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 B. 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.