Urinary disposition of the soybean isoflavones daidzein, genistein and glycitein differs among humans with moderate fecal isoflavone degradation activity

Glycitein metabolism was compared with other isoflavones to begin to unders tand the effect of this compound. Total isoflavones of 4.5 mu mol/kg body w eight from soymilk (high in genistein and daidzein) and soygerm (high in da idzein and glycitein) was fed to seven women and seven men. To minimize int erindividual variation, only subjects with moderate fecal isoflavone degrad ation rates (half-lives of daidzein and genistein were 15.7 and 8.9 h, resp ectively) were included. The average 48-h urinary excretion of glycitein, d aidzein and genistein was similar to 55, 46 and 29% of the dose ingested, r espectively, which was significantly different from each other in men and w omen (P < 0.001). Plasma isoflavone concentrations at 6 and 24 h after soym ilk feeding paralleled relative amounts of isoflavones in soymilk (genistei n > daidzein > glycitein) (P < 0.05) in men and women, but plasma isoflavon e concentrations after soygerm feeding did not parallel soygerm isoflavone concentrations in women because genistein and glycitein did not differ from each other at 6 h after feeding. Six hours after soygerm dosing, plasma is oflavone concentrations paralleled soygerm isoflavone levels in men. Based on plasma isoflavone concentrations at 6 h after dosing, the bioavailabilit ies of daidzein and genistein were similar in men and women. At the high gl ycitein dose (soygerm), plasma concentration at 24 h after dosing suggested a modest gender difference in glycitein bioavailability.