America is a constipated nation . . . If you pass small stools, you have to have large hospitals.
Carbohydrates are packages of solar energy, created by plants through photosynthesis and stored by them after conversion to sugar molecules that become linked in a variety of ways. The main source of energy (calories) for the body, carbohydrates are the preferred fuel for the brain, nervous system, and red blood cells.
Accordingly, carbohydrate-rich plant foods are the most valuable sources of food energy in the human diet. With the exception of dairy products, foods derived from animals contain few or no carbohydrates. Carbohydrate-rich whole plant foods reduce hunger, control blood glucose and insulin metabolism, and keep cholesterol and triglyceride levels in check. The nondigestible carbohydrates (or fiber) in these foods also help to maintain a healthy gastrointestinal tract by protecting against constipation and intestinal diseases and disorders. Conversely, carbohydrate-rich foods exhibit a far less flattering face when stripped of their protective components and consumed in a refined form.
The World Health Organization (WHO) recommends that 55 to 75 percent of calories come from carbohydrates, although a 2007 scientific update suggested that a lower limit of 50 percent could be acceptable.1,2 WHO adds that not more than 10 percent of calories should come from added sugars. Meanwhile, the Institute of Medicine (IOM) recommends somewhat lower intakes, ranging from 45 to 65 percent of calories from carbohydrates.3 Both organizations agree that whole plant foods, such as vegetables, fruits, whole grains, legumes, nuts, and seeds, should provide most of these carbohydrates.
These health authorities set the lower end of the recommended carbohydrate range (45 to 55 percent of calories) to ensure that people eat enough carbohydrates to meet energy needs. The lower limits also ensure ample intakes of the beneficial compounds associated with carbohydrate-rich foods: fiber, minerals, vitamins, antioxidants, and phytochemicals. When carbohydrate intakes fall below 45 percent of energy, relative fat or protein intakes become excessive, potentially increasing the risk of chronic diseases.
Conversely, not exceeding the higher end of the recommended range (65 to 75 percent of calories) allows for adequate intakes of protein, fat, and their related essential nutrients. For example, intakes below 10 percent of calories from protein may be insufficient for vegans, particularly if the mix of plant foods is limited (for example, with few legumes); if the overall digestibility of the protein is poor (for example, with bulky, very high-fiber diets); or if protein requirements are high (for example, in children and athletes). In addition, fat intakes under 10 percent of calories can be too low to provide sufficient amounts of essential fatty acids, to ensure optimal absorption of fat-soluble nutrients and phytochemicals, or to supply sufficient energy, particularly for infants and children.3
Globally, carbohydrate intakes range from about 40 to 80 percent of calories, with those in developing countries tending toward the higher end of this range; Western dietary patterns fall near the lower end of the range.4 In the United States, carbohydrate consumption averages about 50 percent of calories, which falls within IOM recommendations but below WHO recommendations.3,5 Vegan’s carbohydrate intakes usually are higher, averaging closer to 60 percent of calories.6 Low-fat vegan diets typically provide 75 to 80 percent of calories from carbohydrates; raw vegan and Mediterranean-style diets, which contain generous amounts of nuts, seeds, avocados, and oils, commonly supply closer to 50 percent of calories from carbohydrates.7
Based on the average minimum amount of glucose used by the brain, the recommended dietary allowance (RDA) for carbohydrate is set at 130 grams per day for adults and children. Most adults readily exceed this minimum, with average intakes ranging from 180 to 330 grams per day.3 However, in obesity-ridden nations, advocates of low-carb diets have urged consumers to shun carbohydrates in favor of meat and other protein-rich foods, claiming that carbohydrates are at the root of all health problems. Although there’s no question that diets rich in refined carbohydrates are detrimental to health, there’s strong evidence of the protective effect of carbohydrates from whole plant foods. Long-lived populations throughout the world thrive on diets rich in unrefined carbohydrates.
In contrast, today’s popular low-carb diets provide about 20 to 70 grams of carbohydrate per day—far below the RDA. Two recent systematic literature reviews reported increased all-cause mortality in those who consumed low-carbohydrate diets. The first, from Denmark, reported suggestive evidence for increased all-cause mortality with protein intakes of at least 20 to 23 percent of calories, and suggestive evidence for an inverse relationship between cardiovascular mortality and vegetable protein intake.8 The second, from Japan, reported a 31 percent increase in all-cause mortality in those consuming low-carbohydrate, high-protein diets.9
Finally, a Harvard study that tracked almost 130,000 participants reported that low-carbohydrate diets were associated with a 12 percent increase in all-cause mortality. However, when the researchers separated the participants based on their protein sources, those consuming animal-rich, low-carbohydrate diets had a 23 percent higher all-cause mortality, a 14 percent higher cardiovascular mortality, and a 28 percent higher cancer mortality. In contrast, those consuming plant-rich, low-carbohydrate diets had a 20 percent lower all-cause mortality and a 23 percent lower cardiovascular mortality.10 There’s no question that low-carbohydrate, high-protein diets are effective for weight loss in the short term; however, this benefit becomes irrelevant when weighed against their long-term impact on all-cause mortality.
The term “simple carbohydrates” has long been used to identify potentially harmful carbohydrate sources, while the term “complex carbohydrates” has been used to distinguish the more healthful choices. Not only is this view an oversimplification, it’s fundamentally inaccurate. Whether a carbohydrate is simple or complex is related to its molecular structure, not the healthfulness of the foods in which it’s found.
Simple carbohydrates. Simple carbohydrates contain one or two molecules of sugar. They’re found in whole foods, such as fruits and vegetables, or in refined sweeteners or products made with those sweeteners.
Complex carbohydrates. Starches that contain three or more molecules of sugar are known as complex carbohydrates. They’re found in whole foods, such as whole grains, starchy vegetables, legumes, nuts, and seeds. They can also be found in flours, starches (e.g., cornstarch and potato starch), and products made from these foods.
Unrefined carbohydrates. Carbohydrates naturally present in whole plant foods are unrefined; they may be either simple or complex. Some of the unrefined simple-carbohydrate foods include fruit, dried fruit, and nonstarchy vegetables, such as broccoli, cucumbers, greens, peppers, and tomatoes. Examples of unrefined complex-carbohydrate foods are barley, quinoa, sweet potatoes, and beans.
Refined carbohydrates. Carbohydrate-rich foods made from processed grains (e.g., white flour), other processed starchy foods (e.g., cornstarch), and/or processed sweeteners (e.g., white or brown sugar) are called refined carbohydrates. They may contain either simple or complex carbohydrates. Soda, candy, jam, and jelly are refined simple-carbohydrate foods; bread and pasta made with white flour are refined complex-carbohydrate foods.
Healthful carbohydrates provide an efficient and safe source of energy for the entire body. The only other sources of energy—protein, fat, and alcohol—are less ideal. Protein can be used as a fuel, but it must first be deconstructed by the liver and kidneys to form glucose; if overconsumed, protein is converted to fat for storage. High protein intakes can place a burden on the liver and kidneys, especially in people with existing conditions.
Fat isn’t a preferred energy source either. If the body uses fat instead of carbohydrates for energy on an ongoing basis, by-products called ketones can accumulate. In extreme cases, this can cause ketoacidosis, which drops the body’s pH to dangerously low levels. Finally, in quantities large enough to act as a fuel, alcohol is highly toxic to the body, especially the brain, liver, and pancreas.3,4 That leaves carbohydrates, in all its various forms.
Photosynthesis enables plants to manufacture a variety of carbohydrates, from simple sugars (such as glucose and fructose) to complex carbohydrates (such as cellulose). Plants store energy for later use by stringing together the simple sugars to make the larger carbohydrates called starches (other complex carbohydrates, such as cellulose, are used to create the plants’ cell walls). When young plants sprout and start to grow, they convert stored starches back into simple sugars to support their growth and metabolism. Humans use these carbohydrates in a similar fashion.
Carbohydrates, such as sugars, starches, and fibers, are categorized according to the number of basic sugar molecules (Cn(H2O)n) bound together in larger molecules of various arrangements:
• Monosaccharides. Monosaccharides, such as glucose, fructose, or galactose, are the smallest carbohydrate units and consist of a single molecule of sugar. Monosaccharides aren’t further broken down in the intestinal tract, but rather are absorbed directly into the bloodstream.
• Disaccharides. Two chemically bonded sugar molecules are called disaccharides. The most common disaccharides are sucrose (table sugar), which combines a glucose and a fructose molecule; maltose (malt sugar), which combines two molecules of glucose; and lactose (milk sugar), which links one molecule each of glucose and galactose. Although monosaccharides and disaccharides are both considered simple sugars, the bond between the two component sugar molecules that make up the disaccharides must be broken through enzymatic action before the sugars can be absorbed and used for energy. The related enzymes are sucrase, maltase, and lactase, which break down sucrose, maltose, and lactose, respectively.
• Oligosaccharides. Relatively short carbohydrate chains that comprise three to nine molecules of sugar are called oligosaccharides. Many oligosaccharides are obtained by processing more-complex carbohydrates. For example, malto-dextrin, a maltooligosaccharide used to thicken or bind processed foods, is produced from the breakdown of starch either through enzymatic action and/or acid hydrolysis, or both.
Other types of oligosaccharides aren’t digested before they reach the large intestine; they serve as fuel for beneficial bacteria in the large intestine and may contribute to flatulence. Such oligosaccharides are also known as prebiotics. Examples include ciceritol, fructans (inulin and fructooligosaccharides), raffinose, starchyose, and verbacose. (For helpful tips, see “Dealing with Gas” on page 157.)
• Polysaccharides. Polysaccharides are glucose polymers that consist of at least 10 but often hundreds or thousands of glucose molecules. Polysaccharides are divided into two groups: starch and nonstarch polysaccharides (NSP). The distinction is based on whether the plant uses the polysaccharide for energy storage (starch) or structure (NSP, also known as fiber) and on their digestibility.
Starches are digestible polysaccharides that are broken down by enzymes into glucose molecules. Examples of starches include amylose, amylopectin, and modified starches, such as those used by the food industry as fat replacers or texture enhancers.
NSP are the components of plant cell walls and other indigestible parts of plants that can’t be broken down by enzymes; they make up the bulk of the dietary components known as fiber. When NSP reach the colon, they’re either fermented by colonic bacteria to yield many beneficial compounds and energy, or they’re passed through the stool. Cellulose, hemicelluloses, mucilages, pectin, and plant gums are all examples of NSP found in food.
• Polyols (sugar alcohols). Neither a sugar nor an alcohol, polyols are nonsugar carbohydrates formed by the hydrogenation of either mono- or disaccharides. One part of their chemical structure resembles a sugar molecule and the other part resembles an alcohol molecule. Sugar alcohols are found in small amounts in fruits and vegetables; they’re also manufactured in larger amounts from sugars or starches for use as sweeteners. Although they’re slightly less sweet than sugar, polyols don’t promote tooth cavities. Because they’re poorly digested, they contribute fewer calories per gram than sugars or alcohol. But when consumed in excess, polyols can cause gastrointestinal distress. Examples include erythritol, isomalt, lactitol, maltitol, mannitol, polydextrose, sorbitol, xylitol, and hydrogenated starch hydrolysates.3,4,11,12
Carbohydrates supply approximately 4 calories per gram, as does protein. (In practical terms, 1 tablespoon of either pure protein or carbohydrate provides about 50 calories.) When nutritional analyses are performed, all carbohydrates are calculated as providing 4 calories per gram, regardless of the degree to which they are digested.
The relative digestibility of plant carbohydrates depends on the plants’ growth stage when consumed; the riper the plant, the more digestible its carbohydrates. As plants ripen, they convert their stored carbohydrates into the simpler sugars that sweeten fruits and vegetables. Then, when food preparation begins and the plants’ cells are broken down by chopping, grating, blending, juicing, and cooking, starch-digesting enzymes in the plants are activated.
Once carbohydrates enter the mouth, amylase (a starch-splitting enzyme in saliva) begins to sever some of the bonds between the molecules in the starches. However, the greater part of starch digestion occurs in the small intestine, where additional enzymes break down the starches to allow monosaccharides to pass through intestinal walls and enter the blood.
Once in the bloodstream, glucose is either used for energy or removed by the liver and converted into a storage carbohydrate called glycogen. The body can store only limited amounts of glycogen, so excess glucose is converted into fatty acids for unlimited long-term storage as fat. Meanwhile, fructose and galactose are quickly taken up by the liver and converted to glucose to be used for immediate energy. If there’s already enough energy available, they too are converted to glycogen for short-term storage or fatty acids for long-term storage.
Fiber and nondigestible oligosaccharides aren’t broken down in the small intestine but move on to the large intestine, where they either add bulk to the stool or are used as food by intestinal bacteria. Consequently, the usable calories in many high-fiber, high-carbohydrate foods may be overestimated. In other words, high-fiber foods may actually provide somewhat fewer calories than the amounts listed in nutrient databases. Some experts suggest that for carbohydrates that reach the large intestine intact (i.e., fiber), the calorie count should be 2 calories per gram.4
Fiber does provide some calories. When it reaches the large intestine, short-chain fatty acids are produced as a by-product of microbial fermentation; these fatty acids are absorbed into the blood stream, providing some energy in the process.11
Besides serving as a major source of calories, unrefined carbohydrate-rich whole plant foods can help to reduce hunger, control blood glucose and insulin metabolism, and keep cholesterol and triglyceride levels in check. These foods also help to maintain a healthy gastrointestinal tract by protecting against constipation and intestinal diseases and disorders. Most of these beneficial effects are the result of the nondigestible content of carbohydrates, better known as fiber.
Fiber has come to be viewed as nature’s broom—the part of plants that keeps things moving smoothly and efficiently through the body’s intestinal tract. Its benefits became universally recognized in the 1970s when researcher Denis Burkitt discovered that rural Africans were free of Western diseases, such as heart disease, diabetes, and obesity, as well as intestinal disorders, such as colon cancer and constipation. He determined that dietary fiber set Africans apart from Westerners and that size and frequency of bowel movements were excellent predictors of health.
Burkitt’s message was enthusiastically embraced by the public. Wheat bran became the food fad of the decade and was added to everything from muffins to meat loaf. What consumers failed to realize was that spiking their diet with wheat bran didn’t provide the same benefits as consuming a variety of high-fiber plant foods, as rural Africans do or as Burkitt advocated.
Although technical differences exist throughout the world, most definitions of fiber include all nonstarch polysaccharides (NSP) with 10 or more sugar molecules, oligosaccharides (3 to 9 molecules), and lignin (a noncarbohydrate component of plant cell walls).3,11,15 Dietary fiber can’t be broken down by digestive enzymes in the small intestine of humans.
Another type of fiber—called functional, novel, or added fiber—consists of non-digestible carbohydrates that are extracted from plants or synthetically produced, and that have some health benefits. Most functional fibers are oligosaccharides (isolated from plants or synthetically produced) or manufactured NSP.
The IOM defines total fiber as “the sum of dietary fiber and functional fiber.” The inclusion of functional fiber in this definition is controversial within the international scientific community, because there’s concern that functional fiber may not provide the same physiological benefits as dietary fiber. For example, a manufacturer could add isolated or synthetic fiber to otherwise unhealthy food, declare its high fiber content, and mislead consumers into thinking that the food is nutritious. By contrast, whole plant foods are naturally good sources of fiber, are rich in dozens of nutrients and phytochemicals, and are beneficial to health in myriad ways.11
Fiber has traditionally been divided into two categories: soluble and insoluble. Examples of soluble fibers are gums, mucilages, and pectins. Cellulose and lignin are examples of insoluble fiber. Hemicelluloses and beta-glucans vary in solubility, although hemicelluloses are usually insoluble and beta-glucans are usually soluble. All fiber-rich foods contain both soluble and insoluble fibers.11,16
For many years, experts believed a fiber’s solubility determined its physiological effects. It was thought that soluble fiber formed viscous gels and was fermentable, thus favorably impacting blood glucose and blood cholesterol. Insoluble fiber was associated with stool bulk and regularity.
However, more recent research suggests that the physiological benefits attributed to soluble and insoluble fiber are highly inconsistent. For example, some types of soluble fiber have little influence on blood glucose or cholesterol but do improve gut health and regularity. Likewise, some insoluble fiber is rapidly and completely fermented in the large intestine, and therefore wouldn’t contribute to stool bulk as expected.
The research concludes solubility doesn’t predict viscosity or fermentability. Many of the earlier studies were done using isolated fibers, rather than the plant foods in which these fibers coexist. So while the terms “soluble” and “insoluble” are useful when referring to specific, isolated types of fiber, they’re less useful in relation to whole foods. Although these terms have long been used to classify fiber types in research papers, in nutrition education materials, and on food labels, scientific health authorities are attempting to phase them out and use viscosity and fermentability instead.16
• Viscous and nonviscous fiber. Viscous fiber becomes gel-like or thick and gummy when mixed with water. Nonviscous fiber may absorb water but doesn’t become gluey. While fiber must be somewhat soluble to make water viscous or gel-like, not all soluble fiber has this property. Viscosity is thought to be responsible for some of fiber’s greatest health advantages. Viscous fiber helps to delay stomach emptying and increases feelings of fullness after eating. It can stabilize blood glucose levels and reduce blood cholesterol. Guar gum, mucilages, and pectin are all examples of viscous fiber. Cellulose and lignin are examples of nonviscous fiber. Hemicelluloses and beta-glucans can fall into either category, although most hemicelluloses are nonviscous and most betaglucans are highly viscous. 17
• More-fermentable and less-fermentable fiber. Fiber feeds bacteria in the colon. These microorganisms extract energy from fiber by fermenting it, creating short-chain fatty acids and intestinal gases as by-products. The short-chain fatty acids can be absorbed into the bloodstream and used by the body for energy. Butyrate, a major short-chain fatty acid metabolite, is the preferred energy source for colonocytes (cells lining the colon); some evidence exists that a lack of butyrate may contribute to ulcerative colitis and colon cancer.3
The types of fiber most fermentable by bacteria include beta-glucans, guar gum, hemicelluloses, pectins, and nondigestible oligosaccharides. Gums and mucilages are the most slowly fermented, while oligosaccharides are the most rapidly fermented. Less-fermentable types of fiber, such as cellulose, resistant starch, and lignin, make an impressive contribution to stool bulk. Wheat bran is an excellent example of a food rich in these less-fermentable fibers. For various types of fiber and their food sources, see table 5.1.
While the benefits of fiber begin in the intestine, they extend to every part of the body. High-fiber diets positively contribute to gastrointestinal health, cardiovascular health, blood glucose control, and weight management:
• Gastrointestinal health. Fiber is important for preventing constipation, diverticulosis (small sacs in the wall of the intestines that press outward), and hemorrhoids (painful, swollen tissues in the anus and rectum). It may also protect against intestinal cancers (especially colorectal cancers), gallstones, and inflammatory bowel diseases, such as ulcerative colitis. A high-fiber diet makes stools softer and heavier, helping them pass more easily and rapidly out of the colon. While the insoluble, nonviscous, less-fermentable fibers, such as cellulose and lignin, are particularly helpful in this regard, fiber fermented in the colon also contributes to stool softening and bulk. It’s estimated that for every 3.5 ounces (100 g) of carbohydrate fermented in the colon, about 1 ounce (30 g) of bacteria is produced, contributing to fecal mass.3,11
TABLE 5.1. Common sources of specific fibers
TYPE OF FIBER |
COMMON SOURCES |
Beta-glucans |
Oats, barley, and mushrooms |
Celluloses* |
Grains, fruits, vegetables, legumes, nuts, and seeds |
Gums and mucilages (used to thicken, stabilize, and add texture to foods) |
Seeds, such as psyllium and guar seeds (guar gum), and sea vegetable extracts, such as carageenans and alginates |
Hemicelluloses** |
Fruits, grains (especially outer husks), legumes, nuts, seeds, and vegetables |
Lignins |
Stringy vegetables and the outer layer of cereal grains |
Nondigestible oligosaccharides |
Fruits, grains, legumes, and vegetables |
Pectins |
Berries and fruits (especially apples and citrus fruits) |
Resistant starches |
Legumes, raw potatoes, underripe bananas |
*Celluloses account for about 25 percent of the fiber in grains and fruits and 33 percent in vegetables and nuts.
**Hemicelluloses account for about 33 percent of the fiber in plants.
Many fermentable carbohydrates serve as prebiotics, stimulating the growth of friendly bacteria in the colon. These beneficial bacteria and the fermentation products they generate (carbon dioxide, hydrogen, methane, and short-chain fatty acids) reduce the pH of the colon and feces, inhibiting the growth of harmful yeast and bacteria. Friendly bacteria can also enhance mineral absorption, reduce food sensitivities and allergies, disable carcinogens, attack cancer cells, and favorably affect the metabolism of fat and sugar.3,11
• Cardiovascular health. In numerous studies, fiber-rich diets have been associated with a reduced risk of cardiovascular disease.19 One pooled analysis of ten prospective cohort studies reported that each additional 10 grams of dietary fiber was associated with a 14 percent decrease in risk of coronary events and a 27 percent decrease in coronary death.19 (See table 5.2 on page 160 for the fiber content of common foods.) Another study of more than 40,000 male health professionals reported that participants who consumed the greatest amounts of fiber had a 40 percent reduction in the risk of developing coronary artery disease, compared to those consuming the smallest amount of fiber.20
It’s difficult to determine whether these benefits are attributable only to fiber, to other healthful components in plant foods, or to reductions in saturated fat, trans-fatty acids, and cholesterol associated with plant-based diets. However, research suggests a variety of mechanisms by which fiber may exert protection. One popular theory is that soluble, viscous fiber binds with bile acids that contain cholesterol, carrying them out with the feces.19 Other possibilities include reduced synthesis of fatty acids by the liver (because products of fermentation inhibit their production) and increased satiety leading to reduced caloric intake.21 Fiber can also reduce blood pressure, improve enzymatic breakdown of fibrin that can help to remove blood clots, and enhance insulin sensitivity.19
• Diabetes and metabolic syndrome. Fiber intake has been associated with a reduced risk of metabolic syndrome and type 2 diabetes.22–25 Fiber, particularly soluble viscous fiber, delays the absorption of fat and carbohydrates from the small intestine, favorably influencing insulin levels and blood glucose response. Delayed absorption of carbohydrate and fat helps to curb appetite, possibly reducing overeating and weight gain.11
• Overweight and obesity. High-fiber foods are associated with reduced overweight and obesity. Generally, high-fiber foods take more space on plates and in stomachs; they also require more chewing. Many high-fiber foods are less energy dense, meaning they have fewer calories for a specific volume of food. All these factors contribute to satiety or feelings of fullness.11
Populations that consume very high-fiber diets generally have low rates of chronic disease. As a result, WHO recommends at least 25 grams of dietary fiber per day for adults;1 IOM recommends 14 grams of fiber per 1,000 calories for everyone older than 1 year.3 Although an RDA hasn’t been set for fiber, the Adequate Intake (AI) was established in accordance with this 14-gram figure. Based on average energy intakes for various ages and genders, the daily AI is 38 grams for men 19 to 50 years old (30 grams for older men), and 25 grams for women 19 to 50 years old (21 grams for older women). The International Life Sciences Institute suggests that an intake of 32 to 45 grams of fiber per day may be necessary to achieve the critical fecal mass of 160 to 200 grams per day (about 5.5 to 7 ounces) necessary for preventing constipation.11
Nutritional anthropologists estimate preagricultural fiber intakes at 70 to 150 grams per day.26 Clearly, cavemen ate a lot of plant foods (for more on this topic, see pages 279 to 281). In contrast, Western-style diets provide about half the current recommended intakes, or approximately 15 to 17 grams of fiber per day.27,28 Among contemporary populations, high fiber intakes have been reported in rural Chinese (up to 77 grams of fiber per day) and rural Africans (60 to 120 grams of fiber per day).26 Average vegan intakes consistently exceed the AI. Based on studies conducted between 1984 and 2005, vegan men average 45 to 50 grams of fiber per day and vegan women average 35 to 40 grams of fiber per day.6
Vegans are at a definite advantage when it comes to stool bulk and healthy laxation, and are the one dietary group in the Western world that typically exceeds current recommended fiber intakes. Switching to a vegan diet normally solves any problems with irregularity, but additional steps also may be taken:
• Eat at least one serving of legumes (½ to 1 cup/125 to 250 ml) per day. Add beans to soups, stews, loaves, and patties; top salads with them. Note that processed alternatives, such as tofu and vegan meat substitutes, are much lower in fiber.
• Aim for nine or more servings of vegetables and fruits each day. Wash but don’t peel fruits and vegetables. Eat a good proportion of these foods raw. Enjoy a large raw salad every day. When cooking vegetables, minimize cooking time. Select higher-fiber options more often. (See table 5.2 on page 160.)
• Opt for intact whole grains most of the time. Grinding breaks down fiber, and smaller particles generally contribute less to stool bulk. While bran increases stool bulk greatly, it’s best to rely on whole grains rather than isolated bran due to the latter’s negative impact on mineral absorption.
• Sprinkle on seeds. Seeds can increase stool weight. Whole flaxseeds are especially effective, as are psyllium seeds, though even ground seeds are helpful.
The menus on pages 439 to 442 provide between 48 and 88 grams of fiber. In addition, for excellent recipes that list fiber content and include a complete nutritional analysis, see Cooking Vegan by Vesanto Melina and Joseph Forest (Book Publishing Company, 2012) and Becoming Raw by Brenda Davis and Vesanto Melina (Book Publishing Company, 2011).
• Select whole-grain options when using processed grain products. Read labels. Aim for at least 2.5 grams of fiber in a serving of bread or pasta and 5 grams from a serving of breakfast cereal.
• Spike baked goods with high-fiber ingredients. Use or buy cookies, muffins, breads, or other baked goods that contain high-fiber ingredients. When baking from scratch, use dates, prunes, or bananas in place of sugar; nut or seed butters or applesauce in place of oil; coarsely ground whole-grain or sprouted-grain flours in place of refined flour; and ground flaxseeds in place of eggs.
• Choose high-fiber snacks. Raw fruits and vegetables, trail mixes, stuffed dates or other raw treats, and popcorn are excellent options.
• Keep well hydrated. Most people need at least 8 cups (2 L) of fluid each day.
• Exercise daily. Whether it’s a brisk walk or jog, an aerobics or yoga class, a swim or game of tennis—any physical activity keeps intestines working well.
On average, people pass gas twelve to twenty-five times a day. Gas production protects the colon against genetic damage that may lead to cancer; it dilutes carcinogens, stimulates beneficial bacterial growth, favorably alters the gut pH, and improves the function of the epithelial cells of the colon.11,29 Of course, there’s a point at which passing gas becomes a social liability. The annoyance and embarrassment caused by flatulence provides grounds for some people to drastically limit or even avoid beans and high-fiber foods altogether.
However, a recent study found that only about 50 percent of participants who added ½ cup (125 ml) of pinto beans, black-eyed peas, or vegetarian baked beans to their daily diet experienced an increase in flatulence during the first week of their addition compared to those who added ½ cup (125 ml) of carrots. Of the participants who experienced increased flatulence with bean intake, 70 percent found that it dissipated by the second or third week of daily bean consumption.30
There are two main causes of gas: swallowing air and bacterial fermentation of carbohydrates that reach the large intestine. The following suggestions will help to keep gas production tolerable.
To reduce the amount of air swallowed:
• eat slowly and with the mouth closed
• chew food well
• avoid drinking carbonated beverages, chewing gum, and sucking on candies
• make sure dentures fit properly
To diminish the impact of undigested carbohydrates that reach the colon:
• Reduce the oligosaccharides in beans. Beans are among the most notorious flatulence producers. The offending compounds are raffinose, starchyose, and verbacose—oligosaccharides that can’t be broken down before they reach the colon because humans don’t produce alpha-galactosidase, the enzyme needed to break apart the bonds in the oligosaccharides found in beans. They arrive in the colon relatively undigested and are fermented by bacteria in the colon, resulting in intestinal gas. There are a number of ways to reduce oligosaccharide intake from beans:
1. Use fresh beans instead of dried beans because their oligosaccharide content is much lower.
2. Buy only as many dried beans as can be used within a few months. The longer beans are stored, the higher their oligosaccharide content becomes.
3. Soak beans for about twelve hours or overnight; discard the soaking water and rinse well before placing in fresh water and cooking. Plan ahead for a double soak, during which this procedure is completed twice before cooking. If there’s no time to soak, boil the beans briefly, let them sit in the water for an hour or two, discard the soaking water, rinse well, and cook in fresh water. When boiling beans, remove any white foam that forms at the surface; this foam contains oligosaccharides.
4. Sprout legumes. Sprouting converts oligosaccharides into sugars.31 Sprouted mung beans, lentils, and peas can be eaten raw. Other legumes should be cooked after sprouting. Soak beans for twelve to twenty-four hours, drain, and rinse well; then sprout for at least one to three days, or until small sprouts appear. Be sure to rinse and drain two or three times a day. Once the beans have a tiny sprout, they’re ready to cook; sprouting cuts cooking time in half.
5. Start with small portions of beans and gradually increase the portion size. This will allow time for more formation of bacterial flora that can completely digest oligosaccharides.
6. Make sure beans are thoroughly cooked. Undercooked beans are more difficult to digest. Beans are sufficiently cooked when they can easily be crushed between the tongue and the roof of the mouth.
7. Rinse canned beans well before eating.
8. Select small legumes that are easier to digest. The least problematic are skinless, split legumes, such as mung dahl (split mung beans), red lentils, and split peas. Generally, smaller beans, such as adzuki and mung beans, are easier to digest than large beans, such as lima or kidney beans.
9. Include fermented bean products, such as tempeh and miso, and lower-fiber legume options, such as tofu.
In South America, Africa, China, the Middle East, and India, legumes have served as dietary staples for centuries. Per capita consumption of legumes is approximately 6.5 pounds (about 3 kg) per year in the United States;33 intakes exceeding 88 pounds (40 kg) per year are common in countries that rely on legumes as dietary staples, and intakes of up to 145 lbs (66 kg) per year have been reported in some African countries (e.g., Kenya).34
Legumes provide many of the key nutrients found in meat (e.g., protein, iron, and zinc) along with protective compounds concentrated in plants and largely absent from meat (fiber, plant sterols, antioxidants, and phytochemicals). Recent evidence suggests that the nonheme ferritin iron in legumes is highly absorbable and may provide important advantages over heme iron or iron supplements.35 (For more on iron, see pages 186 to 189.)
Researchers at the US Department of Agriculture Food Composition and Nutrient Data Laboratories assessed the total antioxidant capacity of more than one hundred foods and released a rather stunning result—legumes claimed three of the top five prizes. Another study reported that legumes were the only food group found to produce a significant reduction in mortality. For every 0.66-ounce (20 g) increase in daily bean intake, risk of death dropped 7 to 8 percent.36 Legume consumption has also been shown to favorably alter the risk of developing cancer, cardiovascular disease, and diabetes and to provide benefits in weight loss.37
Although dried beans contain lectins (often associated with food allergies) and phytate (substances that reduce mineral absorption), common food preparation methods significantly reduce or eliminate these compounds, particularly lectins.
• Use seasonings that counteract the production of intestinal gas. Spices prized for their ability to ward off gas production are cloves, cinnamon, garlic, turmeric, black pepper, asafetida (hing), and ginger.32 The Mexican spice epazote and the Japanese seaweed kombu are commonly added to foods to neutralize the gas-producing compounds they contain.
• Improve gut flora. Take probiotics in supplement form or use in preparing fermented vegan cheeses, yogurts, and other dishes.
• Avoid overeating. Eat smaller meals; stop eating when 80 percent full.
• Limit foods rich in added fructose or sugar alcohols. The small intestine isn’t equipped to handle large quantities of fructose or sugar alcohols, such as sorbitol, maltitol and xylitol; when these sugars aren’t completely absorbed, they’re fermented by bacteria in the colon. Even fructose from fresh or dried fruits can be a problem when consumed in excess.
• Take activated charcoal. Taking activated charcoal right before eating foods that trigger flatulence is reported to reduce both the amount and odor of intestinal gas.
• Take an enzyme supplement with gas-producing food. If all else fails, consider taking a supplement containing the oligosaccharide-digesting enzyme alpha-galactosidase, which humans do not produce.
All whole plant foods provide fiber; it’s what gives plants their structure. (Animal products don’t contain fiber; bones give animals structure.) Table 5.2 provides a list of the fiber content of foods.
TABLE 5.2. Fiber content of selected whole plant foods
AMOUNT OF FIBER PER CUP OR SERVING |
FOOD AND SERVING SIZE |
Very high-fiber foods 10 to 19.9 g |
Legumes (all varieties), cooked, 1 c (250 ml) Split peas, cooked, 1 c (250 ml) Avocado, medium, 6.7 oz (200 g) High-fiber bran cereals, ½ c (125 ml) |
High-fiber foods 5 to 9.9 g |
Berries (raspberries, blackberries), fresh, 1 c (250 ml) Fruit (Asian pears, papayas, pears), medium Dried fruit (apricots, figs, peaches, pears, prunes, raisins), ½ c (125 ml) Coconut, fresh, shredded, ½ c (125 ml) Flaxseeds, 2 T (30 ml) Grains (most whole grains), cooked, 1 c (250 ml) Potato, regular or sweet, baked, medium Pasta, whole wheat, 1 c (250 ml) Artichoke, medium |
Moderate-fiber foods 2 to 4.9 g |
Berries (blueberries, strawberries), fresh, 1 c (250 ml) Fruit (most varieties), 1 medium/2 small or 1 c (250 ml) Vegetables (most), raw: 2 c (500 ml); cooked: 1 c (250 ml) Nuts and seeds (most varieties), ¼ c (60 ml) Grains (brown rice, millet, oats), cooked, 1 c (250 ml) Whole-grain breads (read label), 2 slices Pasta, white, 1 c (250 ml) Popcorn, 3 c (750 ml) |
Lower-fiber foods 1.9 g or less |
Melon, 1 c (250 ml) Fruit or vegetable juice (all varieties), 1 c (250 ml) Sprouts* (grain, legume, or vegetable), 1 c (250 ml) Lettuce, all types, 2 c (500 ml) Cucumber, medium, 8 in (20 cm) Refined grains, most (white rice, Cream of Wheat), ½ c (125 ml) Refined cold cereals, 1 oz (30 g) |
Source:13
*The fiber content in sprouts is far lower than the fiber in an equal volume of the unsprouted food, because it takes only a few tablespoons of the unsprouted food to produce a cup of sprouts (which are largely water). Furthermore, some of the fiber in seeds or legumes is converted to simple sugars during the sprouting process.
Though possible, excessive fiber intake is unlikely if consumers eat whole plant foods and drink sufficient fluids. Excessive fiber is more of an issue for people who consume concentrated fiber sources, such as wheat bran, in large amounts. In small children, very high fiber intakes can make the diet too bulky, jeopardizing energy intake and potentially resulting in failure to thrive. This is seldom a concern in healthy adults.
Fiber can bind calcium, iron, and zinc and reduce their absorption, although these minerals are at least partly liberated during fermentation in the large bowel. Short-chain fatty acids (also products of fermentation) help to facilitate their absorption from the large bowel.11 In addition, compared to refined foods, high-fiber whole foods generally provide enough extra minerals to compensate for any losses incurred. In contrast, concentrated fiber such as wheat bran, which is particularly high in phytate, can inhibit mineral absorption when routinely added to other foods. It’s best to limit the use of wheat bran and avoid fiber supplements in fiber-rich plant-based diets. (For more on phytates, see page 181.)
Carbohydrate Content of Whole Foods
In plant foods, the percentage of calories from carbohydrates ranges from about 90 percent in fruits and starchy vegetables to about 12 percent in nuts and seeds. (See table 3.5 on page 97 and figure 5.1 for more-precise percentages of calories from carbohydrates in common foods. These figures are based on current nutrient analysis methodology; all carbohydrates are calculated as 4 calories per gram, regardless of fiber content.)
FIGURE 5.1. Average percentage of calories from carbohydrates in common foods
Source:13
While most carbohydrates are derived from plant foods, relatively few are consumed as whole foods. Instead, nutritious plants are routinely transformed into fat-, sugar-, and salt-laden processed foods whose lure is undeniable.
When whole plant foods are processed or refined, many of their nutritious elements are destroyed or discarded. For example, the process of turning wheat berries into white flour causes the loss of approximately 80 percent of their vitamins, minerals, and fiber. In addition, a 200- to 300-fold loss in phytochemicals occurs.14 When whole wheat grains are milled into white flour, the grains’ bran and germ are removed, leaving behind only the endosperm. Bran, the outer husk of the grain, protects its contents. (Although bran provides nutrients and phytochemicals, its main claim to fame is fiber.) To support the life and growth of a new wheat plant, a grain’s germ contains essential fatty acids, vitamins, minerals, and phytochemicals. The remainder of the grain, its endosperm, comprises mainly starch, some protein, and a miniscule amount of vitamins and minerals. The end-product—white flour—may have a long shelf life, but it has little remaining nutritional value with which to support human or other life.
The metabolic processes that transform starches and sugars into useable energy require many of the nutrients lost in refining. To compensate, food processors add back some of these nutrients. For example, after wheat is refined, it’s commonly enriched with thiamin, riboflavin, niacin, folic acid, and iron. However, other vitamins and minerals lost during processing—vitamin B6, vitamin E, pantothenic acid, zinc, boron, selenium, magnesium, potassium, and manganese—are not added back, nor are any of the fiber or phytochemicals.
Few health experts would dispute that processed or refined carbohydrates can be damaging to health. Promoters of low-carb diets (e.g., Atkins, Protein Power, The Zone, South Beach, primal, and paleo diets) go one step further, claiming that carbohydrates are responsible for rising rates of obesity and chronic disease, regardless of their origin.
However, anticarbohydrate gurus overlook the fact that many of the healthiest populations in the world consume high-carbohydrate diets—and that many of those carbohydrates come from unrefined sources and whole foods. Unrefined carbohydrates are consistently associated with the reduction of disease risk. What really matters is whether or not the carbohydrate is consumed in, or close to, its natural whole state—as it was grown. When the sources of carbohydrates are vegetables, fruits, legumes, whole grains, nuts, and seeds, also present are vitamins, minerals, antioxidants, phytochemicals, fiber, and essential fatty acids.
Humans were born with a soft spot for sweets, and for good reason. In nature, sweetness generally signals safety, while bitterness serves as a warning flag. The simple sugars in plants also provide a reasonable concentration of glucose to keep the human machine running smoothly. Normally, it’s difficult to consume excessive sugar when eating a variety of vegetables, fruits, legumes, grains, nuts, and seeds.
Yet when sugars are extracted from whole foods and used to augment baked goods, beverages, and other sweet offerings, their increased availability exploits the human bias for sugar. The passion for sweet foods has steadily increased. In the United Kingdom, sugar consumption averaged 4 pounds in 1700 and 18 pounds in 1800.38 By 1900, per capita added-sugar intakes in the United States were estimated at 64 pounds per year, which ranked among the highest in the world.39 Between 1900 and 2005, this figure jumped to 142 pounds per person per year.
After factoring in losses (what goes down sinks and into the garbage), actual sugar intakes in the United States are estimated at 30 teaspoons of sugar per person per day—about 480 calories, or almost 25 percent of calories in a 2,000-calorie diet.40 Soft drinks and other sugar-sweetened beverages account for close to half the added sugars consumed by Americans. Between 1970 and 2000, the consumption of sugary soft drinks increased by 70 percent, from 7.8 ounces to 13.4 ounces per person per day.38
Between 1970 and 1995, sugar intake increased by 19 percent. However, the most notable change wasn’t the amount of sugar consumed, but the type. While consumption of sucrose (table sugar from cane and beet sugars) declined by 38 percent, the intake of corn sweeteners (mainly high-fructose corn syrup) increased by 387 percent.40 By 2007, 45 percent of total added sugars came from sucrose, 41 percent came from high-fructose corn syrup (HFCS), and 14 percent came from glucose syrup, pure glucose, and honey.41
Sugar itself, whether a monosaccharide (such as fructose) or disaccharide (such as sucrose), isn’t inherently harmful. Simple sugars aren’t poison—they’re molecules that the human body prefers as a fuel source and can handle fairly well in reasonable doses. In fact, when it’s part of a whole plant food, sugar is a valuable and healthful source of energy. Even adding small amounts of additional sugars to nutritious prepared foods doesn’t appear to pose a health risk. It’s excess sugar consumption that’s the issue, particularly when it comes from refined sweeteners.
The detrimental effects of eating sugar are most pronounced with excess calorie consumption. Diets that obtain a high proportion of calories from added sugars (and, in most instances, other refined carbohydrates) are associated with adverse health consequences:
• Reduced micronutrient intakes. More-nutrient-dense foods may be crowded out.
• Hypertension. Excessive sugar intake may raise blood pressure.38,42
• Elevated triglycerides. Sugar increases triglyceride levels, with fructose having the most significant impact. The effect appears to be even greater in men, in sedentary and overweight individuals, and in those with metabolic syndrome.2,3,38,41–43
• Decreased HDL cholesterol. Fructose appears more potent than sucrose in reducing HDL cholesterol levels.3
• Increased insulin secretion and insulin resistance. Sugars increase blood sugar levels and insulin secretion; fructose is also associated with increased levels of visceral fat (fat in and around vital organs), further increasing insulin resistance.41
• Increased cancer risk. Limited evidence suggests that high intakes of sucrose increase the risk of colorectal cancer,2,44–46 and high intakes of lactose raise the risk of ovarian cancer.2,44 There’s also limited evidence that high intakes of sugar increase insulin-like growth factor 1 (IGF-1), and that elevated IGF-1 boosts the risk for breast cancer.47,48
• Overconsumption. Added sugars, especially from beverages, can result in excessively high total energy consumption, contributing to overweight and obesity.2,3,49
• Poor dental health. High sugar intakes are strongly associated with dental caries and reduced dental health.3
• Nonalcoholic liver disease (NAFLD). About 70 percent of people with metabolic syndrome are also afflicted with NAFLD. Excessive intake of simple sugars, particularly fructose in soft drinks, is thought to cause accumulation of fatty acids in the liver. People with NAFLD are at increased risk for atherosclerosis (plaque-filled arteries) and cardiovascular disease.43
• Inflammation. Proinflammatory molecules may increase with elevated blood glucose levels, especially in insulin-sensitive individuals.50–53
• Impaired immunity. Short- and long-term elevations in blood glucose may adversely affect immunity and increase susceptibility to infection, although research is very limited.50–52,54
• Increased formation of advanced glycation end-products (AGE). Limited research suggests that fructose is linked to AGE formation within body cells and is approximately eight times more likely to form these compounds than glucose. AGE contribute to numerous disease processes and accelerate aging.55
Where sugar is concerned, it’s the dose that makes the poison. The USDA Dietary Guidelines for Americans recommend that no more than 5 to 15 percent of calories come from added sugar and solid fat. While the guidelines don’t specify a percentage for either, assuming equal amounts would mean allowing no more than 150 calories from sugar in a 2,000-calorie diet, or about 9 teaspoons (45 ml) of sugar per day.56 The American Heart Association has more specific guidelines for added sugar—no more than 6 teaspoons (30 ml) per day for women and 9 teaspoons (45 ml) per day for men.
The big challenge in trying to follow these guidelines is determining the amount of sugar in processed foods. Food labels provide a clue. On the Nutrition Facts panel, manufacturers must list the total amount of sugar in grams per serving (including sugars naturally present in foods plus any added sugar). There are approximately 4 grams of sugar in 1 teaspoon (5 ml), so 32 grams of sugar would equal roughly 8 teaspoons (40 ml). The serving size also matters; servings are often smaller than consumers expect.
In addition, food manufacturers aren’t required to separately note added sugars, except in the ingredient listing. If the food had no natural sugars, then any sugar listed is all added sugar. (The exception to this rule is fruit juice concentrate, which is included as an added sugar.) If the food contains natural sugars from fruits, dried fruits, or even vegetables, such as tomatoes, the ingredient list needs further scrutiny. If sugar (sucrose or high-fructose corn syrup) is high on the list, the amount of added sugars likely is also high.
Some manufacturers try to push sugars lower down on the ingredient list by using several different sweeteners, some of which consumers might not recognize as sugar. These include:
• agave nectar
• barley malt syrup
• blackstrap molasses
• brown rice syrup
• brown sugar
• cane sugar
• corn syrup
• crystalline fructose
• dextrose
• dried cane juice
• evaporated cane juice
• fructose
• fruit juice concentrate
• glucose
• high-fructose corn syrup
• honey
• invert sugar
• lactose
• malt syrup
• maltodextrin
• maltose
• maple syrup
• molasses
• raw sugar
• rice syrup
• Sucanat
• sucrose
• syrup
• turbinado sugar
In 2008, more than 20 billion gallons of soft drinks were sold in America.57 That amounts to approximately two 12-ounce (180 ml) soft drinks per day for every man, woman, and child in the nation. Soft drinks include all beverages with added sugars: nondiet sodas, fruit drinks, energy drinks, sports drinks, lemonade, sweet powdered drinks, vitamin waters, and sweetened iced teas.
The average 12-ounce (180 ml) serving of soda or fruit drink provides about 150 calories from sugar; some sweetened beverages have even more. That’s close to 10 teaspoons (50 ml) of sugar per serving. One 12-ounce (180 ml) serving, added to the daily diet, can cause a weight gain of about 15 pounds (6.8 kg) per year. While consumers might believe they can compensate for those calories by reducing intake elsewhere, the evidence suggests otherwise. When calories arrive in liquid form, the body fails to register those calories with the appetite-control center quite as precisely as it does solid food. If those calories aren’t consciously offset, weight gain will result.
In fact, scientific studies consistently link consumption of soft drinks with weight gain.58,59 A high intake of soft drinks has also been linked with osteoporosis and dental cavities.60 Researchers also recently reported a surprising association between soda consumption and lung diseases, such as chronic obstructive pulmonary disorder and asthma.61
The basic message is simple: both adults and children should avoid sugar-sweetened beverages. Beverages that are naturally calorie-free, such as water, soda water (with a squeeze of lemon or lime), or herbal tea are best. Other healthful options are fresh-squeezed vegetable and fruit juices. (Fruit juices are higher in calories and natural sugars, so should be limited; when mixed with carbonated water, they’re a great stand-in for sweet soda.)
Sweeteners fall in and out of favor with health-conscious consumers on a regular basis, but the differences between various simple sugars are of relatively minor consequence. Most sugars are essentially glucose, fructose, or some combination of the two.
Some people select sweeteners based on their effect on blood glucose levels or their glycemic index. (For more on the glycemic index, see pages 172 to 178.) Pure glucose raises blood glucose levels quite quickly; pure fructose doesn’t. However, consuming more fructose isn’t an advantage because it appears to be more damaging than glucose when consumed in excess.
Although a few sweeteners contain tiny amounts of nutrients, most make no significant contribution to nutritional needs when consumed in normal quantities. One notable exception is blackstrap molasses; 2 tablespoons (30 ml) can provide as much as 400 mg of calcium, 7 mg of iron, 1,200 mg of potassium, and 200 mg of magnesium (check labels).13 That’s more calcium than 1 cup (250 ml) of milk, more iron than an 8-ounce (240 g) steak, more potassium than two large bananas, and more magnesium than 1 cup (250 ml) of quinoa. (Choose organic molasses to avoid pesticides.)
Date sugar is made from dried and ground dates, so it’s a whole-food sweetener and is more nutrient dense than most other sugars. However, it’s expensive and not widely available. Other minimally refined sugars, such as maple syrup and coconut palm sugar (derived from the sap of the coconut palm tree), are slightly more nutrient dense than heavily refined products.
While intake of sugars should be minimized, judicious use is acceptable. The top vegan choice would be a sweetener that’s organic, fair trade, and minimally refined. The most nutrient dense—and often the most economical—sweets are whole foods, including fruits and dried fruits, such as dates. Both are commonly used as a primary sweetener in creative vegan and raw vegan recipes.
Sweeteners fall into two categories: nutritive or caloric sweeteners and nonnutritive or noncaloric sweeteners. Simple sugars, such as fructose and sucrose, are nutritive sweeteners. So are sugar alcohols.
Consumers often confuse sugar alcohols with noncaloric sweeteners and assume they’re calorie-free. Although poorly digested, they do provide an average of about half the calories of other carbohydrates, or about 2 calories per gram. Common sugar alcohols include erythritol, isomalt, lactitol, maltitol, mannitol, sorbitol, polydextrose, xylitol, and hydrogenated starch hydrolysates.
Although sugar alcohols affect blood glucose, their impact is less than that of other carbohydrates.64,65 This quality makes them attractive to food manufacturers. Products that contain sugar alcohols are often labeled “sugar-free”; however, most experts recommend including half the grams of sugar alcohol in a total-carbohydrate count.
As an added bonus, sugar alcohols aren’t as likely as simple sugars to attract molds or bacteria, making them very shelf stable. They also don’t promote tooth decay, so they’re the sweetener of choice in many dental hygiene products, such as toothpaste and mouth rinse. On the downside, sugar alcohols may have side effects, especially when large amounts are eaten at one time. The most common complaints include gastrointestinal disturbances, such as abdominal pain, gas, bloating, and diarrhea.
Nonnutritive or noncaloric sweeteners include products that are hundreds to thousands of times sweeter than sugar. As a result, they can be used in such tiny amounts to sweeten foods that they’re essentially calorie-free. The safety of artificial sweeteners is highly controversial, although most health organizations, including the American Diabetes Association and the Academy of Nutrition and Dietetics, approve their use. In the United States, the Food and Drug Administration has approved the use of five artificial nonnutritive sweeteners—acesulfame K, aspartame, neotame, saccharin, and sucralose—in addition to one natural sweetener derived from the stevia plant, called rebaudioside A.65
Although rebaudioside A has been approved for use as a food additive (sweetener) in the United States, due to concerns about possible side effects, stevia itself has only been approved as a nutritional supplement. However, stevia is approved for use in several other nations and for several decades has been the principal nonnutritive sweetener used in Japan. Two recent scientific reviews found no health concerns associated with stevia.66,67 A third review reported that stevioside and related active compounds in stevia have antihyperglycemic, antihypertensive, anti-inflammatory, antitumor, antidiarrheal, diuretic, and immunomodulatory properties.68 However, stevia’s beneficial effects on blood glucose and blood pressure were observed only in participants whose markers for these conditions were elevated.
Opinion is somewhat mixed on the effectiveness of using nonnutritive sweeteners for weight loss, reducing carbohydrate intake, or controlling blood sugar. In reality, many people who consume foods and beverages that contain nonnutritive sweeteners make up for the missing calories by eating more. Although there’s been conflicting research,69 several large-scale studies have reported a positive correlation between artificial-sweetener use and weight gain.70 Some experts believe that this may be at least partly because the intensity of artificial sweeteners causes people to become desensitized to sweetness. Naturally sweet whole foods, such as fruits, may become less appealing, compared to less nutritious foods that contain powerful artificial sweeteners. Finally, research suggests that the body may have sweetness receptors in fat tissues. Nonnutritive sweeteners may actually trigger weight gain by stimulating the development of new fat cells.
The Bottom Line: Artificial sweeteners appear to offer no clear advantages to consumers and may have negative health effects. If a noncaloric sweetener is desired, products containing rebaudioside A appear to be the safest choice. Another option would be to use stevia leaf products judiciously. Sugar alcohols seem safe when used in moderation.
Although there’s some evidence that HFCS may have slightly more-pronounced adverse effects than sucrose when consumed in excess, the differences between the two most widely used sweeteners are relatively small. Sucrose is 50 percent glucose and 50 percent fructose. HFCS is either 55 percent fructose and 42 percent glucose (HFCS-55) or 42 percent fructose and 53 percent glucose (HFCS-42). Compared to a sweetener such as agave syrup, HFCS isn’t especially high in fructose; it’s just higher in fructose than regular corn syrup, which is mostly glucose.
Fructose molecules are the same, whether they come from sucrose, HFCS, or fresh fruit. However, in sucrose, the fructose and glucose molecules are chemically bound and must be cleaved by an enzyme or acid before being absorbed.62 In HFCS, both the fructose and glucose are present as free monosaccharides. Very preliminary evidence suggests that blood levels of fructose are higher when HFCS is consumed, compared to equal amounts of sucrose from beverages. Researchers also noted slightly higher uric acid and systolic blood pressures immediately following the consumption of beverages containing HFCS compared with those containing sucrose.63 The metabolic consequences of these differences over the long term are unknown, but they appear to be relatively small.
However, fructose does have more-damaging effects on the body than glucose, based on the scientific research to date. Because fructose doesn’t raise blood glucose levels significantly, consumers have been led to believe that fructose-rich sweeteners, such as agave syrup, are more-healthful choices, particularly for those with metabolic syndrome, prediabetes, or diabetes. However, fructose consumed in excess exceeds the body’s capacity to handle it. When the liver is presented with large volumes of fructose to process, it rapidly converts the fructose to fatty acids. Some of the fatty acids take up residence in the liver, while the remainder find their way into the bloodstream (as triglycerides) and then into fat cells. Also, of the adverse health effects of added sweeteners, many are even more pronounced with fructose.38,41,55
When consumers think of complex carbohydrates, grains often spring to mind. Grains, or cereal grains, are the edible seeds of grasses. Examples include wheat, oats, rye, corn, rice, barley, Kamut, spelt, millet, teff, and triticale. Although they’re also commonly referred to as grains and used in similar ways, the pseudograins, or pseudocereals, such as amaranth, quinoa, and buckwheat, are the seeds of nongrass plants; wild rice, which is the seed or fruit of an aquatic grain, is also classified as a pseudograin. Grains and pseudograins are key sources of both calories and protein for the majority of humans, as well as significant sources of fiber, B vitamins, several trace minerals, plant sterols, and phytochemicals.
According to the USDA 2010 Dietary Guidelines for Americans, grains are an important part of a healthful diet. The guidelines specify that at least half the grains consumed should be whole grains, and that refined grains be limited. In sharp contrast, many promoters of raw and low-carb diets declare that grains have no place on plates. Some claim that grains are not only unnecessary, but also that they’re inflammatory and acid forming, cause leaky-gut syndrome, impair mineral absorption, and are bad for joints, teeth, and skin. (It’s believed that gluten, a protein common to many grains, wreaks much of the havoc.) So, whose advice should consumers—and, more specifically, vegans—follow?
One way of approaching grain consumption is to choose other plant foods first (e.g., vegetables, fruits, legumes, nuts, and seeds) and tweak grain intake based on additional calorie needs. Low energy requirements would result in a low allowance for grains. Consumers whose energy needs are moderate or high can afford a more generous grain intake.
For the most part, the choice should be whole grains. The majority of studies that examine the health consequences of grain consumption have reported favorable effects for whole grains and unfavorable effects for refined grains. Less is known about the differences in health, if any, between people who consume whole grains and those who consume no grains, because few populations eschew grains as dietary staples. Grains make a significant contribution to total nutrient intakes while providing little fat and no cholesterol; their attraction is also due to their affordability, versatility, shelf stability, and energy content.
However, the proponents of low-carb diets aren’t completely misguided. Their advice likely springs from the fact that an estimated 90 percent of grains consumed by Americans are refined.71 There’s unanimous agreement that the rising consumption of refined grains has been an important contributing factor to overweight, obesity, and chronic diseases. Research suggests that diets rich in refined grains can result in a variety of adverse health consequences, similar to those associated with excess sugar consumption.3,4,72–75
On the other hand, although refined grains should be limited in the diet, eating a piece of pizza or dish of pasta—or making a batch of cookies with a little sugar—won’t sabotage a healthy diet. Indeed, occasional departures from whole foods can make a vegan diet more interesting, enjoyable, and inviting for nonvegan friends. However, for daily fare and optimal health, it’s best to choose whole grains over refined grains—and intact whole grains, such as barley or quinoa, instead of processed whole grains, such as bread or crackers made with whole-grain flour.
A diet may include flaked whole-grain cereal in the morning, whole-grain bread at lunch, whole wheat pasta at dinner, and brown rice cakes with almond butter as a snack. All are made from whole grains, but because they’ve been processed to varying degrees, they still aren’t the best choices for a healthy diet. Intact whole grains that have been sprouted or cooked provide the greatest return on investment.
The more whole grains are processed, the more their nutritional value diminishes. As a grain’s surface area increases, more of it is exposed to the air, increasing nutrient losses. Heat, light, and oxidation can destroy valuable vitamins, for example. Figure 5.2 (page 170) ranks processed grains from the most nutritious to the least. At the top are intact whole grains; their nutrient and phytochemical content can be further enhanced by soaking and sprouting them.76 Next are cut whole grains, followed by rolled and ground grains. At the bottom are flaked and puffed whole grains. Puffing makes grains so light and airy that they’re broken down by the digestive system very quickly; puffed grains have the greatest impact on blood sugar.
FIGURE 5.2. The whole-grain hierarchy
Sometimes fractions of whole grains, such as oat bran, wheat germ, and wheat bran, can still play a useful role in the diet. For example, wheat germ can boost the content of B vitamins and vitamin E in baked goods made with whole wheat flour. Oat bran can provide extra viscous fiber to the diet and can be helpful in controlling blood glucose or reducing cholesterol levels.
Gluten is a protein composite present in wheat, spelt, Kamut, rye, barley, and triticale (a hybrid of wheat and rye). Approximately 1 percent of the population suffers from celiac disease, a severe autoimmune response to gluten. For many years, patients who experienced adverse reactions to gluten but tested negative on celiac tests (blood tests to detect presence of antibodies and/or microscopic examination of intestinal tissue) were told that gluten likely wasn’t the cause of their symptoms. However, in 2011, a team of experts from the Center for Celiac Research at the University of Maryland School of Medicine released groundbreaking research suggesting that nonceliac gluten sensitivity is a distinct clinical entity, affecting roughly 10 percent of the population.77
In wheat, Kamut, and spelt, the proteins that combine to form gluten are gliadin and glutenin. Other proteins toxic to those with celiac disease are secalin in rye and hordein in barley. Oats don’t contain gluten and are safe for most people with celiac disease if they’re not contaminated by contact with wheat, rye, or barley. However, a small percentage of celiac patients is sensitive to a protein in oats called avenin and are unable to tolerate it. Although uncontaminated oats are becoming more widely available, most of the oats in North America are processed on the same machinery as other grains and, as a result, aren’t suitable for people with celiac disease.78–80
Although gluten sensitivity can generate symptoms similar to those caused by celiac disease, the effects are less severe. People with celiac disease experience inflammation and general damage to the small intestine, which causes flattening of the villi (tiny hair-like appendages that line the small intestine) and malabsorption of nutrients; those with gluten sensitivity don’t. Also, transglutaminase (tTG) autoantibodies show up in blood tests used to diagnose celiac disease; the bodies of people with gluten sensitivity don’t produce tTG.
However, gluten sensitivity appears to be part of a spectrum of gluten-related disorders and creates a measureable immune response with significant health implications. The research team noted there may be damage to other tissues, organs, and body systems in people with gluten sensitivity.77 As with celiac disease, symptoms often affect the gastrointestinal system (abdominal pain, cramping, bloating, diarrhea, and constipation), although they can cause problems in any body system. Behavior issues (depression, foggy mind, ADHD-like behavior, and autism), iron-deficiency anemia (fatigue, weakness, lack of concentration), joint pain, muscle disturbances, osteoporosis, leg numbness, migraines, and sinus problems are commonly reported.
When asked about what appears to be a sudden surge in gluten-related diseases, the study’s lead investigator and world-renowned expert on celiac disease, Dr. Alessio Fasano, pointed out that human bodies don’t have the enzymes to completely digest gluten, leaving undigested peptides that can be absorbed into the bloodstream with adverse health consequences for some individuals. Also, although controversial, he stated that grains have been bred to contain more gluten than in the past, and autoimmune diseases are on the rise, suggesting that it’s difficult for human bodies to adapt to a rapidly changing environment.81
Must people with gluten sensitivity completely avoid every trace of gluten in foods (as people with celiac disease must do)? The answer is not black and white, because sensitivity is on a continuum. For individuals with more severe sensitivity, gluten is best avoided completely. For those who are mildly sensitive, the occasional gluten-containing foods may not be a problem. Others may find that they can only tolerate gluten-containing grains if they’ve been sprouted (e.g., sprouted flour-free breads or sprouted grains for cereals and salads). Although sprouting does reduce the gluten content of grains, it doesn’t eliminate it. Gluten levels may also be lower in older varieties of wheat and in organic and fermented products (such as sourdough bread).
Even when gluten isn’t much of an issue, it’s wise to vary the grains eaten. Whole grains differ in their content of fiber, nutrients, and phytochemicals, so consuming a variety of grains, gluten-free grains (such as corn, job’s tears, millet, oats, rice, sorghum, and teff), and pseudograins (such as amaranth, buckwheat, quinoa, and wild rice) will provide a better balance of protective factors.
• Vary grain consumption. Include some pseudograins in the mix.
• Opt for gluten-free grains if gluten sensitivity is a factor. Use more squash, sweet potatoes, corn, and starchy vegetables for additional calories.
• Don’t regularly add wheat bran to foods; because it’s loaded with phytates (page 181), it can interfere with mineral absorption.
• Choose intact whole grains most of the time—sprout them for added nutrition.
• Use flaked and puffed whole grains sparingly.
• Limit intake of flour products, even whole-grain products.
When carbohydrate-containing foods are consumed, the body’s digestive enzymes break them into monosaccharides so they can be absorbed into the bloodstream. Two pancreatic hormones (insulin and glucagon) are responsible for regulating blood glucose levels. As blood glucose levels rise, the pancreas releases sufficient insulin to shuttle excess glucose into cells so it can be used for energy or stored for later use. When blood glucose dips too low, the pancreas releases sufficient glucagon to attach to liver receptor cells, triggering the conversion of enough stored glycogen to glucose to restore blood glucose levels. The actions of these two important hormones keep blood sugar levels stable, ensuring a continuous supply of fuel for body tissues, particularly the brain.
Choosing the right foods helps the body maintain good blood glucose control. This is especially important when the regulatory system is challenged, as with diabetes. Chronically elevated blood glucose levels accelerate development of the disease’s complications, including cardiovascular disease, blindness, neuropathy, kidney failure, and amputations. Foods with a lower glycemic impact can aid people with diabetes in controlling their disease, but they also provide advantages for healthy populations.
A recent meta-analysis of thirty-seven studies showed that diets with a high glycemic impact increased the risk of type 2 diabetes, heart disease, gallbladder disease, breast cancer, and all diseases combined.82 This study used two tools to assess the glycemic impact of the diet: glycemic index and glycemic load.
The glycemic index (GI) is a measure of the effect of carbohydrate sources on blood glucose levels. Carbohydrates that are slowly digested and absorbed release sugar molecules gradually into the bloodstream; they have a low GI. Carbohydrates that are quickly digested and absorbed into the bloodstream have a high GI. Foods with a high GI usually trigger a correspondingly high insulin response, adversely affecting long-term blood glucose control, increasing triglycerides, and reducing protective HDL cholesterol.83–85
In order for researchers to determine a food’s GI, a number of test subjects consume an amount of a food that provides 50 grams of carbohydrate. Changes in the subjects’ blood glucose are compared to changes in their blood glucose after they’ve consumed a control food (usually pure glucose) and then averaged to obtain the food’s GI. GI uses a scale of 0 to 100; 0 to 55 is low, 56 to 69 is medium, and 70 or more is high. Pure glucose has a GI of 100. White bread has a GI of 75, which means that the blood-sugar response to the carbohydrates in white bread is 75 percent of the blood-sugar response to pure glucose. By comparison, cooked barley has a GI of 28 relative to glucose.84
Sometimes these comparisons lead to interesting and surprising results. For example, sucrose has a GI of 65—lower than that of whole wheat bread, which has a GI of 74. The explanation lies in the types of sugar molecules that form the more-complex carbohydrates in bread; the starches in bread are chains of glucose molecules.
Monosaccharides (glucose, galactose, and fructose) don’t impact blood glucose equally. Fructose and galactose must first be transported by the bloodstream to the liver to be converted into glucose, glycogen, or fatty acids. As a result, their impact on blood glucose is about one-fifth that of glucose. In sucrose, half the sugar molecules are fructose, which reduces sucrose’s GI relative to pure glucose. On the other hand, although whole wheat bread may be more slowly digested and absorbed than sucrose, the glucose in bread causes a greater rise in blood glucose than the combination of glucose and fructose present in sucrose.
The GI figure produces a ballpark idea of how a serving of food that contains 50 grams of carbohydrate affects blood glucose. However, hardly any serving of food provides exactly 50 grams of carbohydrate, so a more practical tool, called the glycemic load (GL), was created to factor in the amount of carbohydrate actually eaten. A GL of 0 to 10 is low, 11 to 19 is medium, and 20 or more is high.
Foods that have a high GI don’t always have a high GL. GL is calculated by multiplying a food’s GI by the grams of carbohydrate provided in a serving and dividing the total by 100. For example, watermelon has a GI of 72; however, a 4-ounce (120 g) serving of watermelon provides only 6 grams of carbohydrate. Almost eight servings (2 pounds/960 g) of watermelon would be needed to yield 50 grams of carbohydrate.
That 4-ounce (120 g) serving of watermelon has a GL of 4 (GI of 72 times 6 grams of carbohydrate per serving divided by 100). When it comes to determining a food’s actual impact on blood glucose, the total amount of carbohydrate is just as important as its GI. Table 5.3 (page 176) provides the GI and GL of several common foods.
GI has frequently been used to judge the healthfulness of foods. Unfortunately, it conveys nothing about a food’s total nutritional content or any harmful contaminants or products of oxidation that may be present. Foods that contain little, if any, carbohydrate have a very low GI and a negligible GL. For example, meat—even processed meat or deep-fried meat—has a small impact on blood sugar. However, it has the potential to significantly increase insulin resistance and have adverse effects on blood glucose control over time.86–88
Further, unhealthy choices of carbohydrate-rich foods also can result from overreliance on their GI. For example, because fat- and salt-laden potato chips have a lower GI than a healthy baked potato, the chips would be selected. Other unhealthful snacks, such as candy bars, cupcakes, and ice cream, may also be viewed as acceptable because they frequently fall within the low-GI range due to their high fat content. Consumers may mistakenly shun nutritious, higher-carbohydrate whole foods (such as some fruits, starchy vegetables, and whole grains) because they have a relatively high GI.
Generally, foods aren’t eaten alone but in combinations; the choice of foods can have a profound effect on the meal’s overall glycemic impact. For example, baked potatoes have a high GI and GL. However, when eaten with the skin and accompanied by a black bean–peanut sauce (or a lentil loaf) and kale salad, a potato’s sugars are absorbed more gradually and the potato’s GI is blunted. In addition, the body benefits from the many other nutrients potatoes contain.
Although relying on a food’s GI and GL to make food choices has limitations, these indicators are helpful when appropriately used. For instance, compare the GI and GL of similar foods or foods of the same category: oatmeal versus cornflakes; the different intact grains, such as barley and millet; and rice milk versus soy milk (see table 5.3 on page 176).
Relative to the diets of nonvegetarians, vegan diets overall have a low GI and a low to moderate GL. One study that examined vegans’ GI and GL reported an average GI of 51 and an average total GL of 144 (the combined GL of all the foods consumed during the day).
This compares very favorably to nonvegetarian populations. In four large studies of nonvegetarians, average GIs ranged from 64 to 72 for participants who were in the lowest quintile of the study groups. One study also reported total GLs ranging from 117 for the lowest quintile to 206 for the highest quintile of the group. The authors suggested that the vegan population’s low GI and GL may be one factor that explains the lower risk of heart disease and type 2 diabetes in vegans compared to omnivores.89
Many foods are absent from the GI list because they’re either essentially free of carbohydrates (e.g., meat, poultry, and fish) or they don’t contain enough carbohydrates to make the GI test practical. Nonstarchy vegetables, such as leafy greens, broccoli, cauliflower, celery, peppers, and cucumbers, are good examples. To get 50 grams of carbohydrate from chopped broccoli, the test would require eating almost 9 cups.
As noted in the comparison between the GIs of sugar and bread, a food’s GI sometimes appears to be counterintuitive. Some of these factors help to explain such discrepancies:84,85,88,90–93
• Type of monosaccharide present. Glucose has a much greater impact on blood glucose than do fructose or galactose. Sweeteners with a lower GI contain more fructose, but this doesn’t make them a more healthful choice.
• Type of starch present. The two principal starches in foods—amylose and amylopectin—are digested at very different rates. Amylopectin, which constitutes about 70 percent of the starch in foods, is rapidly absorbed into the bloodstream; amylose is digested more slowly. Foods rich in amylopectin tend to have a high GI relative to foods rich in amylose. The remarkable range in GI of rice, for example, is due to its widely divergent amylose and amylopectin content. This explains why some varieties of low-amylose brown rice have higher GIs than some varieties of high-amylose white rice.
• Amount and type of fiber present. Fiber generally reduces the GI of a meal. However, foods rich in viscous fiber (e.g., beans and barley) reduce the meal’s overall GI to a greater extent than foods rich in nonviscous fiber, such as wheat bran. In addition, the GIs of high-fiber foods are generally lower than their refined counterparts. For example, if brown and white rice had the same amylose content, the brown rice would have a lower GI.
• Physical barrier. Beans and whole grains are surrounded by a fibrous coating that serves as a physical barrier to protect the seed. Because this barrier makes it more difficult for enzymes to digest them, these foods have a lower GI.
• Ripeness. As foods ripen, their starches turn into sugars, increasing their GI.
• Exposure to heat. Raw foods have a lower GI than the corresponding cooked foods. Cooking breaks down plant cell walls, increasing the rate at which their starches and sugars are absorbed by the body.
• Particle size. In smaller food particles, surface area is increased, allowing more-rapid digestion and absorption. For example, intact whole grains have a much lower GI than ground grains, whole fruits have a lower GI than fruit sauces or juices, and puréed beans have a higher GI than whole beans.
• Density. Foods that contain less air have a lower GI than light and fluffy foods. White bread has a higher GI than dense white pasta. Puffing grains also dramatically increases their GI.
• Crystallinity. Raw starch is crystalline—its molecules are organized in a sequence that repeats. Cooking disrupts this structure, making the starch more digestible and resulting in a higher GI. However, as the cooked starchy food cools, the starch recrystallizes to some extent, resulting in a lower GI. For example, red potatoes, cubed and boiled in their skin, have a GI of 89. Refrigerated overnight and eaten cold the next day, the same potatoes have a GI of 56.
• Acidity. Adding an acid, such as lemon juice or vinegar, to a food reduces its GI. Even small amounts of vinegar (less than an ounce) have been shown to reduce GI by about 30 percent. Fermentation produces acid, yielding foods with a lower GI. Yogurt has a lower GI than milk, and sourdough bread has a lower GI than regular bread.
TABLE 5.3. Glycemic index (GI) and glycemic load (GL) of selected foods
