Calories, fat, fibers, and cellular proliferation in Swiss Webster mice

Increased cellular proliferation has been associated with the enhanced expression of several key stages in carcinogenesis. A standard protocol was used to investigate the effect of specific dietary regimens on cellular proliferation. Young adult Swiss Webster mice were fed for 30 days with modified AIN-76A semi-purified diets designed to illustrate the effects of the levels of dietary or calorie restriction, different fibers and bulking agents, and different fats on cellular proliferation. Female mice were used for the restriction and fat studies, males for the fiber and bulking agent studies. Vaginal smears were taken from females from treatment day 15, and the mice killed 2 days following the first estrus following 30 days feeding; males were killed on the 30th day. One hour before death, mice were injected ip with 0.25 micro Ci/g 3[H]-thymidine. Slides were prepared for radioautography and histopathology. Both dietary and calorie restriction led to reduced 3[H]-thymidine labeling indices in each of the seven tissues studied, the mammary gland being the most severely affected. Different fibers and bulking agents, in specific cases, reduced labeling in the duodenum but not to a consistent statistically significant extent in the colon or colo-rectal region. In the duodenum, oat bran and oat gum were the most effective while wood cellulose (alphacel) had no effect. Investigations on the effects of different fats is continuing. High levels of lard, menhaden oil, or cod liver oil as the fat component of the AIN-76A diet, led to much higher levels of labeled cells in the mammary gland or colo-rectal region than did fat components rich in vegetable oils. The labeling indices appeared to be inversely correlated with the level of linoleic acid in the diet, a presumption that has been confirmed by investigating a series of diets containing different levels of this acid. Anti-oxidants were not used in any of these fat-modified diets. The overall results obtained in these studies clearly indicate the utility of cellular proliferation studies in investigating the effects of dietary modifications.