Faculty Bibliography

BACKGROUND: Soy isoflavones may lower breast cancer risk through altered hepatic estrogen metabolism, leading to increased urinary excretion ratios of 2-hydroxyestrone (20HE1) to 16a-hydroxyestrone (16alphaOHE1). MATERIALS AND METHODS: Urinary excretion of 20HE1/16alphaOHE1 was measured in 36 healthy, pre-menstrual women before and after ingestion of a soy-protein formula containing 120 mg of isoflavone daily for one month. Since isoflavone absorption and metabolism depends on intestinal bacteria, effects of co-administration of Lactobacillus GG (2 x 10(12)) on estrogen ratios and isoflavone excretion were studied. Urinary isoflavone excretion measurements assessed compliance. RESULTS: Soy isoflavone ingestion induced quantitative differences in urinary excretion of estrogen metabolites and isoflavones but failed to alter 20HE1/16alphaOHE1 ratios. Co-administration of Lactobacillus GG with soy reduced excretion of total and individual isoflavones by 40% (p=0.08), without altering 2OHE1/16alphaOHE1 ratios. CONCLUSION: Isoflavone-rich soy protein administration alone, or with probiotic supplement, did not alter urinary excretion of estrogen metabolites in premenopausal women. However, adding concentrated probiotics may alter isoflavone bioavailability