SUPPLEMENTATION WITH ISOFLAVONOID PHYTOESTROGENS DOES NOT ALTER SERUM-LIPID CONCENTRATIONS - A RANDOMIZED CONTROLLED TRIAL IN HUMANS

Isoflavonoids are a class of flavonoids that are derived in the human diet mainly from soybean-based foods. The major dietary isoflavonoids, genistein and daidzein, have estrogen-like activity and are classed a s phytoestrogens. Because estrogens can lower serum LDL cholesterol an d raise HDL cholesterol, the objective of this study was to determine if isoflavonoids could improve serum lipids in healthy subjects. Forty -six men and 13 postmenopausal women not receiving hormone replacement therapy completed a randomized, double-blind, placebo-controlled tria l of two-way parallel design and 8 wk duration. One tablet containing 55 mg of isoflavonoids (predominantly in the form of genistein) or one placebo tablet was taken daily with the evening meal. Subjects mainta ined their usual diet and physical activity, which were unchanged thro ughout the intervention. Measurement of isoflavonoids and their metabo lites in 24-h urine samples provided an assessment of compliance and o f isoflavonoid metabolism. Serum total, LDL, HDL and HDL subclass chol esterol, triglycerides and lipoprotein (a) were assessed at baseline a nd during the last week of intervention. After adjustment for baseline values, no significant differences in postintervention serum lipid an d lipoprotein (a) concentrations between groups were identified. Furth er adjustment for age, gender and weight change did not alter the resu lts. In addition, changes in urinary isoflavonoids were not significan tly correlated with changes in serum lipids and lipoprotein (a). There fore, this study does not support the hypothesis that isoflavonoid phy toestrogens can improve the serum lipids, at least in subjects with av erage serum cholesterol concentrations.