DAIRY PROTEINS PROTECT AGAINST DIMETHYLHYDRAZINE-INDUCED INTESTINAL CANCERS IN RATS

The impact of different dietary protein sources (whey, casein, soybean , red meat) on the incidence, burden and mass index of intestinal tumo rs induced by dimethylhydrazine in male Sprague-Dawley rats was assess ed. A purified diet (based on AIN-76A) with a fat concentration of 20 g/100 g and other proteins substituted for casein (20 g/100 g) was use d. Whey and casein diets were more protective against the development of intestinal tumors than were the red meat or soybean diets, as evide nced by a reduced incidence of rats affected (P = 0.15), fewer tumors per treatment group (burden, P < 0.005), and a reduced pooled area of tumors (tumor mass index) that formed (P = 0.39). Intracellular concen tration of glutathione, an antioxidant and anticarcinogenic tripeptide , measured in liver, was greatest in whey protein- and casein-fed rats and lowest in soybean-fed animals (P < 0.001). For-other tissues (spl een, colon, tumor) the differences were not significant, although the whey-fed animals had the highest concentrations of glutathione (P = 0. 8). Whey is a source of precursors (cysteine-rich proteins) for glutat hione synthesis and may be important in providing protection to the ho st by stimulating glutathione synthesis. A positive correlation was ob served between mean fecal fat concentrations for rats in each treatmen t group and large intestinal tumor burden (r(2) = 0.898, P = 0.05). Fe cal fat could be involved in aiding initiation and/or promotion of car cinogenesis. Whatever the mechanism(s), dairy proteins, and whey prote ins in particular, offer considerable protection to the host against d imethylhydrazine-induced tumors relative to the other protein sources examined.