Vegetarianism pursued for reasons of physical health is a recent practice. It is now regarded as a healthful dietary alternative, thanks to modern nutritional science. Vegetarian diets contain less fat, cholesterol and protein, and more complex carbohydrates and fiber. Such diets appear to provide adequate protein, vitamins and minerals for meeting human physiological requirements, except in growing children and lactating women, for whom it is necessary to supplement iron, vitamin B12 and vitamin D.A vegetarian diet reduces overall mortality, especially from cardiovascular diseases and cancer. It lowers serum cholesterol and low density lipoprotein levels and hence reduces atherosclerosis. It lowers blood pressure and reduces the risk of diabetes. Dietary fibers improve sensitivity to insulin. Vegetarians have been found to have less gastrointestinal cancer, gallstones, diverticular diseases, constipation and even a lower appendicitis rate. Avegetarian diet decreases the likelihood of chronic diseases and, consequently, medical costs.

Although vegetarianism has been practiced for a long time, before the nineteenth century the avoidance of animal food was justified only by moral and metaphysical arguments. However, in the twentieth century an increasing desire for improved health combined with a greater respect for science have helped promote the physiological arguments for vegetarianism. It is now regarded as a healthful dietary alternative, thanks to modern nutritional science. The health benefits of vegetarian diets have been studied extensively, and it appears that almost all organ systems are affected in one way or another.

According to most studies, vegetarians are classified into three groups: those who eat no food of animal origin (except perhaps honey), those who eat dairy products, and those who eat both dairy products and eggs. Most vegetarians also eliminate or reduce their intake of alcohol, tobacco and caffeine. All these dietary habits, together with increased physical activity, are known as the vegetarian lifestyle.

Vegetarian diets contain less fat and protein, but more complex carbohydrates. They are also comparatively low in total cholesterol and saturated fat.

The traditional concern about vegetarian diets has been whether or not they contain enough protein. On a worldwide basis, plant protein contributes sixty-five percent of the per capita supply of protein. Although certain essential amino acids are distinctly lower in certain plant foods than in animal foods, the proteins in certain common plant foods are easier to digest. A mixture of plant proteins can serve as a complete and well-balanced source of amino acids for meeting human requirements. In most studies of vegetarians, no apparent protein deficiencies have been found.

However, the intake of vitamins B12 and D tends to be lower among vegetarians, while mineral intake appears adequate with the exception of iron, zinc and calcium. For lactating mothers or growing infants on a strict vegetarian diet, it is necessary to supplement vitamin B12, vitamin D, calcium and riboflavin. The addition of milk products or eggs to their diets will avoid this problem.

Vegetarian diets have been shown to have good effects against heart disease. Previous studies reported lower mortality in vegetarians, but they used subjects who were religious group members who tended to be thinner and smoke and drink less. A study of the mortality patterns of German vegetarians, after eleven years of follow-up, revealed that the death rate from all causes was reduced by one half compared with the general population. The mortality for heart diseases was reduced to one third of that expected, and cancer mortality was reduced by one half.

Furthermore, a large-scale dietary study indeed suggests that frequent consumption of nuts may protect against heart attacks. Lower blood pressure and a lower rate of hypertension have been especially demonstrated in studies of religious vegetarians, such as Seventh-Day Adventists.

Dietary fiber delays stomach emptying, decreases gastrointestinal transit time, increases stool frequency and the stools become softer. Vegetarians were found to have a lower incidence of gastrointestinal cancer, gallstones, diverticular diseases and constipation. Studies show that meat eaters develop gall stones two and a half times as often as vegetarians and require twice as many emergency appendectomies.