Fecal bacterial community changes associated with isoflavone metabolites in postmenopausal women after soy bar consumption

Abstract

Soy isoflavones and their metabolism by intestinal microbiota have gained attention because of potential health benefits, such as the alleviation of estrogen/hormone-related conditions in postmenopausal women, associated with some of these compounds. However, overall changes in gut bacterial community structure and composition in response to addition of soy isoflavones to diets and their association with excreted isoflavone metabolites in postmenopausal women has not been studied. The aim of this study was to determine fecal bacterial community changes in 17 postmenopausal women after a week of diet supplementation with soy bars containing isoflavones, and to determine correlations between microbial community changes and excreted isoflavone metabolites. Using DGGE profiles of PCR amplified 16S rRNA genes (V3 region) to compare microbial communities in fecal samples collected one week before and one week during soy supplementation revealed significant differences (ANOSIM p<0.03) before and after soy supplementation in all subjects. However, between subjects comparisons showed high inter-individual variation that resulted in clustering of profiles by subjects. Urinary excretion of isoflavone (daidzein) metabolites indicated four subjects were equol producers and all subjects produced O-desmethylangolensin (ODMA). Comparison of relative proportions of 16S rRNA genes from 454 pyrosequencing of the last fecal samples of each treatment session revealed significant increases in average proportions of Bifidobacterium after soy consumption, and Bifidobacterium and Eubacterium were significantly greater in equol vs non-S-(-)equol producers. This is the first in vivo study using pyrosequencing to characterize significant differences in fecal community structure and composition in postmenopausal women after a week of soy diet-supplementation, and relate these changes to differences in soy isoflavones and isoflavone metabolites.

Trial registration: Clinicaltrials.gov NCT00244907.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. UPGMA dendrograms of 16S rRNA gene PCR-DGGE profiles of fecal samples collected from postmenopausal women.

(A) Representative examples of within subject comparisons (subject 325). (B) Comparison between all subjects using the last samples from each treatment session. Each profile is labeled by subject number, collection day and soy treatment. Dendrograms were constructed using UPGMA of pairwise Dice similarities comparisons between samples. ‘No-soy’ samples represent the samples before the supplementation with soy and, ‘Soy’ samples refers to samples collected during the week of supplementation with soy.

Figure 2. Principal coordinate analysis (PCoA) of weighted Unifrac distances of subjects (A) before soy consumption and (B) after soy consumption.

Non-S-(-)equol producers are represented by red dots, and blue dots represent S-(-)equol producers.

Figure 3. Canonical correspondence analysis of fecal bacterial composition and alpha diversity measures and postmenopausal women metrics.

Non-S-(-)equol producers are represented by green dots, and red dots represent S-(-)equol producers. Arrows represent the direction of the host factors significantly corresponding to bacterial community composition. Host factors depicted are equol producers, non-S-(-)equol producers, with no soy in diet, after soy intervention, years post-menopause and alpha diversity (illustrated PD whole tree phylogenetic diversity but Chao1 and Shannon have the same trajectory). Variation explained in horizontal axis is 8.2% and the vertical axis is 6.9%.