Effect of soy and probiotics on fecal microflora and fecal enzyme activity in post-menopausal women with and without a history of breast cancer

The human large intestine hosts a diverse range of bacterial species which play an important role in colonic metabolism and health, and bacterial differences have been implicated in the etiology of disease including cancer. Consumption of probiotics may contribute to the alteration of the intestinal microflora composition. The exact bacterial species responsible remains unknown but it appears their metabolism is important. The metabolism of the dietary soy phytoestrogen daidzein to equol is exclusive of intestinal bacteria. Epidemiological data have shown an inverse association between breast cancer risk and soy phytoestrogen intake as well as increased urinary excretion of equol. The apparent protection might be due to a different plasma hormonal profile in equol producers that is correlated to lowered breast cancer risk. However, phytoestrogen bioavailability and equol production varies greatly between individuals. In this study, a randomized, cross over dietary intervention was undertaken with post menopausal breast cancer survivors (n=20) and control subjects (n=20) at a low risk for developing the disease. Fecal microflora and fecal profiles were determined and compared between groups for the baseline period and after consumption of diets containing soy or milk proteins with or without probiotic supplementation.; At baseline, no statistically significant differences were found between breast cancer survivors and the control group or when stratified based on equol status with respect to bacterial populations, however; women with no cancer history had significantly (P=0.04) higher levels of beta glucuronidase as compared to breast cancer survivors.; When evaluating dietary intervention for all subjects, Bacteroides populations were significantly lower (P=0.02) in the presence of soy. When dividing the group based on cancer status, Bifidobacteria populations were significantly higher in survivors (P=0.04) as compared to controls while on the soy diet. In the presence of probiotics, beta glucuronidase and beta glucosidase were significantly higher in the control group (P=0.02; P=0.03) as compared to breast cancer survivors.; The results of the study suggested that dietary intervention influence the fecal microbial composition and metabolic activities in various population subgroups differently which could play a significant role in health benefits and disease prevention.