Premenopausal equol excretors show plasma hormone profiles associated withlowered risk of breast cancer

Increased urinary excretion of equol, a metabolite of the isoflavone daidze in. has been associated with a reduced risk of breast cancer. This risk red uction has generally been presumed to be a consequence of increased isoflav one consumption. However, only 30-40% of the population excretes more than trace amounts of equol, regardless of isoflavone intake. Accordingly, we hy pothesized that the observed apparent protective effect of equol is at leas t in part attributable to hormonal differences between equol excretors and non-excretors, and that these differences are largely independent of isofla vone intake. We measured plasma hormone and sex hormone binding globulin (SHBG) concentr ations in 14 normally cycling premenopausal women during each of three diet periods in which they consumed differing isoflavone doses (0.15, 1.0, and 2.0 mg/kg of body weight/day) as a component of soy protein isolate. The pl asma hormone and SHBG concentrations of equol excreters (n = 5) were then c ompared with those of the non-excretors (n = 9), Results showed that even a t the lowest dose, urinary equol excretion values for excreters far exceede d those for non-excretors consuming the highest dose. At all doses, equol e xcreters generally had lower concentrations of estrone, estrone-sulfate, te stosterone, androstenedione, dehydroepiandrosterone (DHEA), DHEA-sulfate, a nd cortisol and higher concentrations of SHBG and midluteal progesterone, a hormonal pattern overall consistent with lowered breast cancer risk. In co nclusion, the association of equol excretion and lowered breast cancer risk may largely reflect the tendency of equol excreters to have more favorable hormonal profiles, as opposed to merely reflecting increased isoflavone in take. Equol may be a marker for the presence of colonic bacterial enzymatic activity that increases fecal steroid excretion. Alternatively, equol itse lf, even with very modest isoflavone intake, may exert beneficial effects o n the regulation of endogenous hormones.