equol

Equol is an isoflavandiol phytoestrogen produced in the human gut as a metabolite of the soy isoflavone daidzein by certain intestinal bacteria. It exists as enantiomers, with the S-enantiomer (S-equol) generally exhibiting greater estrogenic activity than the R-enantiomer.

Natural occurrence and biosynthesis: Following consumption of soy or other daidzein-containing foods, certain gut bacteria metabolize daidzein to equol through a multi-step process. Not all individuals harbor these bacteria, so equol production is not universal. Bacterial taxa implicated in equol formation include Adlercreutzia equolifaciens, Slackia isoflavoniconvertens, and some Eggerthella species.

Biological activity: Equol binds to estrogen receptors, with a preference for ER beta, and may have estrogenic or antiestrogenic effects depending on hormonal context. It is generally more potent than daidzein in receptor binding and related assays.

Health relevance: Some studies associate equol production with benefits such as relief of menopausal symptoms, improved bone density, and favorable cardiovascular markers, but results are inconsistent and causality remains unproven. Effects may depend on diet, microbiome composition, and individual hormone status.

Safety and regulation: Equol is not approved as a drug. It occurs naturally in foods containing daidzein, and equol-containing supplements are marketed in some regions. Safety data are limited, and potential hormone-related risks warrant cautious use in hormone-sensitive conditions.