THE VARIABLE METABOLIC RESPONSE TO DIETARY ISOFLAVONES IN HUMANS

The aim of this study was to better understand the metabolic fate of d ietary estrogenic isoflavones in humans. Twelve volunteers were challe nged with soya flour and urinary levels of the isoflavones daldzein (D a), genistein (Gen), and glycltein (Gly), and the isoflavonoid metabol ites equol (Eq) and O-desmethylangolensin (O-Dma) determined by GC and GC-MS. Prior to challenge, Da, Gen, and Gly were present in the urine of all participants at low levels and Eq and O-Dma were present in 9/ 12 and 10/12 participants, respectively. Urinary levels of all five di phenols were increased in each individual on the day following challen ge, returning to approximately prechallenge levels on the second or th ird day past-challenge. Mean past-challenge peak levels of the five di phenols compared with pre-challenge levels were Da (4x), Gen (8x), Gly (5x), Eq (45x), and O-Dma (66x). However, there was considerable indi vidual variation in this metabolic response with peak levels of Eq sho wing the highest variation (1527x). An inverse relationship between 69 and O-Dma excretion was also found post-challenge suggesting individu al variability in the preferred metabolic pathways of dietary isoflavo nes.