vegetarianism, theory and practice of eating only fruits and vegetables, thus excluding animal flesh, fish, or fowl and often butter, eggs, and milk. In a strict vegetarian, or vegan, diet (i.e., one that excludes all animal products), the nine amino acids that must be supplied by the diet can be obtained by eating foods that include both grains and legumes (e.g., beans or tofu) at any point during the day. Vitamins B₁₂ and D can be obtained through supplements or the addition of a cup of nonfat milk or yogurt to the daily diet. Ovolactovegetarians obtain complete proteins by including milk, cheese, and eggs in their diets.

The basis of the practice of vegetarianism may be religious or ethical, economic, or nutritional, and its followers differ as to strictness of observance. Certain Hindu and Buddhist sects are vegetarian, as are Seventh-day Adventists. As a general movement vegetarianism arose about the middle of the 19th cent.; it made considerable progress in Great Britain and in the United States. In the contemporary United States, vegetarianism has gained acceptance as a practice that lowers one's risk for the "diseases of affluence," e.g., high blood pressure, heart disease, diabetes, and certain cancers.

Theory or practice of eating only plants. The vegetarian diet includes grains, vegetables, fruits, and nuts; it excludes meat, poultry, and fish, but some vegetarians eat dairy products (lactovegetarians), egg products (ovovegetarians), or both (ovolactovegetarians). Those who eat no animal products (including honey) are called vegans. Motivations vary and include ethics (both unwillingness to kill animals and abhorrence of modern methods of raising animals for meat), self-denial or religious taboo, ecology (including concern about the wastefulness and environmental costs of beef farming), and health. Vegetarians point to the many health benefits of their diet, including low rates of heart disease, diabetes, colon cancer, and obesity. While obtaining sufficient protein is seldom a problem in affluent societies, vegetarians must be careful to consume enough iron and, especially for vegans, calcium and vitamins D and B₁₂. The most influential early proponent of vegetarianism was Pythagoras, in the 6th century BC. Many Hindu sects and most Buddhists are vegetarian, and much of the world eats hardly any meat because it is unavailable. The Enlightenment led to a humane concern for animals; in the 19th century Britain became a major centre of vegetarianism, and vegetarian movements soon arose in Germany, the U.S., and other countries.

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