Mechanisms of diet and colon carcinogenesis.

There is consistent and strong evidence that a high risk of colorectal cancer is associated with obesity and with a low intake of vegetables, of whole grain cereals and of fish. Many other food groups or nutrients have been associated with this cancer, but the evidence for them is inconsistent and therefore untenable. Vegetables contain a wide range of protective agents that protect against cancer at many other sites as well as the large bowel. The same is true of whole grain cereals; these can also protect against colorectal cancer by mechanisms specific to the large bowel. Fish are rich in n-3 polyunsaturated fatty acids that are thought to protect the colon against malignancy via the prostaglandin pathway. Overweight is the result of an excess of energy intake over energy output, and there is good evidence to suggest that overweight might be a surrogate measure of lack of exercise.