Abstract
PURPOSE: Little is known about the relationship between the human gut microbiota composition and equol-producing ability. The aim of this study is to evaluate the relationship between equol production and the gut microbiota in school-age children, with consideration of sex, age, and exposure to soy isoflavones. METHODS: Participants were 1110 students aged 7-8, 10-11 and 13-14 years. The cumulative participation rate was 85.2%. Equol production, defined as a log-transformed equol/daidzein ratio of -1.75 or greater, was determined in urine collected after two days of soymilk supplementation. Urinary daidzein, genistein, and equol were measured by liquid chromatography-mass spectrometry. The microbiota in 223 fecal samples was determined by 16S rRNA gene sequencing analysis. RESULTS: The observed operational taxonomic unit number, Chao 1, and Shannon index were significantly higher in equol producers than in non-producers after adjustments for survey time, sex, and age. Principal coordinate analysis plots based on weighted and unweighted UniFrac distances showed significant differences in the gut microbiota between equol producers and non-producers. Among the species with an average abundance of ≥0.1%, several species were more abundant in equol producers than in non-producers, with significant positive correlations between relative abundances and equol/daidzein ratios. Of species previously reported as equol-producing, Asaccharobacter celatus and Slackia isoflavoniconvertens were significantly associated with equol production. CONCLUSION: Equol production was strongly associated with the diversity of the gut microbiota. The richness of a diverse microbiota and the interrelationships among microbes may be involved in equol production.