A SOY PROTEIN ISOLATE RICH IN GENISTEIN AND DAIDZEIN AND ITS EFFECTS ON PLASMA ISOFLAVONE CONCENTRATIONS, PLATELET-AGGREGATION, BLOOD-LIPIDS AND FATTY-ACID COMPOSITION OF PLASMA PHOSPHOLIPID IN NORMAL MEN

The effects of consuming a soy protein isolate beverage powder (60 g/d for 28 d) vs. a casein supplement was evaluated in 20 male subjects w ho were randomly allocated into the two groups. A dramatic rise in pla sma isoflavone concentrations was observed after supplementation in th e soy protein group, the levels reaching 907 +/- 245 nmol/L for genist ein (a 110-fold increase) and 498 +/- 102 nmol/L for daidzein (a 150-f old increase) as measured by isotope dilution gas chromatography - mas s spectrometry. These concentrations are higher than previously report ed for the plasma of Japanese subjects consuming a traditional diet (2 76 nmol/L and 107 nmol/L, respectively). No significant differences in collagen- or 9,11-dideoxy-11 alpha, 9 alpha-epoxymethanoprostaglandin F-2 alpha (U46619)-induced platelet aggregation were observed in plat elet-rich plasma from the two groups; the increase in plasma isoflavon oids from soy protein supplementation is not sufficient to significant ly inhibit platelet aggregation ex vivo. Similarly, plasma total and H DL-cholesterol were not affected by protein supplementation, possibly because the men were, normocholesterolemic at entry. Analysis of plasm a phospholipid polyunsaturated fatty acid composition showed no differ ences between soy protein and casein supplementation. Previous investi gations reported a significant alteration in fatty acid status in anim als fed soy protein relative to those fed casein. The present studies indicate that although soy protein supplementation to a typical Wester n diet can increase plasma concentrations of isoflavones, this may not necessarily be sufficient to counter heart disease risk factors such as high plasma cholesterol and platelet aggregation.