Soy reduces colon cancer risk in humans and rats

Three studies were conducted to determine (1) the influence of age and history of colonic polyps, cancer or FAP on colonic epithelial cell proliferation indices in humans, (2) the efficacy of soy protein isolate (SPI) supplements to reduce intermediate biomarkers of colon cancer (CC) risk in humans at risk for CC, and (3) the influence of soy products on development of aberrant crypt foci (ACF) and on colonic epithelial cell proliferation in AOM-initiated rats. In the first study, subjects (N = 46) were grouped based on age and clinical history of polyps, FAP and CC. Colon biopsies were obtained by colonoscopy and cell proliferation was measured by proliferating cell nuclear antigen (PCNA) and Ki-67 immunohistochemistry (IHC) and relative PCNA protein levels by slot-blot quantification.; The second experiment was a double-blind, prospective study designed to determine if consumption of one of two supplements containing 38 g/d of SPI with 58 mg of total genistein or 40 g/d of calcium caseinate for one year would influence colonic epithelial cell proliferation as measured by PCNA and Ki-67 labeling and PCNA protein expression in colonic epithelial cells. Colonic biopsies from were obtained from subjects (N = 42; age = 34--70; previous history of adenomatous polyps or CC) before and after supplementation and used for IHC detection of PCNA and Ki-67 antigens in colon crypts and for determination of relative PCNA protein expression by slot-blotting.; The third study investigated the potential of different soy products with varying levels of phytochemicals to reduce aberrant crypt foci (ACF) development and colonic epithelial cell proliferation in carcinogen-initiated rats. The dietary treatments (n = 15 rats/treatment) were full fat soy flakes (SFK), de-fatted soy flour (SFL), soy concentrate (SC), SC plus 150 mg/kg genistein (GEN), and SC plus 5 g/kg calcium (CAL). After 12 weeks of dietary treatment, rats consuming SC had the greatest (P < 0.05) numbers of total ACF, large ACF and total aberrant crypts among all treatment groups. In conclusion, the reductions we observed in colonic epithelial cell proliferation in humans and animals consuming soy in these studies are characteristic of alterations that would be associated with an overall decrease in risk for CC. (Abstract shortened by UMI.)...