The Vegetarian Diet
Source: The American Dietetic Association
Scientific data suggest positive relationships between a vegetarian diet and reduced risk for several
chronic degenerative diseases and conditions, including obesity, coronary artery disease,
hypertension, diabetes mellitus, and some types of cancer.
It is the position of The American Dietetic Association (ADA) that appropriately planned vegetarian
diets are healthful, are nutritionally adequate, and provide health benefits in the prevention and
treatment of certain diseases.
The eating patterns of vegetarians vary considerably. The lacto-ovo-vegetarian eating pattern is
based on grains, vegetables, fruits, legumes, seeds, nuts, dairy products, and eggs, and excludes
meat, fish, and fowl. The vegan, or total vegetarian, eating pattern is similar to the
lacto-ovo-vegetarian pattern except for the additional exclusion of eggs, dairy, and other animal
products. Even within these patterns, considerable variation may exist in the extent to which animal
products are avoided. Therefore, individual assessment is required to accurately evaluate the
nutritional quality of a vegetarian's dietary intake.
Studies indicate that vegetarians often have lower morbidity (1) and mortality (2) rates from several
chronic degenerative diseases than do nonvegetarians. Although nondietary factors, including
physical activity and abstinence from smoking and alcohol, may play a role, diet is clearly a
contributing factor. In addition to the health advantages, other considerations that may lead a person to adopt a
vegetarian diet pattern include concern for the environment, ecology, and world hunger issues.
Vegetarians also cite economic reasons, ethical considerations, and religious beliefs as their reasons
for following this type of diet pattern. Consumer demand for vegetarian options has resulted in
increasing numbers of foodservices that offer vegetarian options. Presently, most university
foodservices offer vegetarian options.
Health Implications of Vegetarianism
Vegetarian diets low in fat or saturated fat have been used successfully as part of comprehensive
health programs to reverse severe coronary artery disease (3,4). Vegetarian diets offer disease
protection benefits because of their lower saturated fat, cholesterol, and animal protein content and
often higher concentration of folate (which reduces serum homocysteine levels) (5), antioxidants
such as vitamins C and E, carotenoids, and phytochemicals (6). Not only is mortality from coronary
artery disease lower in vegetarians than in nonvegetarians (7), but vegetarian diets have also been
successful in arresting coronary artery disease (8,9). Total serum cholesterol and low-density
lipoprotein cholesterol levels are usually lower in vegetarians, but high-density lipoprotein cholesterol
and triglyceride levels vary depending on the type of vegetarian diet followed (10).
Vegetarians tend to have a lower incidence of hypertension than nonvegetarians (11). This effect
appears to be independent of both body weight and sodium intake. Type 2 diabetes mellitus is much
less likely to be a cause of death in vegetarians than nonvegetarians, perhaps because of their higher
intake of complex carbohydrates and lower body mass index (12).
Incidence of lung and colorectal cancer is lower in vegetarians than in nonvegetarians (2,13).
Reduced colorectal cancer risk is associated with increased consumption of fiber, vegetables, and
fruit (14,15). The environment of the colon differs notably in vegetarians compared with
nonvegetarians in ways that could favorably affect colon cancer risk (16,17). Lower breast cancer
rates have not been observed in Western vegetarians, but cross-cultural data indicate that breast
cancer rates are lower in populations that consume plant-based diets (18). The lower estrogen
levels in vegetarian women may be protective (19).
A well-planned vegetarian diet may be useful in the prevention and treatment of renal disease.
Studies using human being and animal models suggest that some plant proteins may increase survival
rates and decrease proteinuria, glomerular filtration rate, renal blood flow, and histologic renal
damage compared with a nonvegetarian diet (20,21).
Nutrition Considerations for Vegetarians
Plant sources of protein alone can provide adequate amounts of essential amino acids if a variety of
plant foods are consumed and energy needs are met. Research suggests that complementary
proteins do not need to be consumed at the same time and that consumption of various sources of
amino acids over the course of the day should ensure adequate nitrogen retention and use in healthy
persons (22). Although vegetarian diets are lower in total protein and a vegetarian's protein needs
may be somewhat elevated because of the lower quality of some plant proteins, protein intake in
both lacto-ovo-vegetarians and vegans appears to be adequate (16).
Plant foods contain only nonheme iron, which is more sensitive than heme iron to both inhibitors and
enhancers of iron absorption. Although vegetarian diets are higher in total iron content than
nonvegetarian diets, iron stores are lower in vegetarians because the iron from plant foods is more
poorly absorbed (23). The clinical importance of this, if any, is unclear because iron deficiency
anemia rates are similar in vegetarians and nonvegetarians (23). The higher vitamin C content of
vegetarian diets may improve iron absorption.
Although plant foods can contain vitamin B-12 on their surface from soil residues, this is not a
reliable source of B-12 for vegetarians. Much of the vitamin B-12 present in spirulina, sea
vegetables, tempeh, and miso has been shown to be inactive B-12 analog rather than the active
vitamin. Although dairy products and eggs contain vitamin B-12, research suggests that
lacto-ovo-vegetarians have low blood levels of vitamin B-12. Supplementation or use of fortified
foods is advised for vegetarians who avoid or limit animal foods (24).Because vitamin B-12 requirements are small, and it is both stored and recycled in the body,
symptoms of deficiency may be delayed for years. Absorption of vitamin B-12 becomes less
efficient as the body ages, so supplements may be advised for all older vegetarians. Lacto-ovo-vegetarians have calcium intakes that are comparable to or higher than those of
Calcium intakes of vegans, however, are generally lower than those of both
lacto-ovo-vegetarians and omnivores (26). It should be noted that vegans may have lower calcium
needs than nonvegetarians because diets that are low in total protein and more alkaline have been
shown to have a calcium-sparing effect (27). Furthermore, when a person's diet is low in both
protein and sodium and regular weight-bearing physical activity is engaged in, his or her calcium
requirements may be lower than those of a sedentary person who eats a standard Western diet.
These factors, and genetic influences, may help explain variations in bone health that are independent of calcium intake.
Because calcium requirements of vegans have not been established and inadequate calcium intakes
are linked to risk for osteoporosis in all women, vegans should meet the calcium requirements
established for their age group by the Institute of Medicine (28). Calcium is well absorbed from
many plant foods, and vegan diets can provide adequate calcium if the diet regularly includes foods
rich in calcium (29). In addition, many new vegetarian foods are calcium-fortified. Dietary
supplements are advised for vegans only if they do not meet calcium requirements from food.
Vitamin D is poorly supplied in all diets unless vitamin D-- fortified foods are consumed. Vegan
diets may lack this nutrient because fortified cow's milk is its most common dietary source.
However, vegan foods supplemented with vitamin D, such as soymilk and some cereals, are
available. Furthermore, findings indicate that sunlight exposure is a major factor affecting vitamin D
status and that dietary intake is important only when sun exposure is inadequate (30). Sun exposure
to hands, arms, and face for 5 to 15 minutes per day is believed to be adequate to provide sufficient
amounts of vitamin D (31). People with dark skin or those who live at northern latitudes or in cloudy
or smoggy areas may need increased exposure. Use of sunscreen interferes with vitamin D
synthesis. If sun exposure is inadequate, vitamin D supplements are recommended for vegans. This
is especially true for older persons who synthesize vitamin D less efficiently and who may have less
Studies show zinc intake to be lower or comparable in vegetarians compared with nonvegetarians
(16). Most studies show that zinc levels in hair, serum, and saliva are in the normal range in
vegetarians (32). Compensatory mechanisms may help vegetarians adapt to diets that may be low in
zinc (33). However, because of the low bioavailability of zinc from plant foods and because the
effects of marginal zinc status are poorly understood, vegetarians should strive to meet or exceed the
Recommended Dietary Allowances for zinc.
Diets that do not include fish or eggs lack the long-chain n-3 fatty acid docosahexanoic acid (DHA).
Vegetarians may have lower blood lipid levels of this fatty acid, although not all studies are in
agreement with this finding (34,35). The essential fatty acid linolenic acid can be converted to DHA,
although conversion rates appear to be inefficient and high intakes of linoleic acid interfere with
conversion (36). The implications of low levels of DHA is not clear. However, it is recommended
that vegetarians include good sources of linolenic acid in their diet.
Vegetarianism Throughout the Life Cycle
Well-planned vegan and lacto-ovo-vegetarian diets are appropriate for all stages of the life cycle,
including during pregnancy and lactation. Appropriately planned vegan and lacto-ovo-vegetarian
diets satisfy nutrient needs of infants, children, and adolescents and promote normal growth (37).
Dietary deficiencies are most likely to be observed in populations with very restrictive diets. All
vegan children should have a reliable source of vitamin B-12 and, if sun exposure is limited, vitamin
D supplements or fortified foods should be used. Foods rich in calcium, iron, and zinc should be
emphasized. Frequent meals and snacks and the use of some refined foods and foods higher in fat
can help vegetarian children meet energy needs. Guidelines for iron and vitamin D supplements and
for the introduction of solid foods are the same for vegetarian and nonvegetarian infants. When it is
time for protein-rich foods to be introduced, vegetarian infants can have pureed tofu, cottage
cheese, and legumes (pureed and strained). Breast-fed vegan infants should receive a source of
vitamin B-12 if the mother's diet is not supplemented and a source of vitamin D if sun exposure is
Vegetarian diets are somewhat more common among adolescents with eating disorders than in the
general adolescent population; therefore, dietetics professionals should be aware of young clients
who greatly limit food choices and who exhibit symptoms of eating disorders (38). However, recent
data suggest that adopting a vegetarian diet does not lead to eating disorders (39). With guidance in
meal planning, vegetarian diets are appropriate and healthful choices for adolescents.
Vegetarian diets can also meet the needs of competitive athletes. Protein needs may be elevated
because training increases amino acid metabolism, but vegetarian diets that meet energy needs and
include good sources of protein (eg, soyfoods, legumes) can provide adequate protein without use
of special foods or supplements. For adolescent athletes, special attention should be given to
meeting energy, protein, and iron needs. Amenorrhea may be more common among vegetarian than
nonvegetarian athletes, although not all research supports this finding (40,41). Efforts to maintain
normal menstrual cycles might include increasing energy and fat intake, reducing fiber, and reducing
Lacto-ovo-vegetarian and vegan diets can meet the nutrient and energy needs of pregnant women.
Birth weights of infants born to well nourished vegetarian women have been shown to be similar to
birth-weight norms and to birth weights of infants of nonvegetarians (42). Diets of pregnant and
lactating vegans should be supplemented with 2.0 micrograms and 2.6 micrograms, respectively, of
vitamin B-12 daily and, if sun exposure is limited, with 10 micrograms vitamin D daily (43,44).
Supplements of folate are advised for all pregnant women, although vegetarian women typically have
higher intakes than nonvegetarians.
Meal Planning for Vegetarian Diets
A variety of menu-planning approaches can provide vegetarians with adequate nutrition. Figure 2
suggests one approach. In addition, the following guidelines can help vegetarians plan healthful diets.
Choose a variety of foods, including whole grains, vegetables, fruits, legumes, nuts, seeds and, if
desired, dairy products and eggs. Choose whole, unrefined foods often and minimize intake of highly sweetened, fatty, and heavily
refined foods. Choose a variety of fruits and vegetables. If animal foods such as dairy products and eggs are used, choose lower-fat versions of these
foods. Cheeses and other high-fat dairy foods and eggs should be limited in the diet because of their
saturated fat content and because their frequent use displaces plant foods in some vegetarian diets.
Vegans should include a regular source of vitamin B-12 in their diets along with a source of
vitamin D if sun exposure is limited. Solely breast-fed infants should have supplements of iron after the age of 4 to 6 months and, if
sun exposure is limited, a source of vitamin D. Breast-fed vegan infants should have vitamin B-12
supplements if the mother's diet is not fortified. Do not restrict dietary fat in children younger than 2 years. For older children, include some foods
higher in unsaturated fats (eg, nuts, seeds, nut and seed butters, avocado, and vegetable oils) to help
meet nutrient and energy needs.
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