The Effect of Soy Supplementation on Human Gut Microflora Community in Post‐Menopausal Women

Abstract

Soy isoflavones and their metabolites can mimic estrogen and thus, may carry health benefits for postmenopausal women as alternatives to hormone replacement therapy. Equol, a metabolite of daidzein, is suggested to be more beneficial, but to date, the bacteria responsible for this conversion have not been identified conclusively. This research was aimed at characterizing changes in the gastrointestinal microflora of post‐menopausal women with the addition of a soy bar to their diet and therein to identify organisms that might be responsible for equol production. Bacterial DNA was extracted from fecal samples collected from 6 women for 14 consecutive days, with women consuming one soy bar/d (160 mg of isoflavones) from day 8–11. Fingerprints of 16S rRNA of the microbial community for the 14‐day study period were generated using PCR‐DGGE. Results indicated that all subjects had stable microbial fingerprint profiles and there appeared to be no clear effect of soy. In contrast, analyses based on bifidobacterial‐specific primers indicated an increase in Bifidobacteria as a function of soy, in most subjects. Also, equol producers had a more diverse bifidobacterial community, even in the absence of soy. Future work will focus on characterizing members of the bifidiobacterial community qualitatively and quantitatively, and determine for the presence of organisms that have been associated with equol production.