Nutrition and experimental carcinogenesis: a review.

Restriction of the total diet or the number of calories fed to rats and mice inhibits the formation of tumors in several tissues. Unless animals are fed equivalent levels of food, or attain equivalent body weights, it is difficult to assess the significance of the effect of other nutritional modifications on carcinogenesis. The effects of altering the levels of protein or fat are much less than those seen with dietary restriction. Feeding a protein-free diet is tolerated for a limited period and can alter the metabolism of carcinogens. It may thus affect the tumor incidence induced by one-shot carcinogens. Vitamins have specific effects on the activity of certain carcinogens, the fullest information being available for vitamin A, which has been shown to inhibit or enhance carcinogenesis, and vitamin C, which by reducing sodium nitrite, prevents nitrosation of secondary and tertiary amines occurring in acidic conditions of the stomach. Inorganic substances, such as iodine (thyroid) and copper (liver), may affect the tumor incidence in specific tissues. The metabolic activation of carcinogens is modified by enzyme induction and the administration of antioxidants. The relevance of these results to the induction of cancer in humans is briefly discussed.