Factors affecting phytoestrogen absorption and metabolism

In plants and, consequently, in soy food products, isoflavones occur in three main biologically active forms  

Glycosides are the predominant forms. Although in humans flavonoids have been shown to be absorbed in their naturally occurring glycosidic forms (Hollman and Katan, 1998), isoflavones are not. It is generally accepted that to be adsorbed by enterocytes across the intestinal wall, isoflavone glycosides 

Recently, some of the specific faecal bacteria involved in the metabolism of dietary isoflavonoids were isolated (Hur et al., 2000). They have been shown to selectively convert genistin and daidzin to their respective aglycones. One of the isolated bacteria, under anoxic conditions, was further shown to metabolise genistein and daidzein to their respective dihydroxy-genistein and dihydroxy-daidzein. In the case of lignans, enterodiol and enterolactone were shown to be excreted in vivo only in rats harbouring a gut microflora (Rowland et al, 1999). 

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