Diet is a double edged sword. Improper diet increases the risk of cancer but a proper, well balanced diet reduces the cancer risk.

Diet is one of the most important lifestyle factors and has been estimated to account for up to 80% of cancers of the large bowel, breast, and prostate. Diet affects the risk of many other cancers, including cancers of the lung, prostate, stomach, esophagus and pancreas.

Prostate Cancer:

High consumption of meat, especially red meat, substantially increases the risk of prostate cancer.

Vegetables, especially cooked tomatoes, reduce the risk of prostate cancer. In one clinical trial, the role of Vitamin E as a prostate cancer reducing factor was established. In this study there was a 32% decrease in prostate cancer incidence and 41% decrease in prostate cancer mortality in people receiving Vitamin E supplements when compared to controls.

Breast Cancer:

In Japan, people consume Tofu, a soya product. It contains isoflavones that moderate the estrogen receptors in the body such as breast tissue. The incidence of breast cancer is low in Japan when compared to Western women; only 1/4th of the mortality rate of Western women. Japanese women's low fat diet, high fish consumption and drinking green tea also decrease their breast cancer risk.

One case control study found that regular consumption of soy foods was associated with a marked decrease in breast cancer risk in premenopausal women. No effect in post-menopausal women.

A Japanese case-control study also found that tofu intake (3 times/wk compared with less than 3 times/wk) was associated with decreased risk of breast cancer in premenopausal women. Again, soy intake was not protective against post-menopausal breast cancer.

In one study conducted in America, the relation between soy intake and breast cancer risk found that tofu consumption was protective in both premenopausal and post menopausal Asian women.

Lung Cancer:

Lung cancer risk is substantially decreased by a variety of carotenoids. Carotenoids act as antioxidants and thus minimize cell damage.

One study in Boston focused on the effect of different types of carotenoids on lung cancer risk. It was observed that lung cancer risk was significantly lower in subjects who consumed a diet high in a variety of carotenoids. This was especially true with non-smokers who had 63% less risk.

One study conducted in Hawaii reported further evidence for a protective effect from certain carotenoids against lung cancer and that greater protection was afforded by consuming a variety of vegetables compared to only foods rich in a particular carotenoid.

Stomach Cancer:

Nitrates in food and other preservatives added to food including meat are converted into 'nitrites' in the human stomach. The nitrites undergo nitrosation to form 'nitrosamines' and 'nitrosamides'. This increases the risk of stomach cancer in people eating vegetables from nitrate rich soil.

In one study, Vitamin C appeared to protect against the risk of stomach cancer by inhibiting formation of nitrates in stomach.

Cancer of the stomach is 5 times more common in Japanese people compared to Western populations. When Japanese people migrated to the United States, they progressively acquired the low incidence of the US due to changes in their diets.

In one study conducted in Hawaii that involved both Japanese and Caucasians, the stomach cancer risk was associated with consumption of rice, pickled vegetables, and dried/salted fish, and a negative association with vitamin C intake.

One ecological study in Belgium showed a relation between the nitrate and salt consumption and stomach cancer. The analysis of this model showed that the significance of nitrate as a risk factor for stomach cancer mortality increased markedly with higher sodium levels.

Dietary habits and stomach cancer risk was studied in Shanghai, China. According to this study, risks of stomach cancer were inversely associated with high consumption of several food groups, including fresh vegetables and fruits, poultry, eggs, plant oil, and some nutrients such as protein, fat, fiber, tea and antioxidant vitamins.

By contrast, risks increased with increasing consumption of dietary carbohydrates, frequent consumption of preserved, salty or fried foods and hot soup/porridge, with irregular meals, speed eating and binge eating. This provides evidence that diet plays a major role in stomach cancer risk.

No single food can completely prevent cancer but a balanced combination of different groups can help. Appropriate diet can prevent 3-4 million cancers each year.