Obesity can be a considerable health concern for peri- and post-menopausal women. Evidence suggests an association between the gut microbiome and obesity. The study objective was to evaluate the association between being overweight or obese and phenotypic markers of having an overall gut microbial environment not capable of metabolizing the isoflavone daidzein to equol or O-desmethylangolensin (ODMA).

Cross-sectional study of 137 peri- and 218 post-menopausal women, aged 44–55 years, who consumed at least three servings per week of soy (source of daidzein). Equol and ODMA producers and non-producers were identified based on urinary concentrations of daidzein, equol and ODMA in a 24-h urine sample.

Mean body mass index (BMI) and odds of obesity.

Fifty-one women were ODMA non-producers and 226 were equol non-producers. The ODMA non-producer phenotype was positively associated with obesity (OR: 3.33, 95% CI: 1.53, 7.23), and mean BMI was significantly higher in non-producers (28.9 kg/m²) than in producers (26.7 kg/m²), after adjusting for age, ethnicity, and menopausal status. Positive associations with being obese were observed in both peri-menopausal (OR = 3.92, 95% CI: 0.90, 17.0) and post-menopausal (OR = 3.00, 95% CI: 1.22, 7.70) women. The equol non-producer phenotype was not associated with obesity (OR = 1.13, 95% CI: 0.64, 1.98), and mean BMI was not significantly different between equol producers (27.3 kg/m²) and non-producers (26.5 kg/m²).

These results suggest that the ODMA non-producer phenotype is associated with obesity in peri- and post-menopausal women. Further work is needed to confirm these observations in additional populations and to evaluate possible mechanisms.