Epidemiological studies have suggested a relationship between diet and
colon cancer incidence. Results from animal studies suggest that
whey protein, but not
casein protein, may provide protective effects against experimentally induced
breast cancer in animals. In the current study, we investigated the effects of
casein and whey diets on chemically induced
colon cancer in male rats. Pregnant female Sprague Dawley rats (days 3-4 of gestation) were maintained on modified AIN-93G diets formulated with a single
protein source of either
casein or whey. Life-time exposure to these diets was studied in the F1 generation (experiment A) or the F2 generation (experiment B). Male offspring were weaned to the same diets as the dams and were maintained on these diets throughout the study. At age 90 days, all rats received
azoxymethane once a week for 2 weeks (s.c., 15 mg/kg). Forty weeks after the last
azoxymethane injection, all rats were euthanized, the colon was examined visually for
tumors, and each
tumor was histologically evaluated. The weights and distribution of all of the
tumors were recorded. In experiment A, rats fed the
casein diet had a 56% incidence of colon
tumors compared with 30% of the rats on whey-based diets (P < 0.05). In experiment B, rats fed the
casein diet had 50% incidence of colon
tumors compared with 29% in the whey group (P < 0.05). There were no significant effects of diet on
tumor multiplicity or mass. These results suggest that consumption of
whey protein-containing diets may reduce the risk of developing colon
tumors.