Isoflavone phytoestrogens consumed in soy decrease F-2-isoprostane concentrations and increase resistance of low-density lipoprotein to oxidation in humans

Background: Oxidative damage to lipids may be involved in the etiology of a therosclerosis, cardiovascular disease in general, and cancer. The soy isof lavone phytoestrogens, genistein and daidzein, and equol (a daidzein metabo lite produced by intestinal microflora) are antioxidants in vitro; equol is a particularly good inhibitor of LDL oxidation and membrane lipid peroxida tion. Objective: We sought to investigate the effects of a diet enriched with soy containing isoflavones on in vivo biomarkers of lipid peroxidation and res istance of LDL to oxidation, compared with a diet enriched with soy from wh ich the isoflavones had been extracted. Design: A randomized, crossover design was used to compare diets enriched w ith soy that was low or high in isoflavones in 24 subjects, Plasma concentr ations of an F-2-isoprostane, 8-epi prostaglandin F-2 alpha (8-Epi-PGF(2 al pha)), a biomarker of in vivo lipid peroxidation, and resistance of LDL to copper-ion-induced oxidation were determined, Results: Plasma concentrations of 8-epi-PGF(2 alpha) were significantly low er after the high-isoflavone dietary treatment than after the low-isoflavon e dietary treatment (326 +/- 32 and 405 +/- 50 ng/L, respectively; P = 0.02 8) and the lag time for copper-ion-induced LDL oxidation was longer (48 +/- 2.4 and 44 +/- 1.9 min, respectively; P = 0.017. Lag time for oxidation of unfractionated plasma and plasma concentrations of malondialdehyde, LDL al pha-tocopherol, polyunsaturated fatty acids, and isoflavonoids did not diff er significantly between dietary treatments. Conclusions: Consumption of soy containing naturally occurring amounts of i soflavone phytoestrogens reduced lipid peroxidation in vivo and increased t he resistance of LDL to oxidation, This antioxidant action may be significa nt with regard to risk of atherosclerosis. cardiovascular disease in genera l, and cancer.