Soybean diet lowers breast tumor incidence in irradiated rats

This paper examines the relationship between feeding a diet rich in protease inhibitors and the reduction of mammary cancer induced by x-irradiation in Sprague-Dawley rats. Of a total of 145 irradiated animals, 44 % of the 45 rats fed a raw soybean diet containing a high concentration of protease inhibitor developed mammary tumors as compared to 74 % of 50 rats fed a casein diet containing no protease in-hibitor. Animals fed Purina rat chow which contain-ed low levels of protease inhibitor exhibited a 70% mammary tumor incidence. No spontaneous neo-plasms were found in any of the non-irradiated animals on the raw soybean diet whereas about 10% of the animals on the protease-free diet developed tumors. Thus, soybeans which are rich in protease in-hibitors reduced the induction of mammary cancer in x-irradiated rats. This work suggests that diets rich in protease inhibitors may contribute to reducing cancer incidence in man