Although there is some correlation, case control and cohort epidemiological studies show conflicting results. Low fat diets may render some protection through anticarcinogens found in vegetables, fruits, legumes, nuts, and grains. Substances found in these foods that may be protective include phenols, sulfur-containing compounds, flavones and fibres. It is well known that dietary fibres appear protective against colonic polyps and cancer of the colon. The mechanisms involved are complex and speculative. They involved binding of oxidized bile acids, a decrease in bowel transit time, and generation of soluble fibre products, such as butyrate with differentiating properties. High fibre diets may also protect against breast and prostate cancer by absorbing and inactivating dietary oestrogenic and androgenic cancer promoters. Protective effects of fibre have not been proven in a prospective clinical trial.

It must be stressed that scientific evidence does not currently establish the anticarcinogenic value of vitamin, mineral, or nutritional supplements in amounts greater than that provided by a balanced diet.

A simple way to decrease dietary fat and increase fibre is to consume at least 5 to 9 servings of fruits and vegetables a day. Such a diet may lower a risk of cardiovascular disease as well as cancer.