METABOLITES OF DIETARY (SOYA) ISOFLAVONES IN HUMAN URINE

This study was undertaken to better understand the metabolic fate of d ietary isoflavones iii humans. Twelve volunteers were challenged with soya flour and urinary diphenol levels were then determined by gas chr omatography (GC) and gas chromatography-mass spectrometry (GC-MS). The presence of previously described urinary diphenols was confirmed, i.e . the isoflavones, daidzein and genistein; the isoflavonoid metabolite s, equol dihydrodaidzein (Int-O-D), O-desmethyl-angolensin (O-Dma); th e lignan enterolactone. Diphenols detected for the first time were the isoflavone, glycitein and five novel isoflavonoid metabolites which a re tentatively identified as 6'-hydroxy-O-desmethylangolensin (6'OH-O- Dma), dihydrogenistein (Int-O-G), dehydro-O-desmethylangolensin (dehyd ro-O-Dma) and two isomers of tetrahydrodaidzein. Urinary excretion rat es of the three isoflavones (daidzein, genistein, glycitein) over a 3- day period following soya challenge showed moderate variation (4 X, 6 X and 12 X, respectively) between the 12 individuals suggesting some i ndividual variabilities in ability to deconjugate and to absorb dietar y isoflavones. However, urinary excretion rates of each of three major isoflavonoid metabolites (equol, O-Dma, 6'OH-O-Dma) showed more marke d variation (922 X, 17 X, 15 X, respectively); while some of this vari ability may reflect varying individual ability to ferment dietary isof lavones per se, an inverse relationship was found between urinary leve ls of equol and both O-Dma and 6'OH-O-Dma suggesting individual variab ility in the preferred metabolic pathways of dietary isoflavones.