What is a vegetarian diet?

Even with vegetarianism's various degrees of strictness, the core diet is simply abstention from meat. But that one decision -- the decision not to eat meat -- can have a lot behind it. Vegetarians choose their diet for many reasons. Some are health-conscious, some believe animal agriculture hurts the environment and others have moral or religious objections to meat.

Health

Vegetarianism has become a popular health diet. Vegetarian favorites like fruit, vegetables, whole grains, and legumes are low in fat and cholesterol and rich in fiber, vitamins C and E, potassium, folate and magnesium. The American Dietetic Association even reports that vegetarians have lower blood pressure, cholesterol and body mass indexes than non-vegetarians [source: ADA]. Of course, no diet is automatically healthy. Vegetarians must make sure they take in enough protein, calcium and vitamin B12 without overindulging in fatty, high-calorie foods like cheese.

Environment

Many vegetarians are as concerned with the Earth's well-being as they are with their own. Some vegetarians choose the diet for environmental reasons because they believe traditional agriculture has less of an ecological impact than animal agriculture. Learn more about this unquestionably modern reason for vegetarianism in How Vegans Work.

Moral and Religious

People usually try not to think about where their meat comes from. It can be unpleasant to imagine your hamburger as a wide-eyed cow in the pasture, let alone as an unhealthy animal in a cramped factory farm. But for many vegetarians, disassociation or denial is impossible. They often feel morally unable to eat animals slaughtered for their meat. Vegans take their ethical objections a step further and refuse to eat dairy or eggs from animals that they believe have led unnaturally short and unhappy lives.

Some of vegetarianism's ethical concerns have spread to the mainstream. Even steadfast meat-eaters often like the idea of free-range chicken or cage-free eggs -- animal husbandry techniques that promise a more compassionate alternative to traditional factory farming.

Vegetarians have long chosen the diet for ethical reasons. Although the first practitioners only temporarily avoided meat for purification, the first regular vegetarians began the diet after philosophical awakenings in the Eastern Mediterranean region and India.

The philosopher Pythagoras of Samos (c. 530 BC) taught vegetarianism to his followers. Pythagoras believed that because we are related to animals, we should treat them with kindness. Many other famous philosophers agreed -- Plato, Epicurus and Plutarch condemned animal sacrifice and avoided eating meat.

In India, the Buddhist and Jainist religions teach that humans should not kill sentient creatures for food. Although Buddhism later declined in India, vegetarianism spread to Brahmanism and Hinduism. Many upper castes and some lower castes adopted the Jainist virtue of "ahimsa," or harmlessness, which forbade hurting living things [source: Encyclopaedia Britannica].

But how did vegetarianism transform into a health movement in the 19th century and an animal rights issue in the 20th? In the next section, we'll learn about modern vegetarianism.

Today vegetarianism is trendy -- 25 percent of adolescents even think it's "cool" [source: Time]. The success of vegetarian cosmetics and vegetarian foods like veggie dogs and tofurkey is a testament to the diet's popularity. Groups that promote vegetarianism and animal rights, like the Humane Society of the United States (HSUS) and People for the Ethical Treatment of Animals (PETA), have tremendous lobbying power with major companies. But vegetarianism hasn't always been so generally accepted, nor has it always been linked with the animal-rights movement.

In 17th- and 18th-century Europe, some Protestant groups embraced vegetarianism as a moral directive -- a way to be sinless. By the 19th century, European and North American vegetarianism had become a fringe health movement. Adherents promoted the dietary benefits of vegetarianism -- even coupling it with temperance and anti-tobacco movements. Modern organized vegetarianism began with the formation of the Vegetarian Society in 1847 by the Bible Christian Sect of England. Within a year, the Society had 478 members.

It wasn't until the mid 20th century that vegetarianism partnered with animal rights movement. America's most notorious animal rights organization, PETA, vigorously protests against all meat, animal products and animal testing. It is best known for its bold ad campaigns. The HSUS takes a less strict approach. It accepts that people will eat meat and focus instead on reducing meat consumption, replacing animal products and improving farming techniques. Both PETA and the HSUS, however, are powerful political machines: They hold stock in companies like Tyson, Wal-Mart, McDonald's and Smithfield's.

Check out the links on the next page for more information about vegetarianism.