title: Soy consumption alters endogenous estrogen metabolism in postmenopausal women.
abstract: Isoflavones are soy phytoestrogens that have been suggested to be anticarcinogenic. Our previous study in premenopausal women suggested that the mechanisms by which isoflavones exert cancer-preventive effects may involve modulation of estrogen metabolism away from production of potentially carcinogenic metabolites [16alpha-(OH) estrone, 4-(OH) estrone, and 4-(OH) estradiol] (X. Xu et al., Cancer Epidemiol. Biomark. Prev., 7: 1101-1108, 1998). To further evaluate this hypothesis, a randomized, cross-over soy isoflavone feeding study was performed in 18 healthy postmenopausal women. The study consisted of three diet periods, each separated by a washout of approximately 3 weeks. Each diet period lasted for 93 days, during which subjects consumed their habitual diets supplemented with soy protein isolate providing 0.1 (control), 1, or 2 mg isoflavones/kg body weight/day (7.1 +/- 1.1, 65 +/- 11, or 132 +/- 22 mg/day). A 72-h urine sample was collected 3 days before the study (baseline) and days 91-93 of each diet period. Urine samples were analyzed for 10 phytoestrogens and 15 endogenous estrogens and their metabolites by a capillary gas chromatography-mass spectrometry method. Compared with the soy-free baseline and very low isoflavone control diet, consumption of 65 mg isoflavones increased the urinary 2/16alpha-(OH) estrone ratio, and consumption of 65 or 132 mg isoflavones decreased excretion of 4-(OH) estrone. When compared with baseline values, consumption of all three soy diets increased the ratio of 2/4-(OH) estrogens and decreased the ratio of genotoxic: total estrogens. These data suggest that both isoflavones and other soy constituents may exert cancer-preventive effects in postmenopausal women by altering estrogen metabolism away from genotoxic metabolites toward inactive metabolites.
authors.affiliation: Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108, USA.
authors.forename: X
authors.initials: X
authors.lastname: Xu
authors.forename: A M
authors.initials: AM
authors.lastname: Duncan
authors.forename: K E
authors.initials: KE
authors.lastname: Wangen
authors.forename: M S
authors.initials: MS
authors.lastname: Kurzer
mesh_terms: D000704:Analysis of Variance; D016588:Anticarcinogenic Agents / Q000627:therapeutic use* / Q000652:urine; D001943:Breast Neoplasms / Q000517:prevention & control*; D018592:Cross-Over Studies; D004967:Estrogens / Q000378:metabolism* / Q000652:urine; D004968:Estrogens, Non-Steroidal / Q000652:urine; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000627:therapeutic use* / Q000652:urine; D016018:Least-Squares Analysis; D008875:Middle Aged; D048789:Phytoestrogens; D028321:Plant Preparations; D017698:Postmenopause / Q000378:metabolism* / Q000652:urine; D030262:Soybean Proteins / Q000627:therapeutic use* / Q000652:urine
chemical_list: D016588:Anticarcinogenic Agents; D004967:Estrogens; D004968:Estrogens, Non-Steroidal; D007529:Isoflavones; D048789:Phytoestrogens; D028321:Plant Preparations; D030262:Soybean Proteins