The largest nutritional association, American Dietetic Association, presents a
comprehensive on vegetarianism.
http://www.adajournal.org/article/S0002-8223(97)00314-3/fulltext R. Singh
Refernces have been excluded due to the length of the report.
Position of The American Dietetic Association:Vegetarian Diets
Virginia K. Messina, MPH, RD, Kenneth I. Burke, PhD, RD
Article Outline
• 1. Position Statement
• 1.1. Vegetarianism in Perspective
• 1.2. Health Implications of Vegetarianism
• 1.3. Nutrition Considerations for Vegetarians
• 1.4. Vegetarianism Throughout the Life Cycle
• 1.5. Meal Planning for Vegetarian Diets
• References
• Copyright
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. Vegetarian diets, like all diets, need to be planned
appropriately to be nutritionally adequate.
1. Position Statement
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.
1.1. Vegetarianism in Perspective
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.
1.2. 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).
1.3. 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 nonvegetarians (25), (26). 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 sun exposure.
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.
presents food sources of nutrients that are often of concern for vegetarians.
1.4. 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 inadequate.
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 strenuous
training.
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 (ig and 2.6 ug, respectively, of vitamin B-12 daily and,
if sun exposure is limited, with 10 (ig vitamin D daily (43), (44). Supplements
of folate are advised for all pregnant women, although vegetarian women
typically have higher intakes than nonvegetarians.
1.5. 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.
View Large Image
Download to PowerPoint
FIG 2. Pyramid approach to vegetarian menu planning.
■ 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.
■ ADA Position adopted by the House of Delegates on October 18, 1987, and
reaffirmed on September 12, 1992, and September 6, 1996. This position will be
in effect until December 31, 2001. ADA authorizes republication of the position
statement/ support paper, in its entirety, provided full and proper credit is
given. Requests to use portions of the position must be directed to ADA
Headquarters at 800/877-1600, ext 4896, or hod@eatright.org
■ Recognition is given to the following for their contributions:
Authors: Virginia K. Messina, MPH, RD, and Kenneth I. Burke, PhD, RD
Reviewers:
Winston J. Craig, PhD, RD; Johanna Dwyer, DSc, RD; Suzanne Havala, MS, RD, FADA;
D. Enette Larson, MS, RD; A. Reed Mangels, PhD, RD, FADA; Vegetarian Nutrition
dietetic practice group (Lenore Hodges, PhD, RD; Cyndi Reeser, MPH, RD)
No comments:
Post a Comment