Urinary Estrogen Metabolites During a Randomized Soy Trial

Abstract

One of the hypothesized protective mechanisms of soy against breast cancer involves changes in estrogen metabolism to 2-hydroxy (OH) and 16α-OH estrogens. The current analysis examined the effect of soy foods on the 2:16α-OH E₁ ratio among premenopausal women during a randomized, crossover intervention study; women were stratified by equol producer status, a characteristic thought to enhance the protective effects of soy isoflavones. The study consisted of a high-soy diet with 2 soy food servings/day and a low-soy diet with <3 servings of soy/wk for 6 mo each; estrogen metabolites were measured in 3 overnight urines (baseline and at the end of the low- and high-soy diet) using gas chromatography mass spectrometry for the 82 women who completed the study. Urinary isoflavonoids were assessed by liquid chromatography mass spectrometry. When applying mixed models, the 2:16α-OH E₁ ratio increased (P = 0.05) because of a nonsignificant decrease in 16α-OH E₁ (P = 0.21) at the end of the high-soy diet. Similar nonsignificant increases in the 2:16α-OH E₁ ratio were observed in equol producers (P = 0.13) and nonproducers (P = 0.23). These findings suggest a beneficial influence of soy foods on estrogen metabolism regardless of equol producer status.

ACKNOWLEDGMENTS

This project was funded by grants from the National Cancer Institute (R01 CA 80843 and P30 CA 71789) and from the National Center for Research Resources (S10 RR 020890). Dr. S. Conroy was supported by grant R25 CA 90956. We thank all participants for their dedication and time to be part of this intervention.