The best way to choose the best fats is to choose the best foods in the right proportions. If you are expecting to find your way to better eating and health by selecting a single villain or savior, well—fat chance.
Consumers have questioned the relative health value of fats (or lack thereof) for decades. Many vegans consider the complete absence of animal fats and cholesterol as the nutritional trump card of plant-based diets. However, becoming vegan doesn’t guarantee healthful fat intakes. Although vegan diets generally keep saturated fat, trans-fatty acids, and cholesterol in check, there are concerns that they could fall short where essential fatty acids are concerned. In fact, some experts maintain that fish-free diets can’t provide optimal omega-3 fatty acid intakes. They advocate direct sources of long-chain omega-3 fatty acids for vegans and others who avoid fish.
Heated debates about the optimal amount of dietary fat rage on. Discussions surrounding the best sources of fat are no less intense, leaving vegan consumers with many unanswered questions. What are the differences among various fats, and which are the most valuable sources for vegans? Is coconut oil healthful or harmful? Should everyone heed the “no oil” message? Do vegans need to reduce their consumption of foods rich in omega-6 fatty acids when relying solely on plant sources of omega-3 fatty acids? What’s the optimal intake for vegans at every stage of life?
Lipids. Lipids are a family of organic compounds, most of which don’t dissolve in water. The most widely recognized lipids include fatty acids, solid fats and liquid oils (triglycerides), sterols (such as cholesterol), phospholipids (such as lecithin), fat-soluble vitamins and phytochemicals, and waxes. Although fats are only one type of lipid, the words fat and lipid are commonly used interchangeably.
Fatty acids. Fatty acids are basic components of fats and oils, as well as emulsifiers. Triglycerides have three fatty acid chains; mono- and diglycerides have one or two fatty acid chains, respectively. These chains of varying lengths are built of carbon atoms to which hydrogen and oxygen atoms are attached. Each fatty acid chain can be saturated, monounsaturated, or polyunsaturated, depending on the number of carbon atoms in the chain that could accommodate a hydrogen atom. A fatty acid chain with one open carbon atom is monounsaturated, while two or more open carbon atoms make the fatty acid polyunsaturated. A fatty acid chain with no open carbon atoms is saturated. Foods can contain varying amounts of saturated, monounsaturated, and polyunsaturated fatty acids, depending on the type of fat, oil, or emulsifier in that food.
Saturated fatty acids. The carbon chain of a saturated fatty acid can’t accept any more hydrogen atoms; all the carbon atoms have two hydrogen atoms attached. Saturated fatty acids occur naturally, although hydrogenation can turn a mono- or polyunsaturated fat into a saturated fat. Triglycerides that contain primarily saturated fatty acids are generally solid at room temperature.
A high intake of saturated fat has been linked to an increased risk of coronary artery disease (CAD) and insulin resistance, although this is a topic of considerable controversy.1–4 Animal products contribute a large percentage of saturated fat in Western diets. Approximately 20 to 30 percent of the fat in fish is saturated, as well as 33 percent in poultry, 40 to 44 percent in red meat, and 62 percent in dairy products. In most high-fat plant foods, only 5 to 20 percent of the fat is saturated. The exceptions are tropical oils. Coconut oil comprises about 87 percent saturated fatty acids, palm kernel oil about 85 percent, and palm oil about 50 percent.
Monounsaturated fatty acids (MUFA). Monounsaturated fatty acids have one spot in the carbon chain where hydrogen is missing (one point of unsaturation). Oils rich in monounsaturated fatty acids are generally liquid at room temperature but become cloudy and thick when refrigerated, as occurs with olive oil.
Monounsaturated fatty acids have been shown to have neutral or slightly beneficial effects on health, with modest effects on blood cholesterol levels. Replacing saturated fats, trans-fatty acids, or refined carbohydrates with monounsaturated fatty acids reduces total and LDL cholesterol and slightly increases HDL cholesterol.5,6 The richest dietary sources of monounsaturated fatty acids are olives, olive oil, canola oil, avocados, and nuts (except walnuts, butternuts, and pine nuts).
Polyunsaturated fatty acids (PUFA). Polyunsaturated fatty acids have more than one spot in the carbon chain where hydrogen is missing (more than one point of unsaturation). Oils high in polyunsaturated fatty acids are liquid both at room temperature and when refrigerated. There are two distinct families of polyunsaturated fatty acids—the omega-6s and omega-3s.
Polyunsaturated fatty acids generally have favorable effects on health. When they replace saturated fats, trans-fatty acids, or refined carbohydrates in the diet, total and LDL cholesterol levels decrease and HDL levels may slightly increase.7 The main dietary sources of polyunsaturated fatty acids are vegetable oils, seeds, nuts, grains, legumes, and other plant foods.
Essential fatty acids (EFA). Most fatty acids needed for survival can be produced in the body. However, two—known as essential fatty acids—can’t be synthesized and must be obtained from food: linoleic acid (LA) from the omega-6 family and alpha-linolenic acid (ALA) from the omega-3 family. The body uses LA and ALA to make highly unsaturated fatty acids (HUFA), critical building blocks for the brain, nervous system, and cell membranes. The balance between LA and ALA can have significant consequences for health, particularly for people who don’t consume direct sources of long-chain omega-3 fatty acids.
Cholesterol. The structure of every living cell requires cholesterol. Because the human body makes about 800 to 1,000 mg of this sterol each day, there’s no need for any dietary cholesterol. Although trace amounts are found in plants, dietary cholesterol mostly comes from animal products and is concentrated in eggs and organ meats. High intakes may increase the risk for chronic diseases, especially those of the heart and blood vessels.
Phytosterols. Phytosterols are sterols naturally present in plants. By competing with cholesterol during digestion, plant sterols help to block cholesterol absorption in the gut. All whole plant foods contain small amounts of these compounds, although vegetable oils, seeds, nuts, avocados, wheat germ, legumes, and sprouts are the most concentrated sources. Plant-based diets are naturally higher in phytosterols than omnivorous diets.
Hydrogenation. The process of hydrogenation adds hydrogen atoms to oils with polyunsaturated fatty acid chains; the hydrogen atoms attach themselves to the unsaturated carbon atoms. Hydrogenation converts the liquid oil to a semisolid or solid fat, such as margarine. The process is controlled to yield the melting point and other physical properties desired; most oils are only partially hydrogenated because complete hydrogenation would result in a saturated fat. Partially hydrogenated fats extend the shelf life of foods, increase the melting point of cooking fats (allowing higher-temperature cooking), and improve the texture and mouthfeel of products in which they are used.
Trans-fatty acids. Trans-fatty acids are created when the position of one hydrogen atom—added to an unsaturated carbon chain during hydrogenation—changes the original curved fatty acid molecule to a straighter molecule, which has a negative impact on cell membrane function. Approximately 90 percent of trans-fatty acids are formed during partial hydrogenation, which turns liquid oils into solid fats. (The other 10 percent naturally occur through the biohydrogenation of fats in the forestomach of ruminant animals.)
Vegetable oils were originally partially hydrogenated to serve as healthier substitutes for the animal fats they replaced, such as lard and butter. However, they’ve since been found to be even more damaging to human health than animal fats.8 Trans-fatty acids produced by hydrogenation strongly increase the risk of cardiovascular disease (CVD) by adversely affecting a multitude of risk factors.9–12 As a result, efforts are currently under way in North America to remove artificially produced trans-fatty acids from the food supply.
Trans-fatty acids found naturally in animal products don’t appear to be as damaging as those produced during industrial hydrogenation.11 However, evidence does suggest that these natural trans-fatty acids can impair insulin sensitivity in insulin-resistant individuals to a greater extent than manufactured trans-fatty acids.13 In addition, natural trans-fatty acids reduce HDL cholesterol and markedly increase both lipid peroxidation and the creation of free radicals.14 As a result, trans-fatty acids, both natural and artificial, should be avoided when possible.
Fat intakes vary a great deal among healthy populations around the world. The traditional diets of rural Asians commonly provide about 10 to 15 percent of calories from fat, while those of Mediterranean populations frequently exceed 35 percent of calories from fat.15,16 This variation holds true even among the five so-called “Blue Zones,” where large segments of the population remain healthy and active into their 90s and beyond. In Okinawa, Japan, traditional diets are very low in fat; in Loma Linda, California, and the Nicoya Peninsula of Costa Rica, fat intakes are moderate; in Sardinia, Italy, and Ikaria, Greece, diets are higher in fat. Although there’s no question that overall diet matters, the percentage of calories obtained from fat is clearly not a critical factor for health and longevity.1,17
So what do the diets of these protected people have in common? Residents of all the Blue Zones eat mostly plants. Highly processed fast foods and convenience foods are rarely used. Meat is reserved mainly for special occasions and isn’t consumed at all by the vegetarian Adventists in Loma Linda. Blue-Zone researcher and author, Dan Buettner states, “Beans, whole grains, and garden vegetables are the cornerstone of all these longevity diets.”18 In addition, residents of one or more of these areas include nuts, soy foods, antioxidant-rich spices, and dark wines in their diets. Figure 4.1 features a diagram of the lifestyle factors shared by three Blue-Zone populations (Okinawa, Loma Linda, and Sardinia). In Ikaria, Greece, the dietary cornerstones are vegetables (including potatoes and wild greens) and beans; meat and sugar intakes are low. In the Nicoya Peninsula of Costa Rica, corn tortillas, beans, and tropical fruits serve as the dietary staples.
FIGURE 4.1. Lifestyle factors of three Blue Zones
Source:272
The large variation in the percentage of calories from fat consumed by Blue-Zone populations and other healthy populations throughout the world is mirrored within vegan populations. At one end of the spectrum are the no-oil, super-low-fat followers, and at the other are the raw, no-grain, no-legume, avocado aficionados. Somehow, diets at both ends of the spectrum appear to do a reasonable job of promoting health, as long as the fat is of high quality and caloric intakes aren’t excessive.
Most major health organizations agree that fat intake should range from a low of 15 to 20 percent of total calories to a high of 35 percent. They also agree that saturated fats, trans-fatty acids, and cholesterol should be restricted.1,2,19
The World Health Organization (WHO) has set the population dietary intake goal for fat at 15 to 30 percent of calories. A slightly more generous upper limit of 35 percent of calories applies to highly active groups who consume diets rich in vegetables, legumes, fruits, and whole-grain cereals.19 In addition, a lower limit of 20 percent of total calories from fat is recommended for women of reproductive age. WHO also recommends that saturated fat intakes be less than 10 percent of calories (7 percent for high-risk populations) and trans-fatty acid intakes be less than 1 percent of calories.
In North America, the Institute of Medicine (IOM) hasn’t set a Recommended Dietary Allowance (RDA), Adequate Intake (AI), or Tolerable Upper Intake Level for total fat except during the first year of life. Instead, the Acceptable Macronutrient Distribution Range (AMDR) is applied.1 Based on evidence related to disease risk, the AMDR for fat varies by age and is indicated as a percentage of total calories:
• adults: 20 to 35 percent
• children (4 to 18): 25 to 35 percent
• children (1 to 3): 30 to 40 percent
• babies (6 to 12 months): 40 percent
• infants (birth to 6 months): 55 percent
The IOM report doesn’t set maximum levels for saturated fat, cholesterol, or trans-fatty acids, because disease risks caused by these factors increase no matter how much is consumed. However, the report does suggest eating as little of these compounds as possible, while consuming a diet adequate in other important essential nutrients.
The American Heart Association strongly advises that all Americans over the age of 2 limit fat to less than 25 to 35 percent of daily calories, saturated fat to less than 7 percent of daily calories, trans-fatty acids to less than 1 percent of daily calories, and cholesterol to less than 300 mg daily for most people (200 mg per day for people with CAD).2 Although the American Diabetes Association doesn’t suggest a range for total fat intake, it does recommend that people with diabetes keep saturated fat to less than 7 percent of total calories, minimize trans-fatty acids, and keep cholesterol intake under 200 mg per day.20
The IOM makes no separate recommendations for total fat intake for vegans—but there’s no reason to assume that the need for fats would be different from that of nonvegans. Limited evidence from studies on raw vegans suggests that higher total fat intakes can be consistent with health when the fat is derived from whole plant foods, such as nuts, seeds, and avocados.21–23 Fat intakes below 15 percent of total calories have proved safe and effective in Asian populations and in the treatment and reversal of chronic disease; however, this low level is generally not advised for healthy individuals and isn’t suitable for children or adolescents.
Table 4.1 provides target intakes for saturated, monounsaturated, and polyunsaturated fats at the various levels of fat intake. This guideline can easily be adjusted for higher or lower caloric intakes.
In conventional vegan diets, total fat intakes range from 18 to 36 percent of calories, averaging about 30 percent of calories.24 This compares to 36 percent of calories from fat in the average standard American diet.25 Although the average vegan’s 6 percent lower total fat intake is significant, the differences in the sources of fat in vegan diets, compared to omnivorous diets, are even more noteworthy.
Vegans consume no cholesterol and only about one-half the saturated fat that omnivores do. Trans-fatty acid intakes vary according to the inclusion of convenience foods, fast foods, and other highly processed foods that contain partially hydrogenated vegetable oils. Limited research comparing the trans-fatty acid intakes of omnivores, vegetarians, and vegans suggests that vegetarians consume slightly smaller amounts than omnivores, with vegans who eat whole-foods diets consuming negligible amounts.26
The total fat intakes of raw vegans average about 36 percent of calories, because these diets feature nuts and seeds as prominent sources of protein. Also, raw-food eaters tend to consume fewer starchy foods (e.g., grains, legumes, and starchy vegetables), so the proportion of calories from fat is higher.
TABLE 4.1. Approximate fat targets at differing fat intakes (2,000-calorie diet)
Some of the most well-respected vegetarian and vegan health authorities recommend limiting fat to no more than 10 percent of total calories.27–30 Their primary argument for very low-fat diets is that fat increases the risk of developing diseases, particularly chronic diseases, such as heart disease, type 2 diabetes, and certain cancers. Researchers have clearly demonstrated that, by reducing calories from fat to not more than 10 percent and also dramatically reducing harmful fats, heart disease can be successfully treated and, in many cases, significantly reversed.27,29,31 One study reported that low-fat vegan diets provide more effective therapy for people with type 2 diabetes than the conventional American Diabetes Association diet.30
Unfortunately, no studies exist that compare the effectiveness of very low-fat vegan diets to vegan diets with more-generous intakes of whole-foods fats. However, very low-fat diets have provided effective therapeutic intervention to thousands of people with life-threatening chronic diseases. Considering the extent to which these diseases have afflicted the population, the value of very low-fat diets can’t be overlooked.
Low-fat proponents strongly advise against the use of fats and oils. These foods aren’t necessary in a healthful diet, and eliminating them generally increases the nutrient density (amount of nutrients per calorie) of the diet. Note, however, that all Blue-Zone populations use some oil; Okinawans eat very small amounts, while Mediterranean populations consume more-generous quantities.
Advocates of very low-fat vegan diets also suggest minimizing the role of higher-fat plant foods. However, studies examining the health effects of eating higher-fat whole plant foods yield results that are overwhelmingly positive. In fact, eliminating or severely restricting high-fat plant foods may put some individuals at a disadvantage, so a lower limit of 15 percent of calories from fat is suggested for healthy vegan adults, with higher minimum intakes suggested for children. Other potential disadvantages of very low-fat diets should also be considered:
• Very low-fat vegan diets (10 percent or fewer total calories from fat) that exclude higher-fat plant foods and oils may not provide sufficient EFA quantities for optimal health. With the exclusive use of vegetables, fruits, grains, and legumes as fat sources, the EFA content (both omega-6s and omega-3s) of a very low-fat vegan diet is typically about half the IOM’s recommendations. Including higher-fat choices, such as soy products (e.g., tofu and soy milk), increases intakes, but EFA amounts may still fall short of the acceptable intakes (AI).
Although the implications of this shortfall are uncertain, it seems prudent for vegans to meet the AI for these nutrients. Adding approximately 1 ounce of seeds and/or walnuts to a diet with 10 percent fat would increase total fat to about 15 percent of calories in a 2,000-calorie diet. To meet the AI for both omega-6 and omega-3 EFAs, vegans should select seeds or nuts that provide a balance of both types of EFAs, (e.g., hempseeds or walnuts) or a combination of omega-3- and omega-6-rich products (e.g., flaxseeds plus pumpkin seeds, or chia seeds plus sunflower seeds).
• Absorption of fat-soluble vitamins (vitamins A, D, E, and K) and fat-soluble phytochemicals can be significantly reduced in very low-fat diets compared to diets with moderate amounts of dietary fat.1,32–35 Fat-soluble vitamins and phytochemicals are essential for health and play key roles in protecting against numerous diseases and health conditions. Including a small amount of fat in meals to maximize absorption of these protective elements ensures a truly optimal diet.
Low fat intakes also are associated with low intakes of zinc and some B vitamins, according to the IOM.1 Because zinc is a nutrient of concern in vegan diets—especially for children—it’s a good idea to include zinc-rich, higher-fat plant foods, such as nuts and seeds, in the diet.
• Very low-fat, high-carbohydrate diets can cause a decline in HDL cholesterol and a rise in triglyceride levels, particularly when the carbohydrates are refined. Low HDL cholesterol and high triglyceride levels are associated with an increased risk for CAD, metabolic syndrome, and type 2 diabetes.1,36
Increased triglyceride levels can be averted by avoiding refined carbohydrates and relying on carbohydrates from whole plant foods, such as legumes, vegetables, and whole grains. In vegans and other populations that consume low-fat plant-based diets, HDL levels are typically slightly lower than in the general population, yet risk for CAD is also low. Although very low-fat, whole-foods vegan diets can cause a further drop in HDL cholesterol, this is a natural consequence of total cholesterol reduction and may not result in increased health risk. Removing excess cholesterol from the bloodstream is HDL’s primary function; when there’s less cholesterol to remove, less HDL is needed, so less is produced.
• Very low-fat, high-fiber diets may provide insufficient energy, particularly for infants and children;1 adults with high energy needs may also find it challenging to eat enough calories on very low-fat diets.
The minimum level of fat necessary to support adequate growth and development in children is unknown. However, studies on omnivorous populations have found that in diets with adequate overall calories, as little as 21 percent of calories from fat is sufficient. It’s also unknown whether higher fat intakes would be needed in vegan children’s diets, which are higher in fiber and bulk. Studies of malnutrition in vegetarian and vegan populations have reported that highly fat-restrictive diets don’t adequately support children’s growth and development.37,38 One study of malnourished vegan infants noted that, by 14 to 16 months of age, their total calorie intake from fat was 17 percent.37
There’s also some evidence that a low-fat diet could cause chronic diarrhea in children.1 As a result, until additional research proves otherwise, it’s advisable for vegan children to stay within the AMDR for fat.
• Higher-fat plant foods provide valuable nutrients, including a variety of antioxidants (such as vitamin E and selenium), trace minerals, and a host of protective phytochemicals. But when consumers make avoiding fat their highest priority for food selection, their diets’ overall nutritional value may be reduced. By faithfully adhering to no-fat rules, they may choose less healthful products simply because they’re fat-free.
For example, pretzels and red licorice would be fair game, while fermented raw almond cheese and flax crackers would be off limits. A fat-free, sugar-based commercial salad dressing would be permissible, while homemade lemon-tahini dressing would not. Such trade-offs can diminish the value of a very low-fat diet.
High-fat diets (35 percent or more of total calories from fat) have long been thought to contribute to obesity and a variety of chronic diseases. However, some healthy populations have traditionally consumed diets that provide more than 35 percent of calories from fat. Good examples include Mediterranean populations and many raw-food adherents.39,40 Some leading health authorities promote Mediterranean-style diets as being optimal for health and encourage the liberal use of higher-fat foods, especially olive oil.39
In 1980, Ancel Keys’s classic Seven Countries Study reported a strong connection between subjects’ intakes of total fat and saturated fat and CAD.41,42 The link was unmistakable: as fat intake increased, so did rates of CAD. However, one group was an important exception—residents of the Greek island of Crete. In Crete, people averaged 37 percent of calories from fat, yet they had the lowest CAD rates among residents of all the nations studied—even lower than the Japanese, whose average fat intake was only 11 percent.
What separates the people of Crete (and other healthy Mediterranean populations) from less healthy populations that consume high-fat diets are their fat sources. The traditional Cretan diet includes abundant plant foods and olive oil; meanwhile, intakes of meat, poultry, and fish average less than 2 ounces per person per day. Religious practices also play a part in their diet. An estimated 60 percent of the study participants fasted during the 40 days of Lent; an unknown number also followed the Greek Orthodox Church’s dietary doctrines, which prescribe almost 180 days of abstention from meat, fish, dairy products, eggs, and cheese, as well as from olive oil on certain Wednesdays and Fridays.43 These practices weren’t mentioned or factored into the results of Keys’s study. However, leading experts from the University of Crete Faculty of Medicine believe that the regular restriction of certain foods—notably those of animal origin—had significant, positive health effects.43
Such Mediterranean-style diets provide a compelling argument that fat quality trumps quantity as a predictor of health outcomes when calories aren’t overconsumed. However, even when the fats consumed are predominantly mono- and polyunsaturated fats, excessive intakes may increase health risk. Some of the primary criticisms of high-fat diets include:
• Fats and oils, such as shortenings and vegetable oils, contribute significant calories but few nutrients or other protective components, such as fiber and phytochemicals. As a result, high-fat diets can dilute nutrient density, making it a challenge to meet recommended intakes for nutrients, especially those already marginal in the diet. Of particular concern are sources of trans-fatty acids, such as hydrogenated vegetable oils and foods prepared or manufactured with these fats.
• Some evidence exists that diets very high in fat (42 to 50 percent of calories from fat) may increase several markers of blood coagulation and thrombosis, potentially increasing the risk of heart disease.44,45 Other high-fat diets have been linked to chronic medical conditions, such as CVD, metabolic syndrome, type 2 diabetes, gallbladder disease, and some cancers. The weight of the evidence linking fat intake to these diseases is specific to diets rich in saturated fats and/or trans-fatty acids.1,19,46 However, intakes of these fats tend to be lower in vegan diets, and raw vegan diets completely avoid trans-fatty acids.
• The consumption of high-fat diets can increase overall energy intakes and induce weight gain.1 Fat has more than twice the concentration of calories as protein or carbohydrate, so more calories are easily consumed despite a smaller volume of food. For populations and individuals at high risk for overweight and obesity, more-moderate fat intakes are advised.
• Some evidence suggests that in consumers of high-fat diets, the body converts fewer EFAs to the more biologically active HUFAs, compared to lower-fat diets.47
• High-fat diets may result in increased oxidative damage to body tissues. Free radicals are more likely to react with the relatively unstable molecules in polyunsaturated fats,48 so people who consume greater amounts of these fats could be at increased risk. Oxidative stress has been linked to heart disease, cancer, type 2 diabetes, arthritis, age-related diseases, neurological disorders, and other illnesses.48,49
The science is crystal clear: a broad spectrum of fat intake can support and promote excellent health, but there are two important caveats. First, consumers must achieve energy balance, and second, they must select healthful sources of fat. If most of their dietary fat comes from whole or minimally processed plant foods, they can maintain excellent health even when fat intake is relatively high. On the other hand, when fats are derived from highly processed foods, fast foods, or convenience foods, negative health consequences can occur even with low fat intakes.
Strong evidence supports the use of very low-fat, plant-based diets as therapeutic treatment for chronic disease, particularly CVD. However, it’s not a foregone conclusion that all diets need to be so low in fat, that such diets set the gold standard for all vegans, or that very low-fat diets are suitable for all vegans.
Many factors need to be considered before establishing appropriate guidelines for fat intake in healthy vegan populations, because needs vary with the individual and change throughout the life cycle. Optimal fat intakes must support excellent health at every stage of life—including periods of rapid growth and development, such as pregnancy, infancy, and childhood—and must ensure excellent EFA status, adequate absorption of fat-soluble nutrients and phytochemicals, and smooth functioning of all body systems.
High-fat whole foods, such as nuts, seeds, avocados, and olives, aren’t responsible for the epidemic of chronic disease that plagues modern societies. In fact, higher-fat plant-based diets can promote health if these healthful sources of fats are chosen instead of processed fats and oils. Still, overly generous use of oil can dilute the nutritional quality of a plant-based diet; if used, intakes should be moderate.
In practical terms, to treat CVD, the very low-fat vegan diet is worth exploring, but a source of EFAs must be included (see pages 117 to 125). To combat overweight or obesity, a diet should minimize the concentrated sources of calories that provide few nutrients, including fats and oils. However, a moderate intake of nuts and seeds (e.g., 1 to 2 ounces per day) is consistent with healthy weight loss.
Vegans with a healthy body weight should focus on eating a variety of nourishing plant foods, including higher-fat plant foods. Small amounts of fresh-pressed oils can be included, but they’re not necessary for a healthful diet.
Necessary to survival are two essential fatty acids (EFA) that can’t be made in the body and must be obtained from food: linoleic acid (LA) and alphalinolenic acid (ALA). The body then constructs other complex fatty acids from LA, parent of the omega-6 (n-6) family, and ALA, parent of the omega-3 (n-3) family. LA and ALA are called parent fatty acids because it’s from them that the body produces highly unsaturated fatty acids (HUFA)—also known as long-chain polyunsaturated fatty acids (LCPUFA)—that make up each family. HUFA can be synthesized in the body by a series of elongation and desaturation reactions, or they can be obtained directly from food. (See figure 4.2 on page 118 for synthesis reactions and table 4.2 on page 119 for dietary sources of EFA and HUFA.)
For example, in the omega-6 family, LA can be converted to gamma-linolenic acid (GLA), dihommogamma-linolenic acid (DGLA), and arachidonic acid (AA). Or we can consume GLA directly from primrose, borage, or black currant seed oil, and AA directly from animal-based foods, such as meat and dairy products.
In the omega-3 family, ALA can be converted to stearidonic acid (SDA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). SDA can also be obtained directly from echium oil, black currant seed oil, hempseeds and hempseed oil, or fish. EPA and DHA can be consumed directly from fish (which contains both EPA and DHA), eggs (which contain only DHA), sea vegetables (which have small amounts of EPA), or microalgae (single-celled organisms that provide both EPA and DHA).
LA and ALA undergo a series of reactions that make these fatty acids more unsaturated (desaturation) and longer (elongation), which produces HUFA (see figure 4.2). The two fatty acids compete for the same desaturation enzymes, so an excess of one can reduce conversion of the other. ALA is usually favored in this process; however, there’s a point where an overabundance of LA relative to ALA can cause the conversion enzymes to become more occupied with omega-6 fatty acids, reducing ALA conversion to EPA and DHA.50–53
FIGURE 4.2. Metabolism of essential fatty acids
HUFA are more biologically active than EFA. They’re metabolized to produce a wide variety of hormone-like compounds that have a significant impact on multiple body functions, including blood clotting, blood pressure control, immune response, cell division, pain control, and inflammation response. The body produces dozens of different compounds from HUFA, including eicosanoids (prostaglandins, prostacyclins, thromboxanes, and leukotrienes), protectins, and resolvins.
Although the body needs eicosanoids from both families of fats, having a balance of the two is helpful, particularly in diets that don’t include direct sources of EPA and DHA. The eicosanoids formed within each family have somewhat opposing effects:
• Eicosanoids formed from the omega-3 derivative EPA tend to reduce platelet aggregation (stickiness of blood cells), improve blood flow, decrease cell division, and enhance immune function.
• Eicosanoids formed from the omega-6 derivative AA tend to increase platelet aggregation, decrease blood flow, increase cell division, and suppress immune function.
Protectins and resolvins are potent anti-inflammatory mediators; their names reflect their actions, because they protect against and resolve inflammation. They’re derived mainly from DHA, although a series of resolvins is also derived from EPA.54,55
The primary source of the two essential fatty acids, linoleic acid (LA) and alpha-linolenic acid (ALA), are plants from the land and sea. The richest sources are seeds and walnuts.
The most common dietary sources of highly unsaturated fatty acids (HUFA)—arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA)—are animal products (although DHA and EPA are also available from micro- and macroalgae). Table 4.2 provides a list of food sources of HUFA and table 4.6 (pages 131 and 132) lists specific amounts of these fatty acids in a variety of foods.
TABLE 4.2. Sources of polyunsaturated fatty acids
OMEGA-6 FATTY ACIDS |
OMEGA-3 FATTY ACIDS |
LINOLEIC ACID (LA) Corn kernels, corn oil Grapeseed oil Hempseeds and hempseed oil* Pine nuts/pignolia nuts Pumpkin seed oil Safflower seeds, safflower oil Sesame seeds, sesame seed oil Soybeans, soybean oil* Sunflower seeds, sunflower oil Walnuts, walnut oil* Wheat germ, wheat germ oil* GAMMA-LINOLENIC ACID (GLA) Black currant seed oil Borage oil Hempseeds, hempseed oil Primrose oil Spirulina ARACHIDONIC ACID (AA) Dairy products Eggs Fish Meat Poultry |
ALPHA-LINOLENIC ACID (ALA) Camelina oil Canola oil Chia seeds, chia oil Flaxseeds, flaxseed oil Green leafy land and sea vegetables Hempseeds, hempseed oil* Soybeans, soybean oil* Walnuts, walnut oil* Wheat germ, wheat germ oil* STEARIDONIC ACID (SDA) Black currant seed oil Echium oil Hempseeds, hempseed oil Seafood and fish EICOSAPENTAENOIC ACID (EPA) AND DOCOSAHEXAENOIC ACID (DHA) Breast milk Eggs** Fish and seafood, particularly cold-water oily fish Microalgae (plant DHA/EPA), but not blue-green algae Sea vegetables (less-concentrated EPA) |
*Hempseeds, soybeans, walnuts, and wheat germ are significant sources of both LA and ALA.
**Most eggs contain small amounts of DHA; eggs from chickens given feed rich in omega-3s contain greater amounts.
Where EFAs are concerned, vegan diets appear to offer no advantages over omnivorous eating patterns. Vegans could actually be at a disadvantage, because plant sources of omega-3 fatty acids are limited, and vegan diets are generally lacking in direct sources of omega-3 HUFA.56,57
Omega-3 fatty acids provide raw materials for building brains, nervous systems, and cell membranes (DHA is especially abundant in the retina, brain, and semen). They favorably affect the composition and functioning of cell membranes, enhancing intracellular signaling processes, gene expression, and the production of eicosanoids and cell mediators. There’s strong evidence that these fatty acids play key roles in the prevention and modulation of numerous disease processes, including CVD, hypertension, rheumatoid arthritis, autoimmune diseases, and several types of cancer. They may also protect against dementia, diabetes, and asthma, although the evidence for these conditions is weaker.55,58–62
Dietary ALA has a variety of possible fates once it’s absorbed into the bloodstream. Approximately 15 to 35 percent is rapidly converted to energy.63 ALA can also be incorporated into cell membranes, stored in fat tissue for later use, or converted into ketone bodies; the carbon fragments can be recycled to make saturated and monounsaturated fatty acids.
The balance is converted into omega-3 long-chain polyunsaturated fatty acids (HUFA). Conversion efficiency is unpredictable, varying among individuals, with stages of life, and in different body tissues.1,61,64 An estimated average of 5 percent of ALA converts to EPA and less than 0.5 percent to DHA, although several studies have suggested higher conversion rates.61,65 ALA’s rate of conversion to EPA can range from about 0.3 percent to as much as 21 percent, while the rate of conversion to DHA ranges from zero to about 9 percent.66,67
Consuming direct sources of DHA, such as fish or eggs, depresses the final step in conversion from EPA to DHA by 70 percent or more.66,68 (In other words, not consuming direct sources of DHA is known to enhance the rate of conversion. This is the body’s way of maintaining sufficient HUFA in the absence of direct dietary sources.) DHA itself can be converted back to EPA at a rate of up to 12 percent.69,70
The body’s conversion of ALA is limited by multiple factors, some of which are unrelated to diet. The most significant nondietary factors—gender and genetics—are outside of our control. Being female appears to provide an advantage in ALA conversion, particularly during the childbearing years. There’s considerable evidence that estrogen boosts DHA synthesis in preparation for pregnancy or lactation.71 During this stage of life, the rate of ALA conversion to both EPA and DHA is at the upper end of the conversion range. One study found young women converted a remarkable 36 percent of ALA to HUFA (21 percent to EPA, 9 percent to DHA, and 6 percent to an intermediary highly unsaturated fat called DPA).67 The same study group reported that conversion rates in young men averaged 16 percent (8 percent to EPA, 8 percent to DPA, and zero to DHA).66 However, genetic variations in desaturase enzymes can slow conversion in some individuals.64,72,73 Other nondietary factors that adversely affect ALA conversion include smoking, advancing age, and chronic disease (e.g., diabetes, metabolic syndrome, hypertension, and hyperlipidemia).74–76
Dietary factors can have a profound influence on ALA conversion (see table 4.3). The most potent factor—high intakes of omega-6 fatty acids—can reduce conversion by as much as 40 to 60 percent.77–79 Trans-fatty acids can also inhibit conversion, as can excessive intake of alcohol and caffeine.80 Nutritional inadequacies, such as protein deficiency or a lack of vitamins and minerals—especially zinc, magnesium, niacin, pyridoxine, and vitamin C—can diminish the activity of conversion enzymes.75,81,82
Although fasting may reduce ALA conversion, low-fat or calorie-restricted diets appear to enhance conversion.75 One study compared two similar controlled diets, equal in calories and having similar omega-6 to omega-3 ratios, but differing in fat and carbohydrate content. The principal difference between the diets was that one was relatively low in fat (about 20 percent of calories from fat) while the other was high in fat (45 percent of calories from fat).47 Study investigators found that the lower-fat diet produced much more favorable ALA conversion than the high-fat diet. (See table 4.3 for a summary of the factors most strongly affecting n-3 conversion).
Direct sources of SDA have been shown to raise both EPA and DHA concentrations more effectively than ALA consumption.80,83 Although SDA isn’t abundant in the food supply, it accounts for about 12 to 14 percent of the fatty acids in echium oil, 3 percent in black currant seed oil, and 2 percent in hempseed oil.84–86 Echium oil comes from a plant called Purple Viper’s Bugloss, which is native in parts of Europe but invasive in America and Australia.
TABLE 4.3. Factors affecting ALA conversion
NONDIET FACTORS |
EFFECTS |
Genetics |
Genetic variations in desaturase enzymes can reduce conversion. |
Gender |
Women of childbearing age are more-efficient converters than men, possibly due to differences in sex hormones. |
Age |
Conversion is reduced with advancing age. |
Smoking |
Smoking depresses desaturase enzymes, slowing conversion. |
Chronic disease |
Diabetes, metabolic syndrome, hypertension, and hyperlipidemia (elevated blood lipids) can adversely affect conversion. |
DIET-RELATED FACTORS |
|
Omega-6 fatty acids |
High intake can reduce conversion by 40 to 60%. |
Poor nutrition |
Protein deficiency and suboptimal intakes of vitamins (niacin, pyridoxine, and vitamin C) and minerals (zinc and magnesium) can reduce conversion. |
Very high-fat diets |
Diets very high in fat (45% fat) appear to diminish conversion relative to lower-fat diets (20% fat). |
Direct sources of SDA |
Direct sources of SDA enhance conversion relative to ALA. |
Changes in the human diet during the last century have affected intakes of the two essential fatty acids, LA and ALA, altering the natural balance that previously existed. Experts estimate that until about 100 to 150 years ago, most diets provided omega-6 and omega-3 fatty acids in a ratio of approximately 1:1.60 Research suggests that, at this ratio, conversion to long-chain polyunsaturated fatty acids (HUFA) would be significantly higher. This makes sense. If the body couldn’t convert ALA to EPA and DHA, humans wouldn’t be able to survive without fish, seaweed, and other foods rich in these fatty acids. A century ago or more, inland residents may not have had regular access to these foods, so conversion must have been adequate and appears to be related to the balance of EFA in their diets.
Since then, enormous changes in the food supply have pushed the ratio of omega-6s to omega-3s to 10:1 and higher.24,71,87 In vegan diets, the balance is even more precarious, ranging from 8:1 to 18:1,24 due to increased LA intakes commonly associated with today’s plant-based diets. These intake levels can adversely impact growth and development, cell membrane function, inflammatory reactions, and numerous disease processes.60,62
There’s still considerable debate about whether the ratio of omega-6s to omega 3s should be a matter of concern. However, conversion efficiency has been shown to be significantly affected by this ratio.88 As a result, awareness of the ratio is useful for vegans and others who don’t consume sufficient EPA and DHA from direct sources, and who rely solely on conversion of ALA to meet their need for EPA, DHA, and other omega-3 HUFA. The ratio is less relevant for nonvegetarians, who consume direct sources of HUFA, such as fish.89
Although the optimal ratio of LA to ALA for efficient conversion is uncertain, international recommendations—which assume some direct intake of long-chain fatty acids—range from a low of 2:1 to a high of 10:1.56 Although vegans are well-advised to keep intakes within this range, there’s convincing evidence that conversion is more efficient at the lower end of the range.60,87,90
A recent Canadian study found that, in a diet providing 1 percent of energy from ALA, an LA to ALA ratio of 4:1 resulted in higher amounts of EPA and lower amounts of AA than a diet with an LA to ALA ratio of 10:1.90 An earlier study also found that a ratio of 4:1 allows for adequate conversion in healthy vegetarians.91 Two additional research groups reported that optimal conversion was achieved with ratios of 2.3:1 and 2:1, respectively.92,93 Finally, a Japanese research team reported significant improvements in conversion with a shift from soy oil to a high-ALA oil called perilla oil.94 This change reduced the omega-6 to omega-3 ratio from 4:1 to 1:1 and increased EPA by 44 percent and DHA by 21 percent. A few other studies have shown significant increases in DHA with increased ALA intake; however, most of the studies have been of short duration and few have used diets with such a low omega-6 to omega-3 ratio. Other experts have also suggested that a ratio of 1:1 maximizes conversion,75,87 but modern diets make it challenging to achieve this ratio. Based on the evidence to date, ratios ranging from 2:1 to 4:1 seem a reasonable target for vegans.56
Although it’s not common, it is possible for vegans to overconsume omega-3 fatty acids. If individuals avoid nuts, seeds, avocados, and other high-fat plant foods but eat large amounts of flaxseeds, flaxseed oil, or chia seeds, the reduced proportion of omega-6s to omega-3s could result in an unfavorable ratio of 1:2 or more. (For example, flaxseed oil has a remarkable omega-6 to omega-3 ratio of 0.28:1 and averages about 57 percent alpha-linolenic acid.) This would reduce the conversion of LA to AA, potentially leading to omega-6 deficiency. Symptoms include dry hair, scaly skin, dry eyes, joint pain, brittle nails, and increased risk of chronic disease.
Intakes of LA tend to be somewhat higher among vegans than nonvegetarians, while total ALA intakes are similar for vegans, vegetarians, and nonvegetarians (less than 1 to 3 grams per day).52,56,61,95 Not surprisingly, intakes of long-chain omega-3 fatty acids vary widely: vegans consume negligible amounts, lacto-ovo vegetarians consume small amounts, and omnivores consume higher amounts, as determined by their level of fish intake. The average intake of EPA and DHA in the United States is approximately 100 mg per day.57
The majority of scientific studies that assess vegan EFA status have reported lower levels of EPA and DHA in blood, plasma, and platelets. However, vegan DHA status appears not to diminish as people age, suggesting an ongoing, constant level of conversion, however low.62 Among nine studies reporting reduced levels in vegans compared to omnivorous controls, EPA ranged from 12 to 79 percent that of the controls, while DHA ranged from 32 to 67 percent. On average, EPA and DHA levels in vegans were about half that found in omnivores.52,62,95–101 It’s interesting to note that levels of EPA and DHA in vegans were significantly lower in older studies (1978 to 1992) than newer studies (1994 to the present). It’s unclear whether this is due to changes in analytic methods for measuring omega-3 status or recent improvements in dietary intakes of EFA.
However, one study found omega-3 fatty acid status wasn’t reduced in vegans.61 The UK EPIC-Norfolk study assessed the EFA intake and status of almost 5,000 men and women from different dietary groups, including meat eaters, fish eaters, lacto-ovo vegetarians, and vegans. Unfortunately, there were only 10 vegans in the study (after supplement consumers were excluded). It’s possible that results derived from this small group aren’t a true reflection of the status of the wider vegan population or that the vegans in this study weren’t completely vegan (they were assigned to their dietary group based on a seven-day food record).
Although the vegans in this study had lower intakes of all omega-3 fatty acids compared to the nonvegans, differences in the plasma levels of EPA and DHA between the two groups were not as great. In male vegans, plasma levels of EPA and DHA were 113 and 81 percent that of fish eaters, respectively. In female vegans, plasma levels of EPA and DHA were 77 and 106 percent that of fish eaters, respectively. The investigators suggested that vegan conversion rates from ALA to EPA and DHA were approximately twice that of other dietary groups (for example, 209 percent higher in vegan men and 184 percent higher in vegan women than in fish eaters).
To reduce CVD risk, the 2010 Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans recommends eating 8 ounces (240 g) or more of seafood each week. There’s no question that fish eaters have much higher intakes of EPA and DHA than vegans, because fish is the most concentrated dietary source of these HUFA. Vegans normally consume almost no EPA or DHA unless they eat fortified foods or use supplements.
However, the evidence to date isn’t terribly convincing that a diet that includes fish yields a distinct advantage over a vegan diet. Although observational studies do suggest that diets rich in omega-3 fatty acids (especially EPA and DHA) reduce cardiovascular events, the results of clinical trials are less clear.103 Although adding EPA and DHA to vegan diets may provide cardiovascular benefits, evidence comparing heart disease rates of fish eaters and vegans is very limited.
In a 1999 meta-analysis comparing vegans, lacto-ovo vegetarians, fish eaters, and meat eaters, vegans had the lowest body fat, blood pressure, and blood cholesterol levels of all the dietary groups. However, mortality rates from heart disease were lower among lacto-ovo vegetarians and fish eaters than vegans. (Compared with meat eaters, mortality rates were 34 percent lower among lacto-ovo vegetarians and fish eaters, and 26 percent lower among vegans.)104
More recently, EPIC-Oxford investigators reported that vegetarians (including vegans) had a 32 percent lower risk of heart disease than other dietary groups when results were adjusted for all confounding variables except BMI, and a 28 percent lower risk when BMI was factored in. In this study, fish eaters had the same rates of heart disease as meat eaters.105
The reputed cardioprotective effects of fish are tied to its EPA/DHA content. Vegans and others who avoid fish have the option of getting EPA and DHA from cultured microalgae supplements. Unlike fish, cultured microalgae are free of heavy metals, such as lead, mercury, and cadmium, and industrial pollutants, such as polychlorinated biphenyls, DDT, and dioxin. Considering the increasing demands for EPA and DHA, and the rapid decline in fish species and stocks, consuming alternative sources of long-chain omega-3 fatty acids makes good sense. (See pages 15 to 18.)
Although this study is encouraging, a larger study showed different results. EPIC-Oxford, a UK cohort with a larger number of vegan participants, reported on the EFA status of 659 men, including 232 vegans.62 In these vegans, plasma EPA was 47 percent and plasma DHA was 41 percent that of meat eaters. Although the vegan men’s plasma EPA and DHA concentrations were low, they were quite stable over time (anywhere from one year to twenty years).62 As a result, further investigation is needed about EFA conversion rates in vegan populations.
Finally, a group of investigators from the United Kingdom found that vegans’ breast milk contained about 38 percent of the DHA found in the breast milk of omnivores. In this study, the omega-6 to omega-3 ratio was about 18:1 in the vegans compared to about 10:1 for the omnivores.102
The IOM hasn’t set an RDA for EFA because of a lack of evidence for determining actual requirements.1 However, the IOM has set the Adequate Intake (AI) for LA at 12 grams a day for women and 17 grams a day for men. The AI for ALA is 1.1 grams a day for women and 1.6 grams a day for men.1 These Als aren’t designated as optimal intakes but are simply a reflection of median intakes in a population in which EFA deficiencies are considered essentially nonexistent. The IOM has also set an AMDR of 5 to 10 percent of energy from LA and 0.6 to 1.2 percent of energy from ALA.1,106–109
The WHO recommends that 5 to 8 percent of calories come from omega-6 fatty acids and 1 to 2 percent of calories from omega-3 fatty acids106 (this corresponds to an ALA intake of 2.2 to 4.4 grams per day in a diet that provides 2,000 calories). Meanwhile, many health authorities recommend direct intakes of EPA and DHA in the range of 250 to 550 mg per day.107–109 For example, the European Food Safety Authority proposed dietary reference values of 10 grams of LA and 2 grams of ALA plus 250 mg of EPA and 250 mg of DHA for adults, 100 mg of DHA for infants 7 to 24 months of age, and an additional 100 to 200 mg of DHA for pregnant and lactating women (above the 250 mg of DHA already suggested for adults).110 Although the IOM hasn’t set AIs for EPA and DHA, a panel of experts convened in 2008 to reassess this position recommended that the AI for EPA and DHA be set between 250 and 500 mg per day.107
No separate official EFA recommendations exist for vegans, vegetarians, or other consumers who don’t eat fish. Although many national health authorities have recommended intakes for EPA and DHA, vegans can’t meet these levels without using supplements. But, would vegans benefit by taking DHA and EPA supplements? Unfortunately, we don’t yet know the answer.
Considering that men and postmenopausal women convert ALA less efficiently, it’s possible their needs for omega-3 fatty acids are modest and serve mainly to support cell membrane turnover. In addition, DHA is the most highly unsaturated fat in the diet and also the most easily oxidized by free radicals in the blood. Because oxidized fats can contribute to disease processes, it’s possible that the body avoids making DHA when it’s not needed. On the other hand, conversion is enhanced in women of childbearing age, particularly those who are pregnant or lactating, because more DHA is needed—the developing fetus requires at least 400 mg of DHA per week during the last trimester.71
So, although conversion to EPA and DHA is generally slow and incomplete in vegans, it appears to be sufficient to meet the needs of most healthy people if their ALA intake is adequate and their diet is well balanced.62,87,88 Yet, it’s possible that vegan health outcomes could be improved by adding direct sources of long-chain omega-3 fatty acids. More research is required to help clarify this issue.
Although it’s unknown if vegans would benefit by adding supplemental DHA (and possibly EPA), there’s a clear inverse association between direct EPA and DHA intake and CVD risk. There’s more limited evidence for an inverse association between direct EPA and DHA intake and depression, cognitive decline, and age-related macular degeneration107,111–115
Some evidence exists for improvements in infants’ visual acuity, growth, development, and cognition with higher maternal DHA intakes during pregnancy and lactation, and during the first two years of life.116–118 (These benefits are more pronounced in poorly nourished children.118) Nonetheless, research on the growth and development of vegan children has failed to reveal any demonstrated deficiencies in visual or mental development when care has been taken to ensure they eat sufficient calories and get adequate amounts of vitamin B12.88 In addition, although there’s limited data on cognitive function in vegan adults, one study reported an average IQ of 119 in 118 vegan men.
Because moderate increases in omega-3 fatty acid intake are generally considered safe and potentially beneficial, it seems prudent for vegans to take steps to optimize omega-3 fatty acid status. (See pages 117 to 125.)
Consuming sufficient omega-3 fatty acids can be ensured by increasing intakes of ALA relative to LA or by adding a direct source of DHA, and possibly EPA, to the diet. Increasing ALA intake can be an effective strategy for boosting conversion to EPA and DHA, but the body’s capacity for conversion is limited, and genetic variations in metabolism can compromise conversion in some people.72,119 Instead, adding direct sources of DHA or DHA plus EPA effectively increases omega-3 status.69,88,120–123
One small trial showed that taking 200 mg of DHA for three months increased DHA in the plasma of male vegans by 50 percent.122 However, the primary vegan sources—DHA- and EPA-rich microalgae supplements or fortified foods—may not be affordable or available to everyone, so there are limitations to both these options (in addition to wildly differing opinions as to which option is preferable for vegans). Considering the uncertainty and the need for further research, the decision is a personal one.
The following suggestions for increasing EFA intake can be regarded as informed guesses based on a careful examination of the literature and discussions with leading international experts. Some authorities suggest a minimum 1.5 grams of ALA per day for optimal health, which exceeds the current AI for women.124,125 When relying almost exclusively on ALA for omega-3 fatty acids, vegans should base the intake amount on double the current AI.56 Using North American AIs, vegan men should consume 3.2 grams of ALA per day, while vegan women should obtain 2.2 grams per day. (See table 4.4 for suggested intakes for all age groups.) Doubling the AI would require a parallel increase in the AMDR for ALA to 1.2 to 2.4 percent of calories. The AMDR for LA would remain unchanged at 5 to 10 percent of calories.
Of course, augmenting ALA intake doesn’t guarantee optimal EFA status, although it helps to ensure that sufficient raw materials are available for conversion to long-chain polyunsaturated fatty acids (HUFA). Alternatively, vegans could include direct sources of DHA, and possibly EPA, aiming for about 10 percent of the AI for ALA (see table 4.4). Individuals who regularly consume a direct source of DHA wouldn’t need to increase ALA over the current AI. A more affordable option would be to add a 200 to 300 mg DHA (and possibly EPA) supplement two to three times a week.
TABLE 4.4. Adequate Intake (AI) of omega-3 fatty acids and suggested intakes for vegans
Source:1
*Not applicable; infants will get DHA from breast milk (or appropriate commercial formula).
To ensure the availability of sufficient long-chain omega-3 fatty acids for infants, it’s wise to breast-feed for two years and beyond. If breast-feeding stops before the baby is 12 months old or if formula is used as the primary milk, select a milk or formula with added DHA. Once the baby begins consuming fortified full-fat soy milk (sometime after 1 year of age), a supplement providing 70 mg of DHA per day could be introduced, if desired. For pregnant and lactating women, several expert panels and health authorities have recommended DHA intakes of at least 200 to 300 mg per day,126–128 so this level seems reasonable for vegans as well.
A bit of a buzz surrounds the possible link between ALA and the risk for prostate cancer and degenerative eye diseases. This has raised concerns because vegans rely on ALA-rich foods (such as walnuts, flaxseeds, hempseeds, and chia seeds) as primary sources of omega-3 fatty acids. However, there’s likely no cause for concern among vegans who get their ALA from whole plant foods or from oils that have been stored and used in ways that minimize damage to ALA.
Of twenty-three studies assessing the relationship between ALA and prostate cancer risk, eleven reported that higher intakes and/or higher tissue or blood levels of ALA are positively associated with prostate cancer.129–139 The remaining twelve studies found either no association or an inverse association between intake, tissue or blood levels of ALA, and prostate cancer.140–151
In addition, six meta-analyses reviewed the evidence on ALA and prostate cancer risk.152–157 Of these, one study reported no significant association between ALA and prostate cancer risk;152 three studies found a weak protective effect of ALA;154–156 and two studies found ALA was associated with increased prostate cancer risk, although the association wasn’t significant in one study, and after adjustment for publication bias, the positive association was eliminated in the other study.153,157
Three reports have assessed the risk for degenerative eye diseases, such as cataracts and age-related macular degeneration, in participants of the Nurses’ Health Study. These studies all found positive associations between ALA intake and risk for eye diseases. A 2005 study found that those with the highest ALA intakes (1.26 grams of ALA per day) had slightly more than double the risk of cataracts compared to those with the lowest ALA intakes (0.86 grams per day).158 A 2007 report on the same cohort found a 16 percent increase in lens nuclear density (a risk factor for cataracts) in those who consumed the greatest amounts of ALA compared to those with the lowest intakes.159 Finally, another 2007 study of participants older than 50 found that the highest ALA consumers had a 41 percent increased risk of age-related macular degeneration compared to those with the lowest intakes.160
Why do some reports show an increased risk of prostate cancer and degenerative eye diseases in people who consume greater amounts of ALA? Experts suggest that the answer may lie in the dietary sources of the ALA. In the United States and many other Western countries, the primary dietary sources of ALA are meat and other animal products. Other sources include processed foods made with ALA-containing oils, such as soybean oil and canola oil (e.g., mayonnaise and margarine), and foods fried or cooked using these oils. Considering these sources of ALA, it’s quite possible that ALA itself is not the issue, but rather ALA damaged by heat, light, oxygen from food processing, and high-temperature cooking. Researchers have also suggested that ALA may simply be a marker for high meat and fat intakes, as well as unhealthful eating patterns.152
Conversely, walnuts, ground flaxseeds, hempseeds, and chia seeds weren’t major sources of ALA in these studies, raising confidence that vegans have no cause for concern. In fact, a small handful of studies by one research team in the United States found that adding 3 tablespoons (45 ml/30 g) of ground flaxseeds per day consistently decreased prostate cancer cell proliferation in men with prostate cancer, compared to men who didn’t consume ground flaxseeds.161–163
In addition, the high ratio of omega-6 to omega-3 fatty acids diminishes the conversion of ALA to EPA and DHA, both of which may protect against degenerative eye diseases.164 In this case, improving the ratio by reducing omega-6 fatty acids and increasing omega-3 fatty acids would help to solve the problem. A final possible explanation is that those who consumed the highest amounts of ALA may not also have consumed sufficient quantities of antioxidants to preserve and protect these fragile fatty acids. Western-style diets centered on animal products and processed foods are notoriously low in antioxidants. A variety of whole plant foods, such as leafy greens and other colorful vegetables and fruits, is needed to obtain these protective dietary compounds.
The Bottom Line: Based on the science to date, the evidence doesn’t warrant any adjustment in suggested ALA intakes for vegans (see table 4.4 on page 127 for suggested intakes for all age groups). It’s also very important that ALA sources are of high quality and are protected from damage in storage and during cooking.
To improve EFA status, vegans should take the necessary steps to achieve an omega-6 to omega-3 ratio that maximizes conversion of ALA to EPA and DHA. They also may wish to consider adding a direct source of DHA (and possibly EPA). To reach the suggested ratio of 2:1 to 4:1, the goal is approximately 5 to 10 percent of calories from LA and 1.2 to 2.4 percent from omega-3 fatty acids. In a 2,000-calorie diet, this would be 11 to 22 grams of LA and 2.7 to 5.3 grams of ALA. (See table 4.5.) Individuals with increased needs or decreased capacity for conversion may need to boost intake of ALA to the upper end of this range (2 to 2.4 percent of calories) and keep LA near the lower end of this range (5 to 8 percent of calories). In a 2,000-calorie diet, this would be 11 to 18 grams of omega-6 fatty acids and 4.4 to 5.3 grams of omega-3 fatty acids.
TABLE 4.5. Essential fatty acid content of selected plant foods
Finding the right balance between getting 5 to 10 percent of calories from polyunsaturated fats and achieving a desirable ratio of omega-6s to omega-3s of 2:1 to 4:1 can be relatively simple. A very low-fat diet should include enough seeds to meet minimum EFA needs. A diet that includes more liberal amounts of fat should focus on foods rich in monounsaturated fatty acids, such as avocados and nuts, with the addition of some more-concentrated omega-3-rich foods. (A higher-fat diet also can include fresh or dried coconut, which is almost exclusively saturated fat with few omega-6 and no omega-3 fatty acids.)
Vegans can ensure adequate EFA intakes with a diet based on whole foods, provided that a rich source of omega-3 fatty acids to balance the omega-6s in these foods is included. (See table 4.6.) Avocados, olives, and nuts (except for walnuts, butternuts, and pine nuts) are concentrated sources of monounsaturated fatty acids, although they contain saturated fatty acids and LA as well. Each ounce of nuts provides an average of 1 to 3 grams of omega-6 fatty acids.
Seeds, seed oils, and soybeans are principal sources of polyunsaturated fatty acids, both omega-6s and omega-3s. Both walnuts and hempseeds provide a good balance of omega-6 to omega-3 fatty acids, but hempseeds also provide small amounts of SDA, which converts more readily to longer-chain omega-3 fatty acids than ALA. Flaxseeds are a rich and economical source of ALA. (Because whole flaxseeds tend to go undigested through the gastrointestinal tract, they should be ground before being eaten.) Chia seeds also are an excellent source of ALA, though they can be pricey.
Oils rich in omega-3 fatty acids are unstable and have a low smoke point, so they shouldn’t be used for cooking. Instead, they should be eaten or served uncooked (for example, in salad dressings). Good choices are cold-pressed flaxseed oil, hempseed oil, or balanced oils that include plenty of omega-3 fatty acids (often these oils have a 1:1 or 2:1 ratio of omega-6 to omega-3 fatty acids). Liquid Gold Salad Dressing (page 219) provides a delicious way to boost omega-3 fatty acid intake.
Grains, legumes, vegetables, and fruits are generally very low in fat, so they make fairly minor contributions to fatty acid intake. One exception is soy foods, such as tofu and soybeans, which derive more than 40 percent of their calories from fat. The fat in grains is predominantly omega-6 fatty acids, although the ratio of omega-6 to omega-3 fatty acids varies considerably. For example, oats have a ratio of 22:1, while it’s 13:1 for wheat, 10:1 for brown rice, 9:1 for barley and quinoa, 4:1 for rye, and only 1.25:1 for wild rice. Greens provide more omega-3s than omega-6s. Legumes and fruits contain mainly polyunsaturated fatty acids, with some being higher in omega-6 fatty acids and others higher in omega-3 fatty acids. Legumes average a ratio of about 1:1 with a few notable exceptions, such as chickpeas with a ratio of 26:1 and lentils with a ratio of about 4:1. The average ratio for fruit rests somewhere between 1:1 and 2:1, with apples at about 5:1 and papayas at about 1:5.
TABLE 4.6. Fatty acid composition of selected foods
*For convenience, peanuts are included in the nuts and seeds category; peanuts are a legume.
The following guidelines are useful in putting together a diet that ensures an excellent intake and balance of essential fatty acids:
• Follow the guidelines in chapter 14 to ensure a healthful, nutritionally adequate diet. Eating sufficient protein, vitamins, and minerals maximizes the body’s ability to convert ALA to long-chain polyunsaturated fatty acids (LCPUFA). Avoid trans-fatty acids and excess consumption of alcohol or caffeine; these can reduce conversion efficiency.
• Include good sources of ALA daily. The richest plant sources of ALA are seeds (chia seeds, flaxseeds, flaxseed oil, hempseeds, and hempseed oil) and walnuts. (Although most of the fatty acids in leafy greens are omega-3 fatty acids, the total fat content in raw greens is so low that 10 cups provide just 1 gram of ALA.) Individuals who don’t use DHA/EPA supplements should aim for 1.2 to 2.4 percent of calories from ALA (about 3.2 grams of ALA for men and 2.2 grams for women). Using DHA/EPA supplements lowers the need for dietary ALA to 0.6 to 1.2 percent of calories (1.6 grams of ALA for men and 1.1 grams for women). (See table 4.4 on page 127 for suggested intakes for various age groups.)
• Reduce intake of omega-6 fatty acids, if excessive. Regular use of cooking oils rich in omega-6 fatty acids, such as sunflower, safflower, corn, grapeseed, or sesame oil, can result in excessive consumption of these fatty acids. Also, many processed foods, such as salad dressings, margarines, crackers, cookies, and other high-fat foods, rely on omega-6-rich oils. Substitute oils that are mainly monounsaturated, such as extra-virgin olive oil, organic canola oil, or high-oleic sunflower oil, or oils with a high monounsaturated fatty acid content, such as safflower oil. Although these oils still provide omega-6 fatty acids, the omega-6s are present in much smaller quantities. For example, 1 tablespoon of omega-6-rich oil has about 7 to 10 grams of LA, compared to about 1 gram in 1 tablespoon of olive oil and 2.7 grams in 1 tablespoon of canola oil (the canola oil also provides about 1.3 grams of omega-3 fatty acids, for an excellent ratio of 2:1).
Eating large quantities of seeds or nuts that are low in omega-3 fatty acids (e.g., sunflower seeds, pumpkin seeds, sesame seeds, and pine nuts) could also push omega-6 intake above recommended levels. To keep omega-6 fatty acids under control, minimize the use of omega-6-rich oils and limit consumption of omega-6-rich seeds and pine nuts to about 1 ounce per day in a 2,000-calorie diet. Balance larger quantities of omega-6-rich foods with increased omega-3s accordingly.
Although the fatty acids in most nuts and avocados are mainly monounsaturated, these foods do contribute to omega-6 intakes. Most nuts contain about 1 to 3 grams of omega-6 fatty acids per ounce (pecans have almost 6 grams), while an avocado half provides less than 2 grams. Most grains are also far higher in omega-6 than omega-3 fatty acids. So, including some concentrated omega-3 sources when consuming these foods can help to bring omega-6 fatty acids into balance.
• Consider a direct source of DHA, and possibly EPA. Although it’s not essential to use supplements or fortified foods that provide direct DHA (and possibly EPA), there’s good evidence that doing so effectively boosts omega-3 fatty acid status. As noted previously, adequate DHA levels may be especially important during pregnancy and lactation and for individuals who have difficulty with ALA conversion (e.g., those with hypertension or diabetes). (See table 4.4 on page 127 for suggested intakes.)
The most common sources of EPA and DHA are fish and seafood; the only plant sources are plants from the sea—microalgae and seaweed. Seaweed doesn’t contribute significantly to EPA intakes in the West but is a significant source in nations where people use large quantities of seaweed daily (e.g., Japan and other parts of Asia). Although seaweed does contain small amounts of highly unsaturated omega-3 fatty acids, it’s even lower in fat than most vegetables. A 100-gram serving provides about 100 mg of EPA, but little DHA. In addition, some varieties of seaweed may provide excessive iodine if consumed in large quantities (See table 6.1 on page 194.)
Blue-green algae (spirulina and Aphanizomenon flos-aquae [AFA]) are low in highly unsaturated omega-3 fatty acids. Spirulina is rich in GLA—a beneficial omega-6 fatty acid—while about 40 to 50 percent of the fat in AFA is the omega-3 fatty acid ALA. Although neither type of blue-green algae is a significant source of EPA or DHA, some research indicates that they may promote more-efficient omega-3 conversion than plants grown on land.167
Microalgae-based vegan supplements are the most promising source of ecologically sustainable long-chain omega-3 fatty acids. These supplements, which provide DHA or DHA plus EPA, are widely available but are relatively expensive. For most people, an intake of 100 to 300 mg per day (or just two to three times a week) is reasonable. Microalgae-based DHA is also being added to some soy milks, cold-pressed oils, juices, cereals, and other foods, although the amounts are relatively small.
Many people aren’t sure whether to stick to straight DHA or opt for combination DHA/EPA supplements. DHA is necessary for the development and maintenance of brain and eye function and is most important during pregnancy, lactation, and infancy. Because conversion from ALA to DHA can be limited, adequate intake of DHA appears more critical during these life stages. However, there may be further benefits to consuming supplements that combine DHA and EPA. EPA plays an important role in reducing chronic inflammation and may protect against some mental disorders. Both EPA and DHA appear to support heart health. As a result, a combination supplement may be most appropriate.
As the Roman philosopher Seneca noted, “It is quality rather than quantity that matters.” With regard to fat, the evidence that quality is more important than quantity has become increasingly convincing, particularly when energy intakes aren’t excessive.
All fats in nature (whether from plants or animals) contain a mixture of saturated, monounsaturated, and polyunsaturated fatty acids; the relative amounts depend—at least in part—on climate. In plants, both fluidity and stability are critical. Generally speaking, in plants found closer to the equator, a greater proportion of their fat is saturated. For example, coconuts and palm fruits are high in saturated fatty acids to help protect and preserve the plants. Avocados and olives grow in more moderate climates and contain relatively stable monounsaturated fatty acids. In plants that grow in cold climates, polyunsaturated fatty acids often predominate to retain fluidity; a good example is flaxseeds. We see this in animals, as well. For example, warm-water fish are generally higher in saturated fat compared to cold-water fish, which contain much greater amounts of the highly unsaturated fatty acids, EPA and DHA.
Although the relative amounts of saturated, monounsaturated, and polyunsaturated fatty acids in foods have implications for human health, we’re beginning to discover that other factors (such as how people process, store, and prepare foods, and how much they eat relative to their energy needs) may weigh more heavily. Although fat was once regarded as a dietary villain, it’s now viewed as a valuable part of the whole food package.
The highest-quality fat is present in fresh, whole, and minimally processed plant foods. All plant foods contain some fat, although nuts, seeds, avocados, coconuts, and olives are the most concentrated fat sources in any plant-based diet. One of the reasons that the fat in these foods is so beneficial is that it’s unaltered and is protected from rancidity by naturally present antioxidants. In addition, whole plant foods are neatly packaged with protective components, such as proteins, unrefined carbohydrates, fiber, phytochemicals, plant sterols, and a variety of vitamins and minerals.
Plant-food fats are largely unsaturated, with the exception of coconut and palm fruits, whose fats are predominantly saturated. Although excessive consumption of saturated fats has been linked to increased disease risk, there’s little evidence that suggests adverse effects when moderate amounts are consumed as part of a whole-foods, plant-based diet.
Conversely, meat and dairy products are rich in the type of saturated fats most strongly linked to increased blood cholesterol levels and insulin resistance.274,275 The presence of cholesterol in these foods is thought to exaggerate the impact of their fats. Evidence also suggests that eating animal fats increases the risk of colorectal cancer.169
Clean fish is widely considered one of the best fat sources, due to the significant content of the long-chain omega-3 fatty acids, EFA and DHA, in the fat. However, high-fat fish—especially those at the top of the food chain, such as King mackerel, tuna, swordfish, and shark—also can be a key source of environmental contaminants, including mercury, which diminishes their overall value.
Regardless of whether they’re derived from plant or animal sources, fats that have been chemically altered by food-processing techniques or exposed to high temperatures pose particular concern. Among the most damaging to health are fats that have been chemically altered and solidified via partial hydrogenation, resulting in the creation of harmful trans-fatty acids. These fats are implicated in many disease processes; they raise blood cholesterol levels, trigger inflammation, increase insulin resistance, and compete with essential fatty acids for incorporation into cell membranes.
Unfortunately, based on a belief that partially hydrogenated vegetable oils were more healthy than animal fats, food manufacturers liberally used partially hydrogenated fats—with their trans-fatty acids—for several decades before research revealed their dark side. Governments are now actively trying to reduce and, in some cases, eliminate trans-fatty acids from food supplies.
When any fats or oils are heated to temperatures of 350 to 400 degrees F (177 to 204 degrees C), their smoke points often are exceeded, allowing mutagenic products of oxidation to form. It’s safest to avoid deep-fried foods and minimize the use of oils when cooking over high heat.
Generally, refined oils are more heat stable than unrefined oils, because they contain fewer of the solid particles that burn easily. However, the refining process itself can damage fat molecules, and it removes most of the protective components associated with the whole food. Unrefined oils (which can be a source of healthful fats when properly stored) have smoke points as low as 200 to 225 degrees F (93 to 107 degrees C); they’re best reserved for salads and other unheated foods.
The longstanding view that saturated fats are “bad” has recently come under fire. At the core of the controversy are studies suggesting that saturated fat may not increase risk of heart disease.170–171,273 Two key reports sent shock waves throughout the scientific community. The first was a 2010 meta-analysis of twenty-one studies by Siri-Tarino and colleagues, which investigated the relationship between saturated fat intake and CVD in almost 350,000 people.171 The second was a 2014 meta-analysis of seventy-six studies by Chowdhury and colleagues, which involved more than 510,000 people.273 Contradicting decades of national and international dietary recommendations, no clear association between saturated fat intake and these diseases was found. A media frenzy ensued, leading consumers to believe that saturated fat had been vindicated and that beef, butter, bacon, and brie could be eaten with abandon.
Why did these large meta-analyses show no significant relationship between saturated fat and heart disease? First, many of the studies included in these meta-analyses compared similar populations that ate Western-style diets high in both fat and saturated fat (studies that examine a more diverse range of saturated fat intakes tend to show more significant disparity in disease risk); even the lowest intakes of saturated fat were above recommended intakes. Second, many of the studies used in these analyses relied on a single twenty-four-hour recall to determine dietary intakes; this method isn’t reliable for ascertaining long-term dietary patterns. Third, several of the studies were adjusted for serum cholesterol levels. Because serum cholesterol concentrations increase with higher intakes of saturated fat, controlling for this variable obscures the results.
Since the mid-1990s, a dozen meta-analyses and scientific reviews have examined the relationship between saturated fats and CVD.170–181,273 Of these studies, nine reported that saturated fat increased CVD risk.173–181 In 2010, the US Department of Agriculture Dietary Guidelines Advisory Committee summarized the evidence regarding the effects of saturated fat intake on risk of CVD and type 2 diabetes. They concluded that evidence supporting saturated fats’ harmful effects is very high, and that replacing just 5 percent of saturated fats in a diet with polyunsaturated fats will decrease risk for CVD and type 2 diabetes and improve insulin response.182 A 2011 consensus statement from an expert panel (convened to review the evidence regarding saturated fat and CVD) came to the following conclusion: “The evidence from epidemiological, clinical, and mechanistic studies is consistent in finding that the risk of coronary heart disease is reduced when saturated fatty acids (SFA) are replaced with polyunsaturated fatty acids (PUFA). In populations who consume a Western diet, the replacement of 1 percent of the energy from SFA with PUFA lowers LDL cholesterol and is likely to produce a reduction in coronary heart disease incidence of ≥ 2 to 3 percent.”274 (It’s interesting to note that two of the coauthors of the Siri-Tarino meta-analysis were among the experts on this panel.) Finally, a 2012 Cochrane review reported that reducing saturated fat lowered the risk of cardiovascular events by 14 percent.173
Clearly, the media don’t always tell the whole story. In the case of the Siri-Tarino analyses, the media reported that saturated fat had been vindicated. In fact, the study showed that when saturated fat is replaced by trans-fatty acids or refined carbohydrates, there’s no improvement in cardiovascular risk—and, in the case of trans-fatty acids, risk is significantly heightened.
For many years, consumers were told that replacing saturated fats with carbohydrates would effectively reduce CVD risk because carbohydrates lower LDL cholesterol. More recently, however, research studies are suggesting that replacing saturated fat with refined carbohydrates (e.g., white flour products, white rice, and sugar-sweetened beverages and treats) provides no advantage and may actually increase CVD risk relative to saturated fat.172,174,183,274 Although refined carbohydrates reduce LDL cholesterol, they also reduce HDL cholesterol and increase triglyceride levels.
More research is required to determine the relative effectiveness of unrefined carbohydrates as a replacement for saturated fat,183 although populations consuming diets low in saturated fat and high in unrefined carbohydrates are well protected against CAD. Evidence suggests that diets containing carbohydrate sources with a low GI are beneficial,184 as are diets rich in unrefined carbohydrates.186,187
We asked Dr. Francesca Crowe, one of the coauthors of the 2014 Chowdhury meta-analysis, about the weight of the evidence concerning saturated fat and CVD risk. She responded, “The best available evidence (from randomized controlled trials) shows that saturated fat intake affects blood cholesterol levels, which is an important risk factor for heart disease. Therefore, current guidelines should still recommend that people minimize their intake of saturated fat.” The take-home message remains the same as it was thirty years ago: Western-style diets rich in animal products and processed foods increase CVD risk, while diets based on high-fiber, whole plant foods (such as vegetables, legumes, fruits, whole grains, nuts, and seeds) are protective.
Some people take a hard-line view against all fat, including the fat found in whole plant foods. However, hundreds of scientific studies have confirmed that high-fat plant foods not only deserve a place in diets, but also that they deserve a place of honor. The research on these foods provides a powerful rebuttal to criticisms leveled against higher-fat plant foods in vegan diets.
Although nuts are sometimes vilified for their high caloric content, they offer remarkable dietary and health benefits. Adding nuts to a diet enhances the quality of the diet, while improving intakes of multiple nutrients and protective dietary components.188,189
Nutrient-dense nuts are brimming with beneficial vitamins and minerals. They’re important sources of vitamin E and contribute to niacin, thiamin, riboflavin, pantothenic acid, vitamin B6, and folate intakes. They’re also valuable sources of trace minerals, such as iron, zinc, copper, calcium, selenium, magnesium, manganese, potassium, and phosphorus, and are very low in sodium (unless they’re salted).
Nuts are among the most naturally antioxidant-rich foods (especially walnuts, pecans, hazelnuts, pistachios, and almonds) and also are rich in lignans, phytosterols, ellagic acid, and many other bioactive compounds. Due to their low carbohydrate content, nuts (as well as seeds) have the lowest glycemic index (GI) and glycemic load (GL) of any whole plant food. (For more on GI and GL, see pages 172 to 178.)
Most of the calories in nuts come from healthful fats, predominantly monounsaturated fatty acids (except for walnuts and pine nuts, which are high in polyunsaturated fatty acids), and nuts are low in saturated fats and free of trans-fatty acids and cholesterol. They’re also are good sources of plant protein and particularly rich in L-arginine. This amino acid is a precursor of nitric oxide, which helps to preserve the elasticity and flexibility of blood vessels, enhancing blood flow.
As a result, nuts offer some protection from CVD and can enhance longevity. In several population groups, the frequency of nut consumption has been found to be inversely related to all causes of death;190 regular nut-eating is estimated to increase longevity by about two years.191 Moderate intakes of 1 to 2 ounces per day are associated with maximum benefits.
In 2011, a large research study compared a variety of metabolic markers for CVD, type 2 diabetes, and metabolic syndrome in nut consumers versus nonconsumers. The data was derived from the 1999–2004 National Health and Nutrition Examination Survey (NHANES), in which more than 13,000 American adults participated.189 Results showed that, compared to nonconsumers, participants who ate nuts had a lower body mass index (BMI), lower body weight, smaller waist circumference, lower systolic blood pressure, reduced incidence of hypertension, higher HDL cholesterol levels, reduced fasting blood glucose, and lower rates of metabolic syndrome. This data supports the authors’ conclusion that nut consumption decreases multiple risk factors associated with these diseases. Other studies have reported favorable effects of nuts on the risk of developing diabetes192–194 and metabolic syndrome.189,193,195
In addition, nuts appear to protect against coronary heart disease (CHD). Two large review studies released in 2010 reported the wide-ranging cardiovascular and metabolic benefits of nut consumption, including significant risk reduction for CHD.196,197 Four major population studies (the Nurses’ Health Study, the Physicians’ Health Study, the Iowa Women’s Health Study, and the Adventist Health Study) also linked regular nut consumption to an extraordinary 35 to 50 percent risk reduction in CHD.198–203 Of sixty-five food items examined in the Adventist Health Study-1, nuts provided the greatest protection against CHD, reducing deaths due to CHD by more than 50 percent in participants who consumed nuts five or more times a week, compared to those who ate nuts infrequently.204
Dozens of research studies have noted the beneficial effects of eating nuts on blood cholesterol levels.188,196,205–209 Not only do nuts lower LDL cholesterol and raise HDL cholesterol, but they also appear to normalize the more-harmful, small, dense LDL particles that damage the cells lining blood vessels.210 In addition, preliminary evidence suggests that compounds in nuts protect against inflammation and oxidized LDL and promote endothelial function.211,212
According to data from the Nurses’ Health Study, substituting calories in the form of the fat in 1 ounce of nuts for an equivalent amount of calories from carbohydrates would reduce coronary heart disease (CHD) risk by about 30 percent; replacing saturated fat with the equivalent amount of nut fat would reduce risk by about 45 percent.180 These researchers estimated that people who eat nuts every day may gain an extra five to six years of life free of CHD.
Nuts may also be useful in the prevention and treatment of stroke,213,214 dementia,215,216 gallstones,217 and advanced macular degeneration.218
An ongoing concern about nuts is that they might contribute to overweight and obesity. However, population studies have reported either no association or an inverse association between nut intake and BMI or body fat.198,219–222 Various clinical trials have recorded little or no weight change when various types of nuts are included in diets.188,195,207,208,223–225
A number of possible mechanisms may explain this unexpected phenomenon.188,226,227 First, nuts appear to promote satiety, in turn reducing caloric intake from other foods. Second, some evidence indicates that nut consumption increases resting metabolic rate. Third, research suggests that bodies don’t efficiently extract all the calories nuts provide, and that a considerable portion of nut fat is excreted in the feces. One research team suggested that, combined, these three mechanisms offset about 55 to 75 percent of the energy (calories) provided by nuts.227
A common question is whether raw or roasted nuts offer more nutritional benefits. Most population studies don’t distinguish between raw and roasted nuts (or nut butters), and both types have been shown to afford protection. However, roasted nuts contain acrylamide and other products of oxidation that could potentially reduce their beneficial effects.228 For example, acrylamide begins to form in almonds when their internal temperature reaches approximately 266 degrees F (130 degrees C),229 and commercial nut-roasting temperatures are generally 285 to 300 degrees F (140 to 150 degrees C).230 Of course, nut butters also can have added fats, sugar, and salt, so read the label.
Either roasting or soaking nuts results in reductions in phytate content. However, soaking and sprouting nuts increase the content and availability of their protective components, such as phytochemicals and antioxidants; the enzymes released by soaked nuts liberate these beneficial nutrients without forming acrylamide. Soaked nuts are crunchy and delicious but are perishable and should be refrigerated and used within a few days (for more on storing nuts, see sidebar, page 145). Soaked nuts can also be dehydrated and used the same way as roasted nuts.
Less research has been conducted on seeds than on nuts. Consequently, their value in human nutrition is often underestimated. Seeds vary in their protein content from about 12 percent of calories to more than 30 percent of calories; in contrast, the total protein in nuts ranges from about 4 to 15 percent of their calories. Seeds are among the richest sources of vitamin E and provide an impressive array of other vitamins, minerals, and phytochemicals, as well as fiber. This concentrated food also is the most plentiful source of healthy fatty acids. Pumpkin seeds, sunflower seeds, poppy seeds, hempseeds, sesame seeds, and tahini are rich in omega-6s, while flaxseeds, chia seeds, hempseeds, and canola seeds are high in omega-3s.
Flaxseeds are particularly high in ALA, so their consumption can go a long way toward correcting an imbalance between omega-3 and omega-6 fatty acids. Flaxseeds also provide a number of other nutrients. They’re the richest known source of lignans (preliminary evidence suggests lignans may help to reduce growth of human cancer cells)231,232 and are also one of the best sources of boron. In addition, they’re very high in soluble fiber. Studies show that eating flaxseeds can help to reduce blood cholesterol levels233 and improve a number of other markers of CAD.234–236
Like other plant foods, flaxseeds contain a variety of antinutrients, such as phytic acid, oxalates, and cyanogenic glycosides. These compounds don’t pose a health risk to most individuals, and consuming moderate amounts of raw flaxseeds (1 to 2 tablespoons per day) or larger amounts of cooked flaxseeds is safe for most people.237 However, the body converts cyanogenic glycosides into substances that can block the uptake of iodine by the thyroid gland when iodine intake is inadequate (see pages 191 to 194).
Meanwhile, chia seeds, both whole and sprouted, are rapidly gaining popularity in raw-food cuisine. They’re the only food higher in omega-3 fatty acids than flaxseeds; as much as 64 percent of chia oil comprises omega-3 fatty acids,238 compared to an average of 57 percent in flaxseed oil. Chia seeds are packed with antioxidants and don’t appear to contain the antinutritional factors found in flaxseeds.
The nutritional value of hempseeds is no less remarkable. About 20 percent of their calories come from easily digestible, high-quality protein,239 and eating them provides an impressive array of trace minerals, vitamins, and phytochemicals. Hempseed oil has an excellent balance of omega-6 to omega-3 fatty acids and is one of the few foods that provide both SDA and GLA (page 117). (As a bonus, hemp may well be the most environment-friendly crop that can be grown. It takes only about one hundred days to mature, can be planted in the same fields year after year, and requires no pesticides or fertilizers. Besides providing nutritious seeds, the plant can be used to make more than 25,000 different products.)
Most people know avocados are rich in monounsaturated fatty acids, but they may be surprised to learn about avocados’ high levels of nutrients, fiber, and phytochemicals. Avocados contain more folate and potassium per ounce than any other fruit (60 percent more potassium than bananas) and are a good source of vitamins C and E. As a high-fiber food, the average avocado (about 200 grams) provides 13.5 grams of fiber—the equivalent of about three medium-sized apples.165
Avocados are rich in carotenoids and, of all commonly eaten fruits, have the highest concentration of lutein.240 They also contain 76 mg of beta-sitosterol per 100 grams of fruit—more than four times that of other commonly eaten fruits, and double the amount in other whole foods.241 (Plant sterols, such as beta-sitosterol, possibly inhibit tumor growth and can inhibit cholesterol absorption from the intestine, helping to reduce blood cholesterol levels.241) Avocados are also among the richest sources of glutathione, a powerful antioxidant.
Unfortunately, clinical data on the health effects of avocado consumption is limited. One study examined its effects on women’s blood lipid levels, comparing an avocado-enriched diet (with avocados providing approximately 37 percent of the calories from fat and 20 to 35 percent of the total calories) with an American Heart Association-III (AHA-III) diet (approximately 20 percent of calories from fat, 100 to 150 mg of cholesterol, and high amounts of complex carbohydrates).242 Participants consumed each of the diets for three weeks.
Participants’ total cholesterol dropped an average of 4.9 percent while on the AHA-III diet and 8.2 percent on the avocado-enriched diet. There was no significant difference in their HDL cholesterol levels between the pre-entry diet and the avocado-enriched diet. However, HDL cholesterol dropped 13.9 percent when participants switched from the pre-entry diet to the AHA-III diet and 12.8 percent when they switched from the avocado diet to the AHA-III diet, suggesting that avocados contribute to maintaining HDL levels.
Studies also suggest that blends of bioactive compounds derived from avocados may provide benefits in cancer prevention and treatment and in reducing certain inflammatory diseases.243 One study group reported that carotenoids and tocopherols in an extract of avocado inhibited the growth of human prostate cancer cells in vitro;240,243 lutein alone was unable to reproduce these effects. Investigators also showed that avocado extract selectively induced death in human oral cancer cells, specifically blocking two key components in the cancer pathway.244,245 Finally, a research team from India reported that the phytochemicals in avocados selectively inhibit growth and induce cell death in both precancerous and cancerous cell lines, and they show potential as chemoprotective agents to lower the side effects of certain chemotherapy drugs.246
Preliminary evidence exists that avocado extract acts against Helicobacter pylori, the bacteria associated with ulcers and stomach cancer.247 Avocado extract also has been shown to provide anti-inflammatory effects, with some evidence suggesting reduction in the symptoms of knee and hip osteoarthritis.248,249
Cultivated from antiquity, olives are a cherished part of the Mediterranean diet, and for good reason. They’re a rich source of monounsaturated fat; a good source of iron, copper, and vitamin E; and rich in phytosterols as well as a host of beneficial phytochemicals, particularly polyphenolic compounds.250,251 For example, oleuropein, the major polyphenol in olives, is a potent free radical scavenger, inhibiting oxidative damage in body cells and protecting heart tissue.252
Both olives and olive oil contain bioactive compounds with known anticancer effects, including lignans, squalene, and terpenoids.253 Extra-virgin olive oil is also rich in a polyphenol called oleocanthal, an anti-inflammatory agent.254
Are olives more nutritious than olive oil? Certainly; as a whole plant food, olives contain fiber and a variety of nutrients. Fermented olives also can be a good source of friendly bacteria. Olive oil does have the advantage of being much lower in sodium, although the sodium content of olives varies with the curing method. However, olive oil has 120 calories per tablespoon, while a serving of ten large olives contains only 50 calories.
The availability of olives has grown dramatically. A few decades ago, only two types of olives were commonly available—canned black olives and green olives (usually stuffed with pimiento) in a jar. Today, even mainstream supermarkets showcase a stunning variety of these little fruits arrayed in olive bars. Most bars don’t provide nutritional information, preventing comparisons among the choices. However, green olives generally contain about double the sodium of black olives.
Given the increased availability of olives, it might be wise to avoid canned black olives, which have been reported to be high in acrylamide; however, most other olives contain no detectable amounts.255 (Olive oil has not been found to contain acrylamide.)
Few foods have been at once as maligned and acclaimed as coconut oil. Because it’s the most concentrated source of saturated fat in the food supply—even higher than lard or butter—some view it as a notorious health villain. Not surprisingly, it rests atop the “avoid” column in the list of mainstream heart-health foods.
Others view coconut oil as a fountain of youth and the greatest health discovery in decades. These advocates claim that coconut oil can provide therapeutic benefits for Alzheimer’s disease, dementia, cancer, diabetes, digestive disturbances, heart disease, high blood pressure, HIV, kidney disease, osteoporosis, overweight, Parkinson’s disease, and many other serious conditions. So what’s the truth?
Based on the available science, coconut oil is neither a menace nor a miracle food. Coconut oil should be regarded like any other oil: a concentrated food that provides a lot of calories with limited nutrients. It certainly provides a vegan option for solid fat when preparing special-occasion treats, but as with other fats and oils, its use should be minimized. On the other hand, whole coconut (at varying stages of maturity) should be treated in much the same way as other high-fat plant foods—enjoyed in moderation, primarily as a whole food. As such, coconut is loaded with fiber, vitamin E, and healthful phytochemicals and has antimicrobial properties.
The relative health effects of coconut oil consumption remain somewhat uncertain. Some people believe that eating coconut oil does no harm because it’s cholesterol-free; others claim it’s harmful because it lacks essential fatty acids. But we can’t ignore the fact that in many parts of the world where coconut and coconut oil are the principal sources of dietary fat, the rates of chronic disease, including CAD, are low.256–258 There’s one major caveat: the benefits seem to apply only when coconut products are consumed as part of a diet rich in high-fiber plant foods and lacking processed foods.
Recall the Marshallese (see pages 56 to 58), who had virtually no diabetes seventy years ago. The traditional Marshallese diet employed a wide variety of coconut products, which furnished an estimated 50 to 60 percent of total calories. When an indigenous diet gives way to a Western-style diet containing processed foods laden with white flour, sugar, and fatty animal products, disease rates escalate even when coconut products continue to be consumed. The Marshallese experience with increased rates of diabetes after such a dietary switch offers confirmation.
The main reason coconut oil is so often blacklisted by health care providers is because approximately 87 percent of its fat is saturated.165 Many people imagine saturated fat as a single tyrant that clogs arteries, but different types of saturated fats exist. Depending on the length of the carbon chain, these fatty acids have very different effects on blood cholesterol levels and on health. Short-chain fatty acids contain 1 to 6 carbon atoms; these fats come largely from bacterial fermentation of indigestible carbohydrates. There’s mounting evidence that short-chain fatty acids are highly beneficial to health, particularly colonic health. Medium-chain fatty acids contain 8 to 12 carbon atoms. These fatty acids have generated a great deal of interest among scientists and consumers, because they’re quickly metabolized and used as energy (relative to longer-chain fatty acids, which are more likely to be stored in adipose tissue). Some evidence suggests that medium-chain fatty acids promote greater total energy expenditure, possibly aiding in weight control.259 Long-chain fatty acids contain 13 to 21 carbon atoms, while very long-chain fatty acids contain 22 or more carbon atoms. Not all authorities agree on the chain length for each category. For example, 6-carbon fatty acids are sometimes considered medium-chain fatty acids, and 12-carbon fatty acids are sometimes classified as long-chain fatty acids.
The saturated fatty acids most abundant in the food supply are lauric acid, myristic acid, palmitic acid, and stearic acid. Their carbon-chain length and main food sources are:
• Lauric acid (12 carbon atoms): coconuts, coconut oil, palm kernel oil
• Myristic acid (14 carbon atoms): dairy products, coconuts, coconut oil, palm oil, palm kernel oil, nutmeg oil
• Palmitic acid (16 carbon atoms): palm oil, animal fats
• Stearic acid (18 carbon atoms): cocoa butter, mutton fat, beef fat, lard, butter
Saturated fatty acids with 12 to 16 carbon atoms increase LDL cholesterol levels, while 18-carbon stearic acid doesn’t.260 However, stearic acid isn’t completely off the hook; some evidence shows high intakes could adversely affect other CVD risk factors, such as lipoprotein(a) and certain clotting factors.180,260
As it happens, approximately 70 percent of the fat in coconut oil comprises saturated fatty acids known to raise blood cholesterol levels: about 45 percent is lauric acid, 17 percent is myristic acid, and 8 percent is palmitic acid. Another 15 percent is 6- to 10-carbon fatty acids, and about 3 percent is stearic acid.165 Case closed?
Well, not exactly. The predominant fatty acid, lauric acid, does raise total cholesterol, but it appears to raise HDL cholesterol to an even greater extent than LDL cholesterol, favorably altering the ratio of HDL to total cholesterol.261,262 In addition, lauric acid is converted in the body into monolaurin, an antiviral, antifungal, and antiseptic compound—and coconut oil is among the richest food sources of lauric acid.263–267 There’s also evidence that coconut products have anti-inflammatory and antioxidant activity. Note that the compounds responsible for these benefits (which include a variety of phytochemicals, such as phenolic acids) are largely eliminated when coconut oil is refined.263,268,269 The conclusion: Coconut products, including mature-coconut meat, young-coconut meat, and coconut water, can be part of a healthy vegan diet. Consumption of coconut oil, like other fats and oils, is best minimized.
Including moderate amounts of high-fat plant foods can make eating more enjoyable and can add immensely to a diet’s nutritional quality. One serving equals 1 ounce of nuts or seeds or half an avocado. For most people, two or three daily servings of such higher-fat plant foods is reasonable, while higher intakes are appropriate for athletes and others with increased caloric requirements.
The use of fats and oils alone is more controversial. At 9 calories per gram—about 120 calories per tablespoon—fats and oils are the most calorically dense foods. However, because they provide few nutrients per calorie, they have the lowest nutrient density of any food. As a result, direct consumption of fats and oils isn’t necessary; nutrient-packed whole foods can provide all the fat needed by most individuals. On the other hand, added fats and oils can have a place in a healthful diet, as they do in the diets of many healthy populations throughout the world. Fats and oils add variety, flavor, and extra calories (without adding bulk) when needed. They also help to improve the absorption of fat-soluble vitamins and protective phytochemicals.
Oil-extraction methods can influence the quality and nutrition of the finished product. Most vegetable oil sold in mainstream grocery stores is refined oil; the solvent extraction process relies on hexane, a petroleum byproduct. The oils then are degummed using acid, neutralized using caustic soda, bleached, deodorized, and dewaxed; the goal is to produce oils that are clear, colorless, and odorless. Finally, preservatives are commonly added to extend their shelf life.
To prevent deterioration of the unsaturated fats in high-fat plant foods, they’re best kept refrigerated or frozen. Most nuts will keep four to six months in their shell at room temperature (although cooler temperatures will extend storage time). If stored in the refrigerator at 32 to 45 degrees F (0 to 7.2 degrees C), nuts and seeds will keep in their shells for a year or longer. Once their protective coating has been removed or is broken, nuts and seeds will keep for three to four months in the refrigerator and up to a year in the freezer. Because walnuts, chia seeds, ground flaxseeds, hempseeds, and wheat germ have higher levels of the more unstable omega-3 fatty acids, they’re best kept frozen.
Oils, particularly the more nutritious expeller-pressed oils, will stay fresher when refrigerated or frozen. Although most oils will keep up to three months or longer in the refrigerator, oils high in omega-3 fatty acids, such as those extracted from flaxseeds and hempseeds, spoil very quickly and should be used within four to six weeks. (For sparing use, keep a small bottle in the refrigerator and freeze the rest.) Olive oil can be stored in a cool, dark place because it’s more stable than most other mechanically pressed oils; however, it’s still a good practice to keep it refrigerated. It becomes semisolid when cold but melts at room temperature.
Expeller pressing is an extraction technique that uses a screw or auger to squeeze oil from nuts, seeds, fruits, grains, or legumes. Although some heat is naturally produced from friction during this process, temperatures generally remain below 200 degrees F (93 degrees C). Some oils are truly cold-pressed, either because the oil is easily extracted and little heat is generated during the process, or because the pressing is conducted under temperature-controlled conditions to keep the materials cold. As a result, more valuable nutrients, antioxidants, phytosterols, and phytochemicals are retained in cold- and expeller-pressed oils than in conventionally refined vegetable oils. Also, the rich colors and flavors of the plants from which they were extracted are preserved, making expeller-pressed or mechanically pressed oils preferable to refined oils.
Virgin and extra-virgin olive oils are expeller pressed; today, they’re widely available in stores. Most other expeller-pressed oils are sold in the supermarket’s natural food section or in a natural food store. Those rich in omega-3 fatty acids are kept refrigerated.270
In any case, consumption of added fats and oils should be moderate. For salads and raw food preparation, oils rich in omega-3s (or with a good balance of essential fatty acids) are an excellent choice. (For more on essential fatty acids, see pages 117 to 134.) It’s best not to expose these oils—especially good-quality unrefined oils—to direct heat, because they have a very low smoke point and are rapidly damaged.
For cooking, refined oils (such as pure olive oil or organic canola oil) are sensible choices, because they can withstand higher temperatures. People often mistakenly assume that coconut oil is the best cooking oil. However, virgin and extra-virgin coconut oils have smoke points closer to 350 degrees F (177 degrees C). Only refined coconut oil has a high smoke point of about 450 degrees F (232 degrees C).271
In general, vegetable margarine is a less healthy choice than refined oil, and its use should be minimized. (The most healthful spreads are nut and seed butters; they provide far greater nutritional value per calorie than any concentrated fats or oils.) Margarine is more highly processed, generally contains undesirable additives, and often is made with cheap oil or oils that are sourced unsustainably. Margarine may also contain trans-fatty acids.
Unfortunately, a claim that a product is free of trans fats is no guarantee that it actually is. A manufacturer can legally state on its nutrition label that a product has no trans-fatty acids if it contains less than 0.5 gram per serving in the United States and less than 0.2 gram per serving in Canada. The best way to be sure a product really is free of trans fats is to read the list of ingredients; if “partially hydrogenated oil” is present, the product contains trans-fatty acids.
