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Perceiving plant foods as beneficial because they are high in dietary fiber and, generally, lower in saturated fat than animal foods, many people turn to vegetarian diets.
Grain products, for instance, form the base of the U.S. Department of Agriculture and Department of Health and Human Services' Food Guide Pyramid, which recommends 6 to 11 daily servings of bread, cereal, rice, and pasta. Daily intakes advised for other foods are: 3 to 5 servings of vegetables; 2 to 4 servings of fruits; 2 to 3 servings of milk, yogurt and cheese; and 2 to 3 servings of meat, poultry, fish, dry beans, eggs, and nuts. The guide advises using fats, oils and sweets sparingly.
And, who hasn't seen signs in their grocer's produce section urging consumers to eat "5 a day for better health"? This slogan reflects a major government-industry campaign to help people eat more fruits and vegetables as part of a high-fiber, low-fat diet that emphasizes variety.
The campaign is consistent with the USDA-DHHS Dietary Guidelines for Americans, which states, "Most Americans of all ages eat fewer than the recommended number of servings of grain products, vegetables, and fruits, even though consumption of these foods is associated with a substantially lower risk for many chronic diseases, including certain types of cancer" Also noted: "Most vegetarians eat milk products and eggs, and as a group, these lacto-ovo-vegetarians enjoy excellent health."
But health benefits are not the only reason vegetarian diets attract followers.
Certain people, such as Seventh-day Adventists, choose a vegetarian diet because of religious beliefs. Others give up meat because they feel eating animals is unethical. Some believe it's a better use of the Earth's resources to eat low on the food chain--that is, to eat plant foods, rather than the animals that eat the plant foods. And many people eat plant foods simply because they are less expensive than animal foods.
It's wise to take precautions, however, when adopting a diet that entirely excludes animal flesh and dairy products, called a vegan diet. (See "Vegetarian Varieties.")
"The more you restrict your diet, the more difficult it is to get the nutrients you need," says John Vanderveen, Ph.D., director of the Food and Drug Administration's Office of Plant and Dairy Foods and Beverages. "To be healthful, vegetarian diets require very careful, proper planning. Nutrition counseling can help you get started on a diet that is nutritionally adequate."
If appropriately planned, vegan diets, though restrictive, can provide adequate nutrition even for children, according to the American Dietetic Association and the Institute of Food Technologists.
Plant Food Benefits
Registered dietitian Johanna Dwyer, of Tufts University Medical School and the New England Medical Center Hospital, Boston, summarizes these plant food benefits:
"Data are strong that vegetarians are at lesser risk for obesity, atonic [reduced muscle tone] constipation, lung cancer, and alcoholism. Evidence is good that risks for hypertension, coronary artery disease, type II diabetes, and gallstones are lower. Data are only fair to poor that risks of breast cancer, diverticular disease of the colon, colonic cancer, calcium kidney stones, osteoporosis, dental erosion, and dental caries are lower among vegetarians."
According to Dwyer, vegetarians' longevity is similar to or greater than that of non-vegetarians, but is influenced in Western countries by vegetarians' "adoption of many healthy lifestyle habits in addition to diet, such as not smoking, abstinence or moderation in the use of alcohol, being physically active, resting adequately, seeking ongoing health surveillance, and seeking guidance when health problems arise."
Can Veggies Prevent Cancer?
The National Cancer Institute, in its booklet Diet, Nutrition, & Cancer Prevention: A Guide to Food Choices, states that 35 percent of cancer deaths may be related to diet. The booklet states:
FDA, in fact, authorized several health claims on food labels relating low-fat diets high in some plant-derived foods with a possibly reduced risk of cancer.
While FDA acknowledges that high intakes of fruits and vegetables rich in beta-carotene or vitamin C have been associated with reduced cancer risk, it believes the data are not sufficiently convincing that either nutrient by itself is responsible for the association. Nevertheless, since most fruits and vegetables are low-fat foods and may contain vitamin A (as beta-carotene) and vitamin C, the agency authorized a health claim relating diets low in fat and rich in these foods to a possibly reduced risk of some cancers.
Another claim may relate low-fat diets high in fiber-containing vegetables, fruits and grains to a possible reduction in cancer risk. (The National Cancer Institute recommends 20 to 30 grams of fiber a day.) Although the exact role of total dietary fiber, fiber components, and other nutrients and substances in these foods is not fully understood, many studies have shown such diets to be associated with reduced risk of some cancers.
Lowering Heart Disease Risk
FDA also notes that diets high in saturated fats and cholesterol increase blood levels of total cholesterol and LDL cholesterol, and thus the risk for coronary heart disease. (The National Cholesterol Education Program recommends a diet with no more than 30 percent fat, of which no more than 10 percent comes from saturated fat.) For this reason, the agency authorized a health claim relating diets low in saturated fat and cholesterol to a possibly reduced risk of coronary heart disease.
Another claim may relate diets low in fat and high in fruits, vegetables, and grain products that contain fiber, particularly soluble fiber, to a possibly reduced risk of coronary heart disease. However, the agency recognizes that it is impossible to adequately distinguish the effects of fiber, including soluble fiber, from those of other food components.
With respect to increasing fiber in the diet, Joanne Slavin, Ph.D., R.D., of the University of Minnesota, in 1990 in Nutrition Today, gives this advice: "The current interest in dietary fiber has allowed recommendations for fiber supplementation to outdistance the scientific research base. Until we have a better understanding of how fiber works its magic, we should recommend to American consumers only a gradual increase in dietary fiber from a variety of sources."
The American Dietetic Association's position paper on vegetarian diets states, "Because vegan diets tend to be high in bulk, care should be taken to ensure that caloric intakes are sufficient to meet energy needs, particularly in infancy and during weaning." Dwyer and Suzanne Havala, also a registered dietitian, updated the paper in the 1993 issue of the association's journal.
It's generally agreed that to avoid intestinal discomfort from increased bulk, a person shouldn't switch to foods with large amounts of fiber all at once. A sensible approach is to slowly increase consumption of grains, legumes, seeds, and nuts. "Some may choose to eliminate red meat but continue to eat fish and poultry occasionally, and such a diet is also to be encouraged," Jack Zeev Yetiv, M.D., Ph.D., in his book Popular Nutritional Practices: A Scientific Appraisal.
As with any diet, it's important for the vegetarian diet to include many different foods, since no one food contains all the nutrients required for good health. "The wider the variety, the greater the chance of getting the nutrients you need," says FDA's Vanderveen.
In its position paper on vegetarian diets, the American Dietetic Association states that, with a plant-based daily diet, eating a variety of foods and sufficient calories for energy needs will help ensure adequate intakes of calcium, iron and zinc. (See "Replacing Animal Sources of Nutrients.")
The mixture of proteins from grains, legumes, seeds, nuts, and vegetables provides a complement of amino acids so that deficits in one food are made up by another. Not all types of plant foods need to be eaten at the same meal, since the amino acids are combined in the body's protein pool.
"Soy protein," the paper states, "has been shown to be nutritionally equivalent in protein value to proteins of animal origin and, thus, can serve as the sole source of protein intake if desired."
The Institute of Food Technologists also recommends careful diet planning for vegetarians. This is especially important when the diet excludes dairy foods, to ensure adequate intake of calcium, iron, riboflavin, and vitamin D. For these vegetarians, the institute recommends calcium supplements during pregnancy, when breast-feeding, and for infants and children.
The institute and the American Dietetic Association say a vitamin D supplement may be needed if sunlight exposure is limited. (Sunlight activates a substance in the skin and converts it into vitamin D.)
They also point out that vegan diets should include a reliable source of vitamin B12 (see "Replacing Animal Sources of Nutrients"), because this nutrient occurs only in animal foods. Vitamin B12 deficiency can result in irreversible nerve deterioration.
The need for vitamin B12 increases during pregnancy, breast-feeding, and periods of growth, Dwyer says. In a recent issue of Annual Review of Public Health, she writes that elderly people also should be especially cautious about adopting vegetarian diets because their bodies may absorb vitamin B12 poorly.
Unless advised otherwise by a doctor, those taking dietary supplements should limit the dose to 100 percent of the U.S. Recommended Daily Allowances.
With the array of fruits, vegetables, grains, and spices available in U.S. grocery stores and the availability of vegetarian cookbooks, it's easy to devise tasty vegetarian dishes that even non-vegetarians can enjoy.
However, the key to any healthful diet--vegetarian or non-vegetarian--is adherence to sound nutrition principles.
Vegetarians who eat no animal products need to be more aware of nutrient sources. Nutrients most likely to be lacking and some non-animal sources are:
The American Dietetic Association describes three types of vegetarians. They are listed here by the extent to which the diet includes animal foods:
Publication No. (FDA) 96-2296