SOYBEAN ISOFLAVONES IMPROVE CARDIOVASCULAR RISK-FACTORS WITHOUT AFFECTING THE REPRODUCTIVE-SYSTEM OF PERIPUBERTAL RHESUS-MONKEYS

Although the beneficial effects of dietary soybean protein compared wi th animal proteins on plasma lipids, lipoproteins and atherosclerosis have been known for about 50 years, it has been uncertain whether thes e effects are due to its amino acid concentrations or other components in soybeans. To assess the effect of soybean protein's alcohol-extrac table components (including the isoflavonic phytoestrogens genistein a nd daidzein) on plasma lipid and lipoprotein concentrations and to est ablish its lack of effect on the reproductive system, we fed 27 peripu bertal male and female rhesus monkeys moderately atherogenic diets in which the source of dietary protein was a soy isolate (20% by weight), either containing phytoestrogens (also termed isoflavones) or with th e phytoestrogens removed by alcohol extraction. The study was a crosso ver design with each period lasting for 6 mo. The phytoestrogen-intact soy protein (compared with the alcohol-extracted soy protein) had fav orable effects on plasma lipid and lipoprotein concentrations, specifi cally by significantly reducing LDL + VLDL cholesterol concentrations in both males and females (similar to 30-40% lower), significantly inc reasing high density lipoprotein cholesterol (HDLC) concentrations for females (similar to 15% higher) and significantly lowering total plas ma cholesterol (TPC):HDLC ratios (similar to 20% lower for males and 5 0% lower for females). The phytoestrogens had no adverse effects on th e reproductive systems of either the males or females, as evaluated by reproductive hormone concentrations and organ weights at necropsy. Th us, the isoflavones in soy protein improve cardiovascular disease risk factors without apparent deleterious effects on the reproductive syst em of peripubertal rhesus monkeys.