americans more than 20 years old: 35%
Estimated prediabetes rate among Americans more than 65 years old: 50%
Source:201
Statistically, diabetes is the seventh leading cause of death in the United States. However, this figure belies the fact that most people with diabetes don’t die of diabetes; instead, they die of heart disease, kidney failure, and other complications associated with diabetes. But the United States isn’t the only nation experiencing this surge. Globally, diabetes has become the twenty-first-century plague, crippling rich and poor nations alike.
Some people believe that type 2 diabetes is more a matter of bad genes than bad habits. Although some populations do have greater susceptibility to the disease, genes serve primarily as a loaded gun; it’s almost always diet and lifestyle that pull the trigger.
The people of the Marshall Islands provide a poignant example. The Marshall Islands lie about 2,300 miles southwest of Hawaii and have a population of about 60,000. Sadly, an estimated 28 percent of Marshallese older than 15—and 50 percent of those older than 35—have type 2 diabetes.
Seventy years ago, diabetes was virtually unheard of there. Although changes in the population’s genes have been negligible since then, dietary and lifestyle changes have been profound. In the 1940s, the Marshallese were slim and physically active and lived off the land and the sea. Their diet included fish and other seafood, as well as edible plants, such as coconut, breadfruit, taro, pandanus, and leafy greens. All of these foods were acquired through physical work, helping the people burn calories and maintain fitness.
Today, the Marshallese people have become largely sedentary, and their diet consists primarily of imported processed foods. It would be difficult to design a diet that could more efficiently induce type 2 diabetes than the diet adopted by the Marshallese. A typical adult’s breakfast consists of cake donuts or sweet pancakes and coffee, while children often start the day with popsicles, chips, soda pop, or dry ramen noodles sprinkled with Kool-Aid. Lunch and dinner feature sticky white rice with meat or fish. Favorite meats are Spam, canned corned beef, chicken, and variety meats, such as turkey tails. Meals are often washed down with a sweetened beverage.
In a laudable effort to reverse the Marshallese diabetes epidemic, Canvasback Missions Inc. (a Christian nonprofit organization that specializes in medical missions to remote South Pacific islands) partnered with Loma Linda University and the Marshall Islands Ministry of Health to launch a lifestyle-based diabetes research study in 2006. Coauthor Brenda Davis served as lead dietitian to design and implement the diet portion of the treatment program.
For each intervention period, approximately half the qualified participants were assigned to an intervention group and half to a control group. Intervention participants received diet and lifestyle instruction over a three- to six-month period, while the control group received standard care (advice from a physician and/or other health care worker to exercise, eat more healthfully, and take the appropriate medication). Control group participants were guaranteed a place in the intervention group once their six-month control period had been completed (although from that point on, their data couldn’t be used in the analysis).
The two key elements of the lifestyle intervention were diet and exercise. The treatment’s primary objective was to overcome insulin resistance and to restore insulin sensitivity as much as physiologically possible. The diet was designed to support blood-glucose control, reduce inflammation, reduce oxidative stress, and restore nutritional status. (For information on the practical implementation of these parameters, see pages 259 to 265). To accomplish this task, these dietary parameters were set:
• whole-foods, plant-based diet
• minimal refined carbohydrates
• minimal ground grains, such as flour
• controlled portions of intact (whole) grains
• very high fiber (40 to 50 grams or more per day)
• emphasis on foods rich in viscous fiber (flaxseeds, oats, barley, beans, guar gum, psyllium seeds)
• moderate fat from healthful sources, such as nuts, seeds, and coconut (20 to 25 percent of total calories from fat)
• low saturated fat (less than 7 percent of total calories)
• zero trans-fatty acids
• sufficient omega-3 fatty acids (fish was permitted)
• high-phytochemical and high-antioxidant foods
• low dietary oxidants
• low glycemic load
• moderate sodium (less than 2,300 mg per day)
The program results were remarkable during the first two to four weeks. Average reductions in fasting blood glucose were more than 70 mg/dL (4 mmol/L), and weight loss averaged approximately 2 pounds (1 kg) per week. Total and LDL cholesterol, triglycerides, and blood pressure plummeted. By twelve weeks, HbA1c (also called A1C or hemoglobin A1c, a measure of glucose control over two to three months) dropped by 2 points and hs-CRP by 1.2 points. Participants consistently reported dramatic reductions or complete disappearance of pain in the legs, arms, and joints. Many noted increased energy, improved mental clarity, fewer nightly trips to the bathroom, and rapid relief of chronic constipation. The majority of participants stopped taking diabetes medications.
After twelve weeks, progress varied according to the participant’s commitment to the program. Those who stuck to the program continued to see improvements. Some completely reversed their disease, eliminating the need for medication and experiencing blood glucose levels well within the normal range. The Marshallese results prove the value of lifestyle interventions based on plant-strong, near-vegan diets.
Plant-based diets have shown positive results in numerous studies. In 2011, researchers undertook an extensive review of epidemiologic and clinical trial evidence worldwide that related dietary patterns, nutrients, and foods to diabetes risk.202 The study authors concluded
“Together with the maintenance of ideal body weight, the promotion of the so-called prudent diet (characterized by a higher intake of food groups that are generally recommended for health promotion, particularly plant-based foods, and a lower intake of red meat, meat products, sweets, high-fat dairy, and refined grains) or a Mediterranean dietary pattern rich in olive oil, fruits, and vegetables, including whole grains, pulses, and nuts, low-fat dairy, and moderate alcohol consumption (mainly red wine) appears as the best strategy to decrease diabetes risk.”202
The observational studies reviewed in this report are briefly summarized in table 2.5. Studies are listed according to publication date, beginning with the most recent. The studies show that the dietary factors most clearly associated with increased risk come almost exclusively from two food categories—animal products and processed foods—and they include red meat, processed meat, high-fat dairy products, trans fats, fried foods, soft drinks, and refined-carbohydrate foods (white flour and sugar-laden products). The dietary factors most strongly associated with decreased risk were plant-based foods or food components, such as vegetables, fruits, whole grains, and fiber.
Although one might expect the occurrence of diabetes to be lower in vegan and near-vegan populations, data was completely lacking until 2009, when the AHS-2 released findings on diabetes rates in various dietary groups.4 Participants in AHS-2 were all Seventh-day Adventists, a group that avoids smoking, uses little alcohol, and is generally health conscious. This means that all the study’s dietary groups share certain health-promoting characteristics.
In this study, more than 60,000 participants had completed fifty-page questionnaires regarding their health status and lifestyle choices at baseline (data collected between 2002 and 2006). One question asked whether the respondent had been diagnosed with diabetes. In the initial 2009 findings, only 2.9 percent of the vegans had been diagnosed with diabetes compared to 7.6 percent of the nonvegetarians (see table 2.6 on page 60).
TABLE 2.5. Observational studies on dietary intake and diabetes risk
Source:202
*PUFA = polyunsaturated fatty acids
A second AHS-2 report followed in 2011, showing the results of a follow-up questionnaire administered to more than 41,000 participants two years after the first questionnaire. It elicited information on the development of diabetes in participants who had had no previous diabetes diagnosis.203 Only 0.54 percent of the vegans developed diabetes during this two-year period, compared to 2.12 percent of the nonvegetarians (see table 2.6).
TABLE 2.6. Rates of diabetes among various diet groups
*The terms “pescovegetarian” and “semivegetarian” describe those who aren’t actually vegetarians, but who eat a predominantly vegetarian diet; pescovegetarians are those who eat a vegetarian diet plus fish; semivegetarians are those who eat meat, poultry, or fish less than once a week but more than once a month.
**Odds ratio (OR): “All factors” is adjusted for age, sex, BMI, ethnicity, education, income, physical activity, television watching, sleep habits, and alcohol use. OR compares the probability that one group will develop diabetes versus the probability that another group will develop diabetes. If a group’s OR is 1.0, then its odds would be the same as the control group (in this case, the nonvegetarians). If a group’s OR is less than 1.0, then its odds of developing diabetes would be lower than the control group.
The data include figures with adjustments for lifestyle factors that can influence results. For example, some of the data is adjusted for multiple factors (“all factors”), including age, sex, BMI, ethnicity, education, income, physical activity, television watching, sleep habits, and alcohol use. These factors are all taken into account to isolate the difference in diabetes incidence most likely due to diet alone. When adjusted for all factors, vegans were 49 percent less likely (OR = 0.51) to develop diabetes compared to nonvegetarians in the 2009 report, and 62 percent less likely (OR = .381) in the 2011 report. Some data is adjusted for all factors except BMI, so both diet and body fat could account for the difference in diabetes incidence. For example, in the 2009 report, when the data was adjusted for all factors except BMI, vegans had a 68 percent lower risk (OR = 0.32) of developing diabetes than nonvegetarians.
Finally, a 2014 study compared diabetes rates in similar health-conscious Taiwanese Buddhist volunteers who consumed vegetarian (near-vegan) and omnivorous diets. After adjustments for age, BMI, education, family history of diabetes, physical activity, smoking, and alcohol consumption, vegetarian (near-vegan) diets were associated with a 51 percent lower risk in men (OR = 0.49), a 74 percent lower risk in premenopausal women (OR = 0.26), and a 75 percent lower risk in postmenopausal women (OR = 0.25).204
Based on the results of these studies, vegan and near-vegan diets provide significant protection against diabetes. Differences in risk remain strong even when BMI and other lifestyle factors are accounted for.
Red and processed meats have been associated with increased risk of diabetes, possibly due to the saturated fat and heme iron in meat or the nitrite and nitrate content of processed meats.203 The advantages enjoyed by vegans and near-vegans are likely due to the combination of higher intakes of whole plant foods and the avoidance of meat.
When the effects of a vegan diet are measured using metabolic markers, its advantages are further clarified. A 2005 US study assessed dietary intakes, insulin sensitivity, and the intramyocellular lipid (IMCL) concentration in vegans (on no special vegan diet) and in matched nonvegetarian controls.205 IMCL is fat that accumulates inside cells, which interferes with the action of insulin and increases insulin resistance. The vegans had significantly lower IMCL in soleus muscle fibers (a primary site of glucose metabolism). The researchers also reported significantly better beta-cell function in vegans, meaning that the insulin-producing beta-cells of the pancreas were doing their job more effectively in vegans than in nonvegetarians. These results suggest metabolic advantages in vegans compared to matched nonvegetarians.
A vegan diet also can provide a distinct advantage for overweight postmenopausal women. A 2005 study by the Physicians Committee for Responsible Medicine (PCRM) randomly assigned 64 overweight postmenopausal nondiabetic women to a low-fat vegan diet or a National Cholesterol Education Program Step II Guidelines diet (NCEP II).206 After fourteen weeks of diet therapy, weight loss was more than 50 percent greater in the vegan group—5.8 kg (12.8 lb)—compared to 3.8 kg (8.4 lb) in the NCEP II group. Fasting glucose dropped by 6.5 mg/dl (0.36 mmol/L) in the vegan group, compared to 1.8 mg/dl (0.1mmol/L) in the NCEP II group. Insulin sensitivity increased 1.1 points in the vegan group compared to 0.3 point in the NCEP II group.
In 2007, a German research team measured the impact of vegan diets on blood glucose levels (glycemic index [GI] and glycemic load [GL]).207 (For more on GI and GL, see pages 172 and 173.) The vegans had very high intakes of dietary fiber, averaging close to 57 grams per day; the average GI of the vegan diets in this population was 51. By comparison, four large studies reported that 20 percent of the general population with the lowest GIs had levels ranging from 64 to 72; the rest had higher GIs.
In addition, the average GL in this vegan population was 144, which is considered low to moderate when compared with observational studies in omnivores. For example, in the Nurses’ Health Study, GLs ranged from 117 to 206. The authors concluded that a vegan diet, including large amounts of fruit, vegetables, whole grains, legumes, and nuts, is characterized by a low GI and GL, relative to nonvegetarian diets. Evidence suggests that this difference could provide an advantage in terms of risk for diabetes, as well as CVD.207
In 2007, another US study reported significantly reduced fasting glucose, fasting insulin, insulin resistance, and inflammation (measured by hs-CRP levels) in participants who ate a raw vegan diet, compared to endurance athletes and those who ate standard Western diets.67
Reports abound of complete reversal of type 2 diabetes using plant-based or vegan diets. Lifestyle programs—such as those offered by the Weimar Center, TrueNorth Health Center, Dr. Joel Fuhrman, Lifestyle Center of America, Tree of Life, Dr. McDougall’s Health and Medical Center, Newstart in Guam, and the Diabetes Wellness Center in the Marshall Islands—have all documented successful reversal in committed participants. Although the program designs vary in their starch, fat, and raw-food content, they share a common foundation of unprocessed, whole plant foods. The diets are consistently rich in fiber, phytochemicals, and antioxidants low in saturated fat and free of trans-fatty acids and cholesterol.
The first report of successful use of a vegan diet for the treatment of diabetes in the United States was published in 1994. Twenty-one patients with known type 2 diabetes and diabetic neuropathy (nerve damage) received treatment for twenty-five days in a residential program; they exercised and ate a low-fat (10 to 15 percent of calories from fat), high-fiber, unrefined vegan diet.
Within four to sixteen days, pain associated with their diabetic neuropathy was completely eliminated in 17 of the 21 patients; although numbness persisted, it improved significantly. Weight loss averaged close to 5 kg (11 lb) during the twenty-five days. Fasting blood glucose dropped, and insulin needs were cut in half. Five participants were taken off their hypoglycemic agents. Follow-up of 17 of the 21 participants indicated that 71 percent remained on the program, and in all but one, relief from diabetic neuropathy continued or further improved.208
Since this time, several trials have been conducted by PCRM researchers and their colleagues to test the effectiveness of low-fat vegan diets (with no caloric restriction) in type 2 diabetes treatment. One study from the Czech Republic compared the effects of a calorie-restricted near-vegan diet (vegan plus no more than one portion of low-fat yogurt per day).209
These randomized controlled clinical trials showed that vegan diets were more effective in treating type 2 diabetes than conventional treatment diets. The initial pilot study (1999) by a PCRM research team found that compared to a prudent conventional treatment diet, the low-fat vegan diet was associated with reductions in body weight, blood lipids, fasting glucose, and HbA1c.210 These results were notable because reductions in oral diabetes medications were greater among the vegans, even though they had no restrictions on calories, carbohydrates, or portions, and their carbohydrate intakes increased.
A second PCRM study, initiated in 2004, followed 99 participants with type 2 diabetes for seventy-four weeks. Forty-nine of the participants were randomized to a vegan diet group and 50 to an American Diabetes Association (ADA) diet group, following the ADA’s 2003 Guidelines. Results of the clinical findings from the first twenty-two weeks of the study were released in 2006.211 Although both groups improved significantly, all markers of diabetes improved to a greater extent in the vegan group than in the control group during this period.
In 2009, the seventy-four-week results were released.212 Although the diet effects were reduced for most clinical markers in both dietary groups compared to the initial findings at twenty-two weeks, generally, the differences between the vegan group and the ADA group were greater at seventy-four weeks. Questions often arise about the acceptability of a vegan diet, so it’s also worth noting that PCRM study participants rated the vegan and ADA diets as being equally acceptable.213
A 2011 report compared the PCRM study group’s GI and GL at twenty-two weeks.214 While GI was lower in the vegan group, suggesting food choices that had a lower overall GI, its GL was higher. GL reflects total carbohydrate intake, and the vegan group had eaten an average of 245 grams per day at twenty-two weeks. In contrast, the ADA group ate an average of only 170 grams of carbohydrate per day. Although in this study, GL was not linked to weight loss or changes in HbA1c, GI was predictive of weight loss—for every point decrease in GI, participants lost about 0.2 kg (0.44 lb). In turn, weight loss was predictive of decreasing HbA1c.
Much of the published literature has emphasized very low-fat vegan diets, but there’s little to support the notion that higher-fat whole plant foods are detrimental for prevention and/or reversal of type 2 diabetes. On the contrary, considerable evidence exists that higher-fat plant foods, especially nuts, may be beneficial. In the Nurses’ Health Study, both nut and peanut butter consumption were inversely associated with diabetes risk, even after adjustments for other risk factors.215 The relative risk of developing diabetes dropped 27 percent for those who ate five or more servings of nuts per week and by 21 percent for those who ate five or more servings of peanut butter per week, compared to those who never or almost never ate nuts.
The Nurses’ Health Study also reported on a subgroup of women with type 2 diabetes and found that those who consumed nuts or peanut butter five or more times a week had a 44 percent reduction in CVD risk and the risk of myocardial infarction (heart attack) compared to those who never or almost never ate nuts or peanut butter.216 It’s thought that the protection provided by nuts is due to their favorable impact on blood cholesterol levels,217 oxidative stress,218,219 markers of inflammation,215,220 and glycemic control.219,221–224
Nuts and other high-fat plant foods have a very low GI and GL, and recent evidence suggests that consuming them attenuates postprandial (after-meal) blood glucose concentrations and insulin response.223,224 Eating nuts with a meal that includes high-carbohydrate foods (potatoes, pasta, rice, or bread) reduces glycemic response—despite an increase in carbohydrate intake (nuts provide small amounts of carbohydrate)—probably because nuts slow the flow of food into the small intestine.223,224
Although most of the research has focused on nuts, seeds would likely provide at least equal, if not greater, benefits. Seeds are higher in protein (12 to 30 percent of calories from protein, compared to 4 to 15 percent in nuts), slightly lower in fat, and generally higher in vitamin E. Seeds also are much higher in essential fatty acids than are nuts (with the exception of walnuts).
Although vegan diets are clearly protective against diabetes, inadequate intakes of vitamins D and B12, which are sometimes at suboptimal levels in vegan diets, may accelerate the progression of diabetes. Recent evidence suggests that many people with diabetes or prediabetes have a reduced vitamin D status, and that a lack of this nutrient can increase the severity of the disease.225
Popular medications used to treat diabetes, such as metformin, may reduce vitamin B12 absorption, further contributing to reduced B12 status and, in turn, increasing homocysteine levels and peripheral neuropathy (nerve damage that causes pain and numbness in hands and feet).226 In scientific review articles, vitamin B12 was found to be an effective treatment for diabetic peripheral neuropathy227 and was perhaps even more effective than standard medications.228
Low omega-3 fatty acid status can increase the risk of depression in people with diabetes.229 Long-chain omega-3 fatty acids seem to be most effective in preventing depression; however, their impact on insulin sensitivity and metabolic control is more tenuous, with clinical trials suggesting marginal or even negative effects.230
Type 2 diabetes is the plague of the twenty-first century. It isn’t spread by viruses or bacteria, but by shifting cultural paradigms that encourage overconsumption and underactivity. Although research that suggests support for vegan diets in the treatment of diabetes is in its early stages, the published data to date offer evidence that whole-foods vegan diets appear somewhat more effective than conventional therapy. Efforts in the Marshall Islands and lifestyle-oriented medical centers suggest that intensive, well-designed vegan diets can reverse the disease in some individuals.
To maximize the potential benefits of a vegan diet in the treatment or prevention of type 2 diabetes, the diet must be based on whole plant foods, such as vegetables, fruits, legumes, nuts, seeds, and whole grains. It’s also important that the diet be designed with care to ensure adequate intakes of all nutrients, especially vitamins B12 and D, and essential fatty acids.
If you ask the average person which food is best for bones, chances are they’ll say milk or dairy products. To most consumers, the popular advertising slogan “Got Milk?” is essentially synonymous with “Got Bones?” People of every age assume it’s risky to shun milk. As it turns out, consumers who eat the most calcium (also the most dairy products) aren’t immune to osteoporosis—in fact, they have higher, not lower, rates of osteoporosis than some populations with far lower calcium intakes.
Although some people consider this proof that dairy products contribute to osteoporosis, the evidence doesn’t bear this out either. There are plenty of studies within populations of consumers who have similar diets and lifestyles but varying dairy intakes. In such cases, dairy consumers tend to have better bone density than nondairy consumers. So what’s going on?
To put it simply, osteoporosis isn’t a “dairy deficiency” disease; it’s not even a “calcium deficiency” disease—it’s a disease that features an impressive interplay of factors. Calcium is important to bone health, but its impact can be augmented by other diet and lifestyle choices, none of which include milk of animal origin.
No one would disagree that cow’s milk is a rich source of calcium (it provides about 300 mg of calcium per cup/250 ml). But that doesn’t make it any more essential for people than moose or deer milk—which, incidentally, have about twice as much calcium as cow’s milk.231 It’s estimated that during the Paleolithic era, when humans had no access to the milk of other species, calcium intakes averaged 2,000 mg per day or more. This calcium came predominantly from wild leafy greens, and some came from other plant foods; none came from animal milk.232
A vegan diet doesn’t guarantee strong bones, but neither does it preclude them. It’s possible to maintain excellent bone health without a single drop of cow’s milk when a diet is well planned. However, research on vegan bone health is somewhat limited to date, and the existing data isn’t particularly encouraging.
Fifteen original studies have examined the bone health of vegans or nearvegans.233–247 Twelve studies assessed the bone mineral density (BMD), bone mineral content, and/or bone width of vegans, compared with measures from lacto-ovo vegetarians and/or nonvegetarian controls.233–244 Two studies reported on both BMD and fracture rates or fracture risk.245,246 One group of researchers reported on the fracture rates in vegans compared to other dietary groups.247
Of the fourteen studies assessing BMD, eight reported significantly reduced indicators of bone health among vegans compared to lacto-ovo vegetarians or nonvegetarians.233–239,246 On average, these studies found that vegan BMDs were 10 to 20 percent lower than those of lacto-ovo vegetarians or nonvegetarians. Six studies found little or no significant difference in the bone health of vegans compared to that of other dietary groups.234,241–245
Of the three studies assessing fracture risk or fracture rates,245–247 one showed increased fracture risk in vegans,246 and the other showed increased fracture rates.247 The first, a study of Taiwanese vegetarians and vegans, estimated the risk of lumbar spine fracture to be 2.5 times higher in long-term vegans (who had been vegan for at least fifteen years) than in other vegetarians and vegans.246 The second, a large UK study that examined fracture rates among various dietary groups, reported 30 percent more fractures in vegans than in other dietary groups.247 The third, a Vietnamese study, found no difference in fracture rates in vegans compared to nonvegetarians.245
No studies have reported significantly better bone health in vegans compared with lacto-ovo vegetarians or nonvegetarians. It’s worth noting, however, that the vegan diets consumed by the participants in these studies generally included few foods fortified with calcium or vitamin D. Today, nondairy beverages are often fortified with calcium and vitamin D; this has been standard practice in North America since the late 1990s. Fortification can be expected to favorably impact vegans’ bone health, and the results of future studies.
When current evidence is examined, it’s clear that vegan diets offer no special protection against bone disease. However, there’s reasonable evidence to suggest that vegans can achieve and maintain excellent bone health. The bone health of older adults reflects lifelong habits not only of diet but also of sun exposure and exercise. When we consider the dietary factors that affect bone health and how these factors are impacted by vegan dietary choices, we can establish ground rules for vegans to build and preserve bone mass throughout life.
Two categories of factors increase the risk of osteoporosis. The first can’t be changed: genetics, family history, advanced age, female gender, and Caucasian or Asian ancestry. The second category comprises behaviors that can change: smoking, heavy alcohol use, physical inactivity, sun exposure, and eating poorly planned diets. Low estrogen or testosterone levels can also increase osteoporosis risk, although these conditions can be treated.
Lifestyle choices have a profound impact on both the quality and quantity of the bones produced and maintained by the body. For example, physical activity—particularly weight-bearing exercise—sends a message to bones to intensify their bone-building efforts, helping to increase bone density during childhood and adolescence248 and to maintain bone density as the body ages.249
The association between food choices and bone health is more complex, and current research findings are inconsistent. Dietary factors known to contribute positively to bone health include appropriate intakes of calcium, iron, zinc, copper, boron, fluoride, magnesium, manganese, and vitamins D, K, and C. Of course, good vitamin D status can also be achieved through adequate exposure to warm sunshine (page 69). Higher consumption of fruits, vegetables,250 and soy may provide protection by inhibiting bone breakdown.251,252
Phosphorus is an important structural mineral for bones; however, diets very high in phosphorus (i.e., more than 3 to 4 grams per day) and low in calcium may upset the calcium balance and weaken bones.253,254 And, although protein has generally been found to be protective, very high protein intakes may be detrimental, particularly when calcium intakes are low.255 Excess protein—especially animal protein—increases metabolic acid load and calcium excretion. If calcium intakes aren’t sufficient to compensate for these losses, a negative calcium balance can result (page 68). Vegan diets tend to produce a lower metabolic acid load, reducing urinary calcium excretion.256 However, vegan diets often are lower in calcium, which can also have negative consequences for bones.
Dietary Factors that Adversely Affect Bone Health Vegans generally don’t consume preformed vitamin A because it’s not present in plants, and they often have lower intakes of sodium, alcohol, and caffeine. As a result, they may be protected from the adverse effects these dietary factors can have:
• Sodium. Sodium and salt increase calcium excretion through urine and perspiration.
• Caffeine. Caffeine appears to reduce the absorption of calcium; however, the effect is completely mitigated by a small increase in calcium intake. For example, adding milk to coffee compensates for the modest reduction in calcium absorption caused by the caffeine content.232 (Fortified soy milk might be expected to do the same.)
• Alcohol. Chronic excessive alcohol consumption reduces calcium and vitamin D absorption and can injure the liver, impairing the body’s ability to activate vitamin D. Alcohol also can decrease estrogen production, eroding a woman’s bone-building capacity.257,258
• Vitamin A. Preformed vitamin A or retinol (the type available in animal products and some supplements) is necessary for bone growth. However, very high intakes can increase bone breakdown and interfere with vitamin D’s role in enhancing calcium absorption. Provitamin A from plants (e.g., beta-carotene) doesn’t have this effect.258,259
Excess preformed vitamin A can have adverse effects at various stages of the life cycle. Because excess vitamin A can be harmful to their babies, it’s recommended that pregnant women avoid very rich sources of vitamin A, such as animal liver and other organ meats.260 The Tolerable Upper Intake Level (UL) for vitamin A is set at 3,000 mg retinol equivalents (RE) per day; a single 3.5-ounce (100 g) serving of beef liver contains nearly 9,600 RE vitamin A. For postmenopausal women at risk for bone fracture, the Institute of Medicine (IOM) advises restricting intake of preformed vitamin A even further, to 1,500 mg RE per day, because excessive intakes can further compromise bone strength.260,261
Numerous dietary factors positively affect bone health, and vegans generally have higher intakes of a long list of these, including potassium, vitamin K, vitamin C, folate, fruits, vegetables, and possibly soy foods. On the other hand, they tend to have lower intakes of calcium, vitamin D, and protein. These nutrients are all critical to the maintenance of bone homeostasis. The three nutrients of concern to vegan bone health (calcium, vitamin D, and protein) have been the source of major controversy among vegan advocates.
There’s no question regarding the importance of calcium for bone health. The facts are clear: calcium is the predominant structural mineral in bones, and it’s necessary for both building and maintaining bone tissue. Calcium also is critical to the body’s proper functioning and is tightly controlled in the blood. If dietary calcium isn’t available in a sufficient quantity to maintain blood calcium levels, additional calcium is quickly mobilized from bones to avert disaster. However, this mobilization can lead to osteoporosis if bones transfer excessive amounts of calcium to the bloodstream.
Should vegans be concerned? When existing data on the bone health of vegans is examined, about two-thirds of the studies suggest a positive association between calcium intake and bone mineral density; the remainder don’t report a significant benefit from higher calcium intake. Of two studies examining fracture rates, one study on Asian participants found calcium intakes in nonvegetarians were almost double that of vegans, but differences in fracture rates were insignificant (5.7 percent in vegans and 5.4 percent in nonvegans). In this study, the rate of bone loss was actually lower in the vegans (-0.86 percent per year in vegans compared to -1.91 percent per year in nonvegans).245
The second study, EPIC-Oxford, reported a 30 percent increase in fracture rates in UK vegans compared to other dietary groups in the United Kingdom.247 However, about 45 percent of the vegans had calcium intakes below 525 mg per day, while less than 6 percent of those in other dietary groups (lacto-ovo vegetarian, fish eaters, and nonvegetarians) had intakes that low. When only participants who averaged more than 525 mg of calcium per day were compared, the vegans had about the same rate of fractures as other dietary groups (fracture rates were the same as those of meat eaters and slightly lower than those of lacto-ovo vegetarians and fish eaters).
Based on comparisons of this limited data, it’s possible that Caucasian vegans may need more dietary calcium than Asian vegans. This could be related to genetics or bone structure, dietary practices, or lifestyle factors, such as sun exposure or weight-bearing activities.
This somewhat ambiguous and unpredictable relationship between calcium and bone health isn’t unique to vegan populations. Some nonvegetarian populations whose average intake is less than 400 mg of calcium per day have lower rates of osteoporosis than populations who average more than 1,000 mg of calcium per day.
Two meta-analyses (one on premenopausal women262 and one on postmenopausal women263,264) reported a weak positive correlation between calcium intake and bone mineral density. The meta-analysis on thirty-three studies of premenopausal women reported a 13 percent increase in bone mineral density in those with higher calcium intakes.262 The authors suggested that calcium supplementation of approximately 1,000 mg per day would prevent a loss of 1 percent of bone per year at most bone sites in premenopausal women. The meta-analysis on postmenopausal women found that supplementation with 500 to 2,000 mg of calcium per day provided a 2.05 percent increase in total-body bone density.263,264
Two additional meta-analyses examined the relationship between calcium intake and fracture rates, and found no significant benefit conferred by increased calcium intake. The first analysis found no obvious reductions in hip fracture risk after the addition of 300 mg increments of daily calcium in more than 28,511 postmenopausal women.265 The second analysis found that dietary calcium intake wasn’t significantly associated with a lower hip fracture risk in men or women (although there was a small but insignificant benefit with higher intakes in men).266 Surprisingly, in this meta-analysis, calcium supplements weren’t associated with risk reduction for nonvertebral fractures and instead were actually associated with a 64 percent increase in risk of hip fractures.266
The calcium conundrum begins to unravel when we recognize that calcium intake isn’t the only determinant of calcium balance (the net of calcium absorption and calcium excretion)—and it’s not even the most important. One research team reported that only 11 percent of calcium balance is determined by calcium intake and 15 percent by calcium absorption; 74 percent is determined by calcium excretion (51 percent urinary excretion and 23 percent fecal excretion) and 15 percent by calcium absorption.22 If a diet compromises calcium absorption and enhances calcium excretion, calcium intakes need to be high enough to compensate for these losses. On the other hand, if the diet maximizes absorption and minimizes excretion, dietary calcium requirements would be considerably lower.
Vegan diets can be carefully constructed to support calcium balance, but many vegans tend to fall short in calcium intake. When all other dietary factors are equal, higher calcium intake appears to provide protection to vegans. How much calcium do vegans need? It all depends on how well designed the diet is and on other lifestyle factors, such as physical activity. As noted above, there’s good evidence that calcium intakes below 525 mg daily can jeopardize bone health in vegans. Until more-definitive research is released, it’s wise for vegans to meet recommended calcium intakes. (For more information on calcium, see pages 182 to 186).
Vitamin D is no minor player in contributing to bone health. When blood levels of calcium begin to drop, the body converts vitamin D into its active form to enhance calcium absorption and utilization and reduce calcium losses. Considering the contribution made by calcium absorption and excretion to overall calcium balance, it’s easy to understand why vitamin D is every bit as relevant to bone health as calcium.
Unfortunately, vegans consistently consume less vitamin D than nonvegetarians. In addition, people who live in cool climates or who don’t get enough exposure to sunshine frequently fall short of ideal vitamin D levels. Historically, humans derived vitamin D from sunshine because, apart from fatty fish, very few foods were reliable vitamin D sources. As humans migrated further from the equator, clothed themselves, protected themselves from the elements by staying indoors, and later, lived in smog-filled cities, vitamin D deficiency became widespread. Health authorities responded by adding vitamin D to a basic staple—cow’s milk. Although many types of nondairy milk are now fortified with similar amounts of vitamin D, total intakes from these sources generally aren’t sufficient for vegans to meet their dietary requirements for vitamin D.
As a result of extensive evidence of health benefits associated with higher intakes, in 2010 the IOM issued new dietary reference intakes (DRI) for vitamin D. The Recommended Dietary Allowance (RDA) was increased by 50 percent to 15 mg (600 IU) for everyone from ages 1 to 70 and 20 mg (800 IU) for people older than 70.
In spite of this significant increase in DRI, many experts believe that a higher intake—25 to 50 mcg (1,000 to 2,000 IU) per day—is required to minimize the risk of vitamin D-related diseases and disorders. It seems reasonable for vegans to aim for this target, particularly if their exposure to warm sunshine is limited. (For more on vitamin D, see pages 222 to 230).
For many years, a common belief among vegans was that eliminating animal protein protected against osteoporosis. Epidemiological evidence added weight to this argument because osteoporosis rates were higher in developed nations with high animal protein consumption, even when calcium intakes were high.
The standard theory was that animal protein is rich in amino acids that raise the acidity of blood. Since blood pH is tightly maintained, such acids must be neutralized. The body has a huge alkaline reserve to do this job—the calcium in bones. Once this calcium neutralizes excess blood acid, it’s excreted in urine. As a result, it was thought that over time, high intake of animal protein leads to bone loss and osteoporosis.
Given this association between animal protein and calcium loss, it follows that vegans should enjoy protection against osteoporosis and likely require less dietary calcium than meat eaters. Although logical, this theory hasn’t been supported by scientific research. As it turns out, the connection between protein and bone health is a little more complicated. In addition, the data on vegans’ bone health isn’t as favorable as would be expected if the animal protein hypothesis were accurate.
Although some studies have linked high protein intakes with negative calcium balance,268 lower bone mineral density,269 and increased fracture rates,270 others have reported better bone density271 and reduced fracture risk.272,273 Additional systematic reviews and meta-analyses have either found no clear association between protein intake and fracture risk or found a slightly favorable protein effect.274,275 There is, however, some evidence that acid-forming diets may have an adverse effect by suppressing bone-building activity and stimulating bone breakdown.1
It appears as though protein promotes some metabolic activities detrimental to bone health while simultaneously supporting others that benefit bone health. How can this rather confusing and contradictory relationship be explained? We know that high protein intakes induce urinary calcium losses. However, these losses are less significant when protein is consumed as part of a whole food, rather than as an isolated or concentrated protein supplement. Although urinary calcium losses were long thought to be due to the metabolic acid load induced by dietary protein, more-recent evidence suggests that other mechanisms may be involved.276
Dietary protein has been shown to increase calcium absorption as well as enhance bone-building activities. When the positive and negative impacts of protein are weighed, it appears that protein generally provides modest protection for bones, particularly when calcium intake is adequate and fruit and vegetable consumption is sufficiently high.277
For vegans, getting sufficient protein appears to be an important piece of the bone-health puzzle. This message was strongly supported by a recent research study that reported the risk of wrist fractures in a group of 1,865 women followed for twenty-five years. Among the 40 percent of study participants who were vegetarian, those with the highest intakes of protein-rich plant foods (e.g., legumes, meat analogs, and nuts) had the lowest risk of wrist fracture. Those who ate fewer than three servings of protein-rich plant foods per week had the highest risk of wrist fracture.278
The weight of the evidence suggests that vegans need to be as concerned about long-term bone health as people of other dietary persuasions. This means a vegan diet needs to be designed with attention to the myriad factors that work for or against bone health.
Vegan diets can offer a number of advantages over omnivorous diets where bone health is concerned. The features of vegan diets that appear most protective are:
• Higher in fruits and vegetables. Vegans have higher intakes of vegetables and fruits than nonvegetarians.
• Lower in sodium. Vegans tend to eat more whole foods and use fewer processed foods (77 percent of dietary sodium comes from processed foods), thus their total sodium intakes may be reduced.
• Lower in alcohol and caffeine. Vegans tend to consume less alcohol and caffeine, both of which can contribute to bone loss.
• Higher in bone-friendly vitamins, such as vitamin K, vitamin C, and folate.
• Higher in bone-building minerals, including potassium, magnesium, and boron.
• Higher in soy foods and the potentially protective isoflavones they contain.
• Adequate in protein, without being excessive.
• More alkali-forming than nonvegetarian diets.
Conversely, poorly planned vegan diets can undermine bone health. Vegans must recognize and avoid common pitfalls:
• Very low calcium intakes (less than 525 mg per day). While some populations appear to maintain reasonable bone health despite relatively low calcium intakes, the average Western vegan seems to require higher amounts of calcium.
• Insufficient vitamin D from sun exposure or fortified foods.
• Too little protein. Protein intakes at lower-than-recommended levels can be detrimental. Protein is an essential bone component; it boosts calcium absorption and increases bone formation.
• Inadequate energy intakes. A lack of calories can lead to underweight (more common among vegans), a risk factor for osteoporosis.
With a well-designed diet, however, vegans can enjoy excellent bone health throughout their life cycle. Meeting nutritional requirements, not smoking, and moderating alcohol and caffeine intake also are invaluable contributors to lifelong bone health. In addition, regular weight-bearing exercise sends a powerful signal to bones to build osteoblasts and strengthen the skeleton. For practical tips on building and maintaining strong, healthy vegan bones, see “Solid Solutions for Better Bones” on page 185.
Researchers have examined the relationship between specific dietary patterns and risk for developing a variety of other diseases. In these studies, people who eat vegan and other types of vegetarian diets are compared to similar health-conscious nonvegetarians, or in some cases, to people who eat standard Western fare. Although the evidence is currently limited, vegan diets have been associated with risk reduction and/or effective treatment of cataracts, gallstones, fibromyalgia, kidney disease, diverticular disease, hypothyroidism, and rheumatoid arthritis. The risk of developing dementia may increase or decrease with vegan diets, depending on several factors.
Globally, cataracts are the leading cause of blindness, and the risk of developing cataracts increases with age. In 2011, EPIC-Oxford reported a strong correlation between meat intake and cataract risk; risks decreased progressively from high meat eaters to low meat eaters, fish eaters, vegetarians, and vegans.279 This study examined data on 27,670 participants (all over 40 years of age) followed for at least fifteen years. After adjustments for many variables, the study showed that compared to high meat eaters, vegans had a 40 percent reduction in the risk of developing cataracts. Although this study doesn’t prove that eating meat causes cataracts, it certainly suggests an association that warrants further investigation.
Based on headlines in the popular press several years ago, rumors about tofu began to circulate, alleging that tofu caused dementia and that a vegan diet could be detrimental to brain health. As evidence emerged, it became clear that the risk of developing dementia may indeed be greater for vegans who have suboptimal B12 status, but actually lower for vegans who have good B12 status.
In 1993, findings from AHS-1 suggested that dementia increased with meat consumption.280 In this study, two separate cohorts were examined. In one investigation, vegans and lacto-ovo vegetarians were matched for age, gender, and zip code with people who consumed generous amounts of meat. The subjects who ate meat, poultry, and fish were more than twice as likely to develop dementia as their vegetarian or vegan counterparts.
The second investigation didn’t match subjects. Results showed no significant difference among the vegans, vegetarians, and nonvegetarians in the incidence of dementia, although there was a trend toward delayed onset in the vegetarians and vegans.
In 2013, AHS-2 released its initial findings on neurologic disorders (e.g., Alzheimer’s and Parkinson’s disease). Vegetarians (including vegans) had a 7 percent risk reduction compared to nonvegetarians; there was a 14 percent lower risk for men, although the findings weren’t statistically significant.
There are many reasons why these findings showed vegetarians and vegans could be protected from developing dementia. People who eat plant-based diets are less obese, have lower blood cholesterol levels, and are less likely to have hypertension, all factors that may help to protect the brain. In addition, plant-based diets often contain higher levels of the phytochemicals and antioxidants shown to benefit the brain.
However, less favorable results were reported in UK vegetarians in the Oxford Vegetarian Study.281 Although there were only thirty-six deaths from mental and neurological diseases, the study reported vegetarians had 2.2 times more deaths from such dementia-related illnesses than nonvegetarians. Although the reason for this difference isn’t known, suboptimal B12 status in the vegetarians is the most likely explanation.
It’s well recognized that poor vitamin B12 status can contribute to memory loss and brain dysfunction. Four literature reviews from 2000 to 2011 reported significant positive associations between suboptimal B12 status, elevated homocysteine, and rates of dementia and Alzheimer’s disease.282–285 A fifth meta-analysis in 2008 found that vitamin B12 supplementation improved cognition in elderly individuals who had elevated homocysteine but no diagnosed dementia. Unfortunately, vitamin B12 supplementation provided no benefit to those who already suffered from dementia or Alzheimer’s disease.286
In 2000, a study that followed more than 3,000 Japanese adults living in Hawaii reported that those who ate the most tofu during the period between their mid-40s and mid-60s were 2.4 times more likely to experience a decline in cognition during their 70s to 905.287 The results sent shock waves through the vegan world.
Unfortunately, the headlines didn’t mention that the data on food intake was collected only twice—during the participants’ mid-60s (baseline) and their early 70s—and for a limited number of foods. Cognitive function wasn’t measured until about twenty years later. It’s possible that food choices made during this period of twenty years played a larger role than the tofu eaten decades before. There was also some suggestion that those with higher midlife tofu intake came from poor immigrant families that were less able to provide adequate nutrition during the early years of childhood. Regardless, the findings generated interest within the scientific community, as well as further research.
In a study of Japanese-American seniors (65 and older) released the same year, tofu intake was very weakly linked to lower cognition scores, but only among women using estrogen replacement therapy, and only at baseline.288 After two years of follow-up, it turned out that tofu consumption wasn’t associated with cognitive decline in men or women (regardless of the use of hormone replacements).
In 2008, a study from Indonesia reported that tempeh consumption was associated with slightly improved memory scores, while tofu consumption yielded slightly reduced scores. The authors suggested that the most plausible explanation for the difference was due to production methods used in Indonesia; formaldehyde was commonly added to tofu but not to tempeh.289 In 2010, the same investigators revisited the tofu/cognition relationship in participants between the ages of 56 and 97. They found that eating both tofu and tempeh improved immediate recall in relatively younger participants with an average age of 67, but that the association was no longer significant in older participants who averaged 80 years of age.290
Although these later studies allayed the fears of some consumers, other studies have provided additional reassurance. To date, approximately thirteen clinical studies have tested the link between soy and cognition. Of these, ten studies found soy consumption beneficial291–300 and three reported that soy consumption is neither beneficial nor detrimental.301–303 None of the clinical trials confirmed a causative effect between soy consumption and cognitive decline.
The message is that becoming vegan could either impair or enhance memory—it all depends on diet and lifestyle choices. Ensuring a daily reliable source of vitamin B12 is crucial to optimal brain function. Vegan seniors who take B12 supplements could actually be at an advantage in this regard, because animal products are unreliable B12 sources in people older than 50 (for more on vitamin B12, see pages 214 and 222.
Folate and vitamin B6 also are important; however, these nutrients are generously available in most vegan diets. As an added bonus, vegans tend to have high intakes of antioxidants and phytochemicals, which appear to protect brain health. Of course, vegans who are physically active, get sufficient rest, avoid smoking and excessive alcohol, and keep their brains active and challenged further reduce their risk of cognitive decline.
Diverticular disease is an umbrella term that includes two diseases of the colon—diverticulosis (small pockets or pouches in the colon) and diverticulitis (inflamed or infected pockets or pouches). Often, diverticulosis goes unnoticed or causes fairly minor symptoms, while diverticulitis is generally more severe, with symptoms ranging from mild bloating and gas to debilitating abdominal pain, vomiting, diarrhea, and fever.
Although diverticular disease is rare in rural Africa and other areas where high-fiber unprocessed diets are standard fare, this painful condition is endemic in the Western world. Risk increases with age, and some studies suggest that as many as 60 percent of those older than 70 are afflicted.304 In 1971, a research team released a seminal report suggesting that diverticular disease is essentially a result of fiber deficiency.305
An impressive body of evidence lends support to that theory.306–308 In 1979, a British study reported that the risk of diverticulitis in vegetarians was only about half that of nonvegetarians. Interestingly, the vegetarians in this study consumed about twice as much fiber as the nonvegetarians.309
In 2011, results released from the EPIC-Oxford study compared the rates of diverticular disease among various dietary groups. The study cohort included 47,033 men and women, 15,459 of whom were vegetarian or vegan (about one-third of the cohort). Of these participants, 812 developed diverticular disease during follow-up. Compared with the meat eaters, when all confounding factors were adjusted for, the risk of developing diverticular disease was 27 percent lower among the lacto-ovo vegetarians and 72 percent lower among the vegans (it’s important to note that only four vegans developed the disease). In this study, the risk of diverticular disease also was inversely associated with dietary fiber intake. Compared with the lowest-fiber consumers (men and women who ate less than 14 grams daily), the highest-fiber consumers (more than 25.5 grams daily for women and 26.1 grams daily for men) had a 42 percent lower risk for diverticular disease.310 (For more on vegans’ fiber intake, see pages 152 to 161.)
Although some studies have found a positive association between meat intake and diverticular disease,306,307,311 the EPIC-Oxford study failed to show a significant association between the amount of meat consumed and the incidence of diverticular disease among the meat eaters. The authors suggested that meat intake in this relatively health-conscious group was too low to influence the risk of disease (they averaged about 3 ounces/90 grams per day), or that the range of intake was too small to detect a significant association. Although high meat intake is often associated with low fiber intake, meat consumption also negatively affects fecal flora. This can reduce the integrity of the colon wall, causing it to weaken and become more prone to developing the pouches or pockets associated with diverticular disease.310
Gallstone formation is one more condition commonly regarded as the product of Western dietary habits. To date, no studies have examined the rate of gallstone formation in vegans; however, there’s good evidence to suggest that a vegan diet may provide some degree of protection.
In 1985, a study of 800 women ranging in age from 40 to 69 reported that nonvegetarians had more than double the risk of developing gallstones than vegetarians,312 even after controlling for confounding variables. A research team from Germany also reported in three small studies a significantly reduced incidence of gallstones among vegetarians compared with nonvegetarians,313–315 although a fourth study showed no significant difference.316
A twenty-year study of 80,898 women (the Nurses’ Health Study) reported that higher long-term intake of vegetable protein was associated with a reduced risk of cholecystectomy (surgical removal of the gallbladder).317 A separate evaluation of the same group of women noted a favorable effect of fruit and vegetable consumption on the risk of gallstone formation.318 A third study with the same women319 found significant risk reductions in women who ate 5 ounces or more of nuts per week compared with participants who ate no nuts. The same team of investigators reported similar benefits in a large cohort of men.320
Although questions remain, a number of dietary factors are known to influence the risk of gallstone formation. Overeating (leading to overweight or obesity) is strongly linked to increased risk.321 High intake of saturated fat, trans-fatty acids, cholesterol,322–324 and refined carbohydrates325 also is thought to increase risk. Conversely, dietary fiber intake,326,327 fruit and vegetable consumption,318 vegetable protein intake,317 and unsaturated fat intake328 are all associated with decreased risk.
Of all dietary patterns, a vegan diet has the lowest risk of overweight and obesity; the lowest intake of saturated fat and cholesterol; and the highest intake of fiber, vegetable protein, fruits, and vegetables. Thus, although definitive data is currently lacking, it’s reasonable to assume that vegans’ risk of developing gallstones would be even lower than that of lacto-ovo vegetarians.
In 2013, AHS-2 released the first report to compare rates of renal disease in vegetarians (including vegans) relative to nonvegetarians. The vegetarians had a 52 percent lower risk of renal disease than similar health-conscious nonvegetarians, and the findings were statistically significant.23
High-protein diets are known to accelerate renal function decline in people with chronic kidney disease (CKD).329 Traditionally, patients with advanced CKD have been advised to consume low-protein diets (no more than 0.6 grams per kilogram of body weight), and that what little protein they’re allowed should come mostly from animal products that contain high-quality protein, such as eggs, meat, poultry, and fish. The general rule of thumb was that at least three-quarters of CKD patients’ limited protein intake come from animal sources and no more than one-quarter from plant sources. In addition, sodium, potassium, phosphorus, and fluids are restricted in an effort to reduce the buildup in blood of toxic waste products that occur when kidney function is compromised.
Vegan diets were considered highly inappropriate for people afflicted with kidney disease. However, interest in plant-based diets began to grow with the recognition that vegan diets—which are low in saturated fat, cholesterol-free, and high in fiber—produced significant improvements in blood lipids, blood pressure, and atherosclerosis, all of which can worsen kidney disease.
The preponderance of evidence suggests that diets rich in vegetable protein don’t promote renal decline to the same extent as diets rich in animal protein (specifically meat-based protein).329 Although both animal and vegetable protein sources can cause renal injury and accelerate CKD, plant-based diets provide more moderate, though adequate, amounts of protein.
One research team reporting on two clinical trials found that consuming protein from plant sources resulted in less protein in the urine and less renal damage than eating animal protein, and that these changes were independent of total protein intake.330,331 The authors concluded, “Protein-modified, rather than protein-restricted, diets may prove advantageous in the long-term treatment of chronic renal failure.”
A second team investigated the impact of shifting patients who had mild renal failure from an unrestricted-protein or conventional low-protein diet to a special vegan diet that included added essential amino acids.332 The authors suggested that the vegan diet would be a suitable replacement for the conventional low-protein diet in patients with mild chronic renal failure. Subjects on the vegan diet showed benefits similar to those provided by the conventional low-protein diet—lowered glomerular filtration rate, improved acid-base balance, and a slower progression of the disease. However, the vegan diet had additional positive features, including less saturated fat, no cholesterol, and lower net acid production when compared to a nonvegetarian low-protein diet. Study participants also considered the vegan diet more economical and palatable than the conventional low-protein diet.
Finally, a 2014 study reported that pregnant women with stages 3–5 CKD who followed vegan or vegetarian low-protein diets and used supplements reduced their risk of having a baby that was small for its gestational age—without detrimental effects on kidney function or proteinuria in the mother.333
Controlling excess dietary phosphorus intake also is a key strategy in CKD management; protein-rich foods are the main source of phosphorus. Investigators of a short-term study that compared diets containing equal phosphorus concentrations from plant versus animal foods reported that plant sources of phosphorus have fewer adverse effects on phosphorus levels in CKD patients than those from animal sources.333 The study authors stated, “These results, if confirmed in longer studies, provide rationale for recommending a predominance of grain-based vegetarian sources of protein to patients with CKD. This will allow increased protein intake without adversely affecting phosphorus levels.”334
The interesting advantage of plant-based diets concerns the form of phosphorus consumed. Organic phosphorus comes from whole foods (both animal and plant foods), while inorganic phosphorus is found in processed foods. Inorganic phosphorus (such as phosphorus added to soft drinks and processed cheese) is essentially fully absorbed by the body. However, the body must convert organic phosphorus to inorganic phosphorus before it can be absorbed. As a result, 40 to 60 percent of the total phosphorus in protein-rich animal products is absorbed.335 In contrast, the phosphorus in plant foods—some of which is in a form called phytate—may be absorbed at a rate of only 20 to 50 percent,335 allowing better control of phosphorus intake. (For more on phytate, see page 181.)
Finally, it’s been suggested that plant-based diets provide an additional advantage to overweight or obese CKD patients. These diets tend to be less energy dense and higher in fiber, and have been associated with more healthful body weights. As stated in the ADA position on vegetarian diets, “Soy-based vegan diets appear to be nutritionally adequate for people with chronic kidney disease and may slow progression of kidney disease.”1
In 2013, the AHS-2 released findings on the risk of hypothyroidism among various dietary groups. Prevalence among vegans was 11 percent lower than among nonvegetarians, although it was 9 percent higher among lacto-ovo vegetarians (statistical significance was not attained). In addition, vegans had a 22 percent lower risk of developing hypothyroidism compared to nonvegetarians. Incident hypothyroidism was positively associated with female gender, white ethnicity, higher BMI, and higher education.336
Although vegan diets are associated with reduced BMI, which is protective, the advantage for vegans was present even after controlling for BMI and other confounding variables. These findings were somewhat surprising, because vegan diets tend to be higher in goitrogens (such as cruciferous vegetables and soy products) and may also be lower in iodine. However, little evidence exists to suggest that goitrogenic foods are a problem when iodine intakes are adequate, so it’s possible that this population has a sufficient, reliable source of iodine in the daily diet (possibly iodized salt or kelp).
Rheumatoid arthritis (RA) is an autoimmune disease that causes chronic inflammation of the joints, the tissues around joints, and the vital organs. Autoimmune diseases occur when the body mistakes its own tissues for foreign intruders and produces antibodies to attack and destroy them. RA can result in severe pain in, damage to, and degeneration of muscles, joints, cartilage, and internal organs. As the disease advances, bones also can erode, resulting in significant deformity. Although research suggests that dietary intervention may serve as an effective treatment option for some RA patients, most trials to date have been small and of short duration, reducing the value or statistical significance of their findings. Still, the results are encouraging.
Seven studies conducted by research teams in Finland have reported the favorable effects of living-food vegan diets (raw diets rich in probiotics and enzymes) on RA patients.337–343 Study participants reported significant reductions in pain, morning stiffness, swelling of joints, and other RA symptoms. More-modest benefits were observed in laboratory markers of the disease (blood tests, urine tests, and X-rays). A variety of additional positive health outcomes were noted in study participants, including favorable changes in fecal flora, reduced blood cholesterol levels, and increased concentrations of protective antioxidants.
Two studies by a team of Swedish investigators examined the impact on RA patients of a gluten-free vegan diet compared to a well-balanced nonvegetarian diet.344,345 In the first study, after one year of treatment, 40.5 percent of those in the vegan group had marked improvement in their disease (fulfilling a standard measure called the ACR20 improvement criteria); only 4 percent of those in the nonvegan group showed improvement.344 The second study focused on changes in blood lipids in RA patients. In the vegan group, total cholesterol, LDL cholesterol, and oxidized-LDL cholesterol declined (as did BMI); levels of triglycerides and HDL cholesterol didn’t change. Markers of inflammation also improved substantially in the vegan group. For these RA patients, the gluten-free vegan diet proved both cardioprotective and anti-inflammatory.345
One US team investigated the effects of a very low-fat vegan diet on participants with RA. Although this study lacked a control group, measures of RA symptoms in participants significantly decreased, with the exception of the duration of morning stiffness. Body weight and C-reactive protein (a measure of inflammation) were also reduced.346
A number of studies have tested variations of plant-based diets, with some including periods of fasting before introduction of the plant-based regimen.347–359 Although the outcomes were variable, favorable changes in fecal flora, reduced pain and stiffness, and improvements in measurable RA indicators were reported.
Vegan diets have many mechanisms that could produce improvements in RA symptoms. The vegetables, fruits, and other whole plant foods that form the basis of vegan diets are key sources of protective anti-inflammatory and antioxidant compounds.360 These diets are free of animal products, including red and processed meats, and are typically low in processed foods, all of which have been associated with inflammatory compounds.361,362 (There’s evidence that animal products increase some individuals’ risk of developing RA,363,364 although a recent study refutes these findings.365)
One study noted that intakes of anti-inflammatory phytochemicals, such as quercetin (found in onions and apples), kaempferol (found in tea and broccoli), and myricetin (found in walnuts and grapes), were more than ten times higher in vegan diets compared to nonvegetarian control diets. Blood carotenoids also measured two to six times greater in living-food vegans than in nonvegetarian controls.338
Another study reported a significant drop of markers of inflammation present in feces.341 The greatly increased fiber intake associated with vegan diets promotes regularity and reduces the time available for harmful compounds to be absorbed from the gut into the bloodstream.338 These advantages disappear when participants resume their usual diets.
Researchers have also observed that when a vegan diet is adopted, it favorably alters the balance of microflora or bacteria that live in intestines.338–341,343 It’s been noted that fecal flora in RA patients are significantly altered compared to controls.366 The mechanism by which intestinal flora are thought to impact RA progression is that some of their harmful breakdown products can pass from the intestine to the bloodstream, behaving like foreign invaders. The body responds by manufacturing antibodies to attack these “foreign invaders,” but in some cases, these antibodies also attack healthy tissue.338
Another popular theory regarding the success of all types of plant-based diets in reducing symptoms of RA is that such diets generally result in weight loss, causing less stress on painful joints. A team of investigators tested the support for this theory by pooling the results of three studies, each using a different type of plant-based diet (vegan, lacto-ovo vegetarian, and a Mediterranean diet) in RA treatment.367 For all the diets, the average weight loss was 2.4 kg (5.3 lb) per person during a trial period of three to four months. When investigators analyzed changes in body weight versus changes in RA symptoms, no significant correlation was observed between weight loss and improvements in RA. Although this doesn’t rule out the possibility that weight reduction is helpful in decreasing RA symptoms, it suggests that the diets provide positive effects outside of weight loss.
For example, some experts argue that benefits conferred by vegan diets are due to removal of food items that produce allergies and aggravate sensitivities in RA patients.368 Common triggers, such as dairy products, eggs, and fish, are eliminated, and many vegan diets eliminate wheat and other gluten-containing grains, nightshades, and citrus fruits, as well. Any diet that excludes these triggers may prove advantageous for people who are sensitive to those particular foods. However, many individuals with RA also appear to benefit from vegan diets, even when gluten-containing grains and nightshade vegetables are included.
Regardless of the mechanisms of their action, for some RA sufferers, vegan diets appear to offer significant benefits. Limited evidence suggests that raw or living-food diets can be especially effective. However, larger longer-term studies are needed before these findings can be confirmed.
