Do vegetarians get less cancer?

Well, they do have less cancer than omnivores. However, we don't know how much of this difference is due to diet. It's hard to study cancer because it is a disease that can be decades in the making. And, since many lifestyle factors affect risk, it is always difficult to single out the effects of any one of those factors. For example, vegetarians may have reduced mortality risk because they are less obese, exercise more, smoke less and get more medical check-ups.
The lower incidence of smoking is one reason vegetarians have less lung cancer.

In some cases, we have good reason to believe that a vegetarian diet is protective. This is most clear in the case of colon cancer. And, although risk may not be significantly lower for breast and prostate cancer, many studies have found links between animal product intake and risk for these cancers.

Factors in vegetarian diets that appear to be protective against cancer include the following:

Vegetarians eat more fiber.

In fact, vegetarians consume two to three times more fiber than nonvegetarians. The National Cancer Institute (USA) recommends 20 to 35 grams of fiber a day. The average westerner eats just 15 grams a day. Vegetarians typically eat 30 to 45
grams daily.

Vegetarians consume less fat.

Lacto-ovo vegetarians eat diets that are about 10% lower in fat than nonvegetarian diets, and vegan diets are about 20% lower. High fat diets may increase risk for major cancers such as breast, colon, and prostate cancers. There is room for improvement, though, in vegetarian diets. Many vegetarians eat diets that are higher than 30% fat-the upper limit set by the National Cancer Institute. And many experts believe that these limits are still far too high.

Vegetarians don't eat meat.

Red meat in particular can form mutagenic compounds when cooked at high temperatures. Certain groups of people may be at especially high risk if they eat meat because of the way they metabolize these mutagenic compounds.

Vegetarians eat more fruits and vegetables.

Vegetarians consume somewhat more of these foods and may get more of the potential anti-carcinogens in fruits and vegetables. (But everyone, vegetarian or not, needs to eat more of these protective foods.)

Vegetarians consume more phytochemicals.

These are biologically active compounds found only in plant foods, including grains, beans, fruits, vegetables, and nuts. Plants produce them to protect themselves against a host of environmental stressors and they may protect us as well.

Vegetarians have lower body stores of iron.

High iron levels may raise risk for colon cancer, although this is very speculative. The excess iron may generate free radicals-reactive compounds that wreak havoc upon cells.

Vegetarians consume more antioxidants.

These compounds help to neutralize the effects of free radicals. Some are vitamins, such as beta carotene (the vitamin A precursor), vitamin C, and vitamin E, and some are non-vitamin phytochemicals. Vegetarians consume 50% more vitamin C than nonvegetarians and twice as much vitamin E and beta-carotene.