A SIMPLIFIED METHOD TO QUANTIFY ISOFLAVONES IN COMMERCIAL SOYBEAN DIETS AND HUMAN URINE AFTER LEGUME CONSUMPTION

Reliable and economical quantification of micronutrients in diets and humans is a critical component of successful epidemiological studies t o establish relationships between dietary constituents and chronic dis ease, Legumes are one of the major dietary components consumed by popu lations worldwide, Consumption of legumes is thought to play a major r ole in lowering breast and prostate cancer risk, In this study, a simp lified method that uses solid-phase extraction and gas chromatography was developed to measure isoflavones at levels down to 10 mu g/5 ml. W ith the use of this method, 12.5 g miso (a soybean paste), 12 ounces I somil, and 12 ounces soymilk had daidzin/daidzein levels of 2, 5, and 12.4 mg, respectively, and genistin/genistein levels of 3, 6.5, and 13 .7 mg, respectively, In these products, most of the isoflavones were p resent as glucosides. With the sane method, urinary levels of isoflavo nes in six 15-17-year-old subjects were determined after soymilk inges tion, Each subject was placed on unrestricted nonsoya diets, and three 12-ounce portions of soymilk were given at 12-h intervals, Males excr eted 15.02 +/- 2.74 (SD) mg of daidzein glucuronides/sulfates [mean re covery, 40.4 +/- 7.4% (SD)] by 24 h after the third soymilk ingestion, whereas females excreted 25.56 +/- 5.10 mg (68.7 +/- 13.7%) of daidze in conjugates, which was more than males (P = 0.02). Males and females excreted 7.73 +/- 1.95 mg and 9.11 +/- 0.84 mg of genistein glucuroni des/sulfates (20% recovery of genistin intake), respectively, in the u rine, Most of the isoflavones were excreted within 24 h after ingestio n, The relative urinary levels of daidzein to genistein excreted were significantly (P < 0.05) higher in females than males after the third ingestion, The observed sex difference requires more study since two o f the females are siblings, Thus, the method described can be used to measure isoflavones in soya products and urinary excretion after soya ingestion.