Feeding soybean resistant protein to rats raises fecal bile acid excretionbut counteracts a deoxycholate-caused decrease in colonic aberrant crypt foci

A high-molecular-weight fraction after removal of water-soluble peptides fr om proteinase-treated soybean protein isolate (referred to as HMF) was exam ined for its effect on preneoplastic lesions in the rat colon. For this pur pose, male Fisher-344 rats 7 wk old were divided into 8 groups (n = 5), of which 6 groups received 3 injections of azoxymethane (AOM, 15 mg/kg of body weight) for 3 wk once a week, while all were fed HMF or casein diets suppl emented with or without deoxycholic acid (DCA) over a period of 4 wk. Two g roups of AOM-treated rats were allowed free access to HMF or casein diets w ithout supplemental DCA, respectively, while the others were pair-fed so as to be well matched in their food intake. There were no significant differe nces in growth parameters among the pair-fed groups. Feeding HMF diets rais ed fecal lipid and acidic steroid excretions to a greater extent than feedi ng casein diets, secondary bile acids being conspicuous among acidic steroi ds in the excreta irrespective of the presence or absence of DCA supplement ation. As a result of observation for colonic aberrant crypt foci (ACF), th e intake of HMF proved to reverse the reduction of ACF appearance by DCA. T his result implies that secondary bile acids are caught and brought out by HMF, or rather its derivative "resistant protein," so as not to keep contac t with colonic mucosae.