Dietary soy supplementation and phytoestrogen levels

Objective: To investigate the relationship between levels of phytoestrogens in blood and urine and symptom control in postmenopausal women whose diets were supplemented with soy containing high levels of phytoestrogen. Methods: Phytoestrogen levels in blood and urine were correlated with the number of hot flushes and vaginal maturation indices in 104 postmenopausal women whose diets were supplemented with 60 g of soy powder daily for 3 months in a double-masked, parallel, placebo-controlled trial. The effect of soy supplementation on menopausal symptoms in this study population was reported previously. Results: Serum levels of genistin, daidzin, and equol were significantly higher in women after soy diet supplementation (+756%, +593%, +1008%, and 57% respectively). The concentration of enterolactone in the soy group was increased by 57% compared with baseline, but the difference with placebo was not statistically significant. The increase in phytoestrogen levels in the soy group in blood or urine did not correlate with fewer hot flushes. Vaginal maturation indices did not change in the soy group. Conclusion: Phytoestrogen levels increased in women who consumed soy supplement, but that does not fully explain climacteric symptom reduction. It is possible that other types of yet unknown phytoestrogens or components in soy other than phytoestrogen influence hot flushes. (C) 1999 by The American College of Obstetricians and Gynecologists.