A cross-sectional study of the gut microbiota associated with urinary and serum equol production status in a general population of Japanese men

Equol is a metabolite produced by the gut microbiota from the soy isoflavone daidzein. Previous studies identified bacteria capable of converting daidzein to equol. We investigated whether equol producers among Japanese with a high soy intake contained these bacteria. We also examined differences in equol production status between urine and serum and how the gut microbiota differs between these statuses. To minimize the potential confounding effects of hormonal variability in women, this cross-sectional study analyzed 853 Japanese men. Urinary and serum isoflavones were collected in the morning after fasting and were analyzed using LC-MS/MS. By applying a finite mixture model for each log 10 equol/daidzein ratio, we defined equol producers and non-producers from urine and serum. Among 669 participants with fecal microbial measurements, the 16S rRNA gene was sequenced on a MiSeq System. The cut-off values for the log 10 equol/daidzein ratio were −0.94 for urine and −0.95 for serum. Equol production status in urine and serum matched in 97 %, and equol producers from urine or serum were 42 %. The microbiota was more diverse in producers than in non-producers; the genus Senegalimassilia included strains with high sequence identity (>98 %) to daidzein reductase. The family Oscillospiraceae and class Clostridia also had approximately 46 %–48 % sequence identity. The equol production status of fasting urine and serum almost matched among a general population of Japanese men. Although we did not detect a microbiota with known daidzein reductase in equol producers, several shared similar sequences; these may include equol-producing bacteria that have not yet been identified.