Dietary effects on chemical carcinogenesis in animal models for colon and liver tumors.

Studies of dietary effects on chemical carcinogenesis in rats have demonstrated that colon tumor induction is enhanced by increased dietary fat intake or dietary deficiency of vitamin A in some but not all cases. The enhancing effect of a high-fat diet is augmented by lipotrope deficiency. Induction of hepatic tumors by several different carcinogens also is enhanced in rats fed a high-fat diet marginally deficient in lipotropes. The dietary effects may be exerted through alteration of metabolism of carcinogens, which has been demonstrated in lipotrope-deficient rats, through immunological mechanisms, which influence induction of colon tumors, or through effects on gastrointestinal bacteria and bile acid metabolism. Demonstration of dietary effects on carcinogenesis may require utilization of combined dietary stresses that alter metabolic loads but do not seriously impair growth.