|Type||Prohibited Foods||Typical Health Practices|
||Varies from group to group. Some use vitamin and mineral products; others do not.|
|Lacto-ovo-vegetarian||Meat, fish, poultry||More likely than omnivores to be physically active and not smoke or use alcohol.|
|Semivegetarian||Meat, but may include small amounts of fish and poultry in the diet||Links to conventional health care system tend to be stronger than those of vegans.|
|Vegan||Meat, fish, poultry, eggs, dairy||Vegans tend to be physically active, avoid drugs and tobacco products,* and rely on unconventional rather than conventional health care. Exceptions include macrobiotics who often smoke cigarettes and Rastafarians who smoke marijuana.|
To be safe from the nutritional standpoint, any eating pattern, vegetarian or not, must provide balance, variety, and moderation. It must meet special nutrient needs that arise during infancy, adolescence, pregnancy, lactation, and other stages of the life cycle. It must accommodate special therapeutic considerations, which individuals with certain health problems require. It should also reduce risks of diet-related diseases.
Benefits and Risks
There is considerable agreement among experts about the dietary patterns that lower chronic disease risks. The American Heart Association, American Cancer Society, National Cholesterol Education Program and Committee on Diet and Health of the National Research Council all recommend that adults reduce fat consumption to 30% of calories, with no more than 10% of calories as saturated fat. Some vegetarians-especially those who eat no animal foods at all-achieve these recommended intakes better than most omnivores [Am J. Clin Nutr. 48:712-738, 1988]. However, vegan diets may fall short in certain nutrients unless they are carefully planned.
Table 2 summarizes some of positive aspects of health status among vegetarians. But ill-planned vegetarian diets pose substantial risks (see Table 3). Problems most commonly occur with vegan diets because vegans eliminate all animal foods and may also avoid foods that are processed or not "organically grown." Vegans often refuse to use supplements and may eschew conventional medical care as well [Am J. Clin Nutr. 48:811-818, 1988].
Table 2. Possible Benefits of Vegetarian Eating
|Leanness||Vegetarians tend to be more physically active than nonvegetarians. Higher intakes of dietary fiber may decrease absorption of food by 2-3 % and contribute to a feeling of fullness.|
|Lower blood pressure||Vegans, who consume a diet very low in fat, tend to have blood pressures 10 to15 mm Hg lower than nonvegetarians of similar age and gender. Much of this effect appears to be related to body weight rather than other dietary variables.|
|Lower serum cholesterol||Total blood cholesterol levels are lower in vegans than in lactovegetarians or nonvegetarians. Whole-fat milk products and eggs tend to raise serum blood lipids due to their saturated fat and cholesterol content. Vegetarians often use non- or lowfat milk, and vegans use no milk or eggs at all|
|Less colon cancer||Diets high in meat may increase the incidence of colon cancer by increasing the fecal concentration of various carcinogens. A high intake of animal fat also may increase the risk of colon cancer. It is also possible that carcinogens are produced by cooking meat at very high temperatures.|
Unless they choose a proper balance of foods, strict vegetarians at risk for several deficiencies, especially vitamin B12. The other nutrients at risk are riboflavin, calcium, iron, and the essential amino acids lysine and methionine. Vegetarian children not exposed to sunlight are at risk for vitamin D deficiency. Zinc deficiency can occur in vegans because the phytic acid in whole grains binds zinc, and there is little zinc in fruits and vegetables. Since B12 is present only in animal foods and a limited number of specially fortified foods, vegans should probably take B12 supplements prescribed by a physician. Table 3 summarizes some of these risks.
Table 3. Possible Risks of Vegetarian Eating
|Osteoporosis||There is little evidence that a vegetarian diet causes or cures osteoporosis. One recent study of 290 postmenopausal women found no differences in the measurements of bone mineralization between nonvegetarians and lacto-ovo-vegetarians.|
|Rickets||Vegan children who have limited sun exposure may be at risk of developing rickets secondary to vitamin D deficiency. One study found very low intakes of calcium and vitamin D among macrobiotic infants. Only one received a daily supplement of vitamin D, and 15 (28%) were found to have rickets. Another study found low serum concentrations of vitamin D among lactating macrobiotic women living in Boston.|
|Iron-deficiency anemia||Low serum ferritin levels (a sensitive measure of iron storage status) were found in 5% of male and 27% of female lacto-ovo-vegetarians, and mean ferritin levels of omnivores were significantly higher than those of vegetarians in one recent study.|
|Macrocytic anemia||Signs of vitamin B12 deficiency have been observed in some breast-fed infants of women who are strict vegetarians.|
|Emaciation or slowed growth||Excessive leanness and/or slow growth are have been noted among vegan and vegetarian infants and young children after weaning.|
Another danger of vegan diets is insufficient energy intake (calories), especially during infancy and early childhood. If energy needs are not met, body proteins will be broken down for energy, and this creates additional problems [Ann Rev Nut 11:61-92, 1991]. Therefore, adequate energy intake should be the foremost consideration in vegan dietary planning.
Low protein digestability and quality are other potential risks. Protein quality depends on both digestibility and amino acid composition. The digestibility of protein in the usual American mixed diet is good, probably 95%to 96%. But plant protein foods high in fiber or other inhibitors may have digestibilities as low as 80% [World Health Organization Technical Report 724, 1985]. The digestibility of vegetable protein in one vegan diet for a child was found to be only 86% [Am J. Clin Nutr. 48:868-874, 1988]. Low protein quality is rarely seen in American vegetarian diets, except among vegans or fruitarians who eat small amounts of a single plant food (such as rice or fruit) as a staple. Single plant protein foods usually are lower in protein quality than most animal proteins because they lack significant amounts of various essential amino acids. Table 4 indicates the limiting amino acids (the essential amino acids present in shortest supply) in foods commonly eaten by vegans and lacto-(ovo)-vegetarians.
|Food Group||Limiting Amino Acids||Combine With||Example|
|Legumes (beans,peas, lentils)||Tryptophan, methionine||Grains, nuts/seeds||
|Grains (wheat, rice, oats, barley, corn, rye)||Lysine, isoleucine, threonine||Legumes, dairy||Kidney beans and rice|
|Nuts/seeds (almond, cashew, filbert, pumpkin, sesame, sunflower, walnut)||Lysine, isoleucine||Legumes||Kidney bean soup with sesame seeds; whole-grain cereal with milk|
|Animal foods||Not as limited||Any of above||Vegetables with yogurt dressing|
Plant foods low in particular amino acids can be combined with other plant or animal foods containing them to provide an mixture containing all of the essential amino acids. These combinations of "complementary" proteins compensate for the limited amounts of amino acids in the proteins of individual plants. Table 4 shows, for example, how legumes (which are low in two essential amino acids) can be combined with grains (which contain ample amounts of these two but are low in three others) to supply a mixture adequate to meet body needs.
It is not necessary to eat complementary proteins at every meal; it suffices to eat them over the course of a day. Both body protein breakdown and amino acids from recently ingested proteins provide a general body pool of amino acids that can temporarily fill any gaps.
To assure adequacy with respect to energy and other nutrients, vegetarians should follow these simple principles:
Vegetarianism based on sound nutrition principles can be a healthful choice, but neither vegetarians nor omnivores have a monopoly on healthful eating. Vegetarians are just as diverse in their health status as are nonvegetarians. Similar health benefits can be gained from both well-selected omnivorous and vegetarian diets.
This article was written in 1991 when Ms. Dingott was a staff nutritionist at New England Memorial Hospital, Stoneham, Massachusetts. Dr. Dwyer is director of the Frances Stern Nutrition Center, New England Medical Center Hospitals, and professor of medicine (nutrition) and community health at Tufts University Medical School. This article, originally published in Nutrition Forum, was prepared with partial support from grants MCJ8241 and MCJ9120 from the MCH Service, U.S. Dept. of Health and Human Services.