Transformation of Daidzein to Equol and Its Bioactivity

The structures of soybean isoflavones are similar to that of estrogen and have received attention as alternatives to hormone replacement therapy. Daidzein that is a major isoflavone found in soybean is metabolized to equol by intestinal microflora, and the metabolite exhibits a stronger estrogenic activity than daidzein. Recent studies suggest that the clinical effectiveness of isoflavones might be due to their ability to produce equol in the intestine. Although typical laboratory animal species consistently produce high levels of equol, only 30-50% of the human population can produce equol. Fructooligosaccharides, indigestible sugars, increased the bioavailability of daidzein and enhanced the transformation of daidzein to equol by stimulating intestinal microflora. In particular, equol may have indirect and direct effects on bone loss in rodents, osteoporotic models, and osteopenia. Possible bioactivity of equol based on its estrogenic properties with regard to bone metabolism and taking into consideration the status of intestinal microflora is discussed.