Isoflavones are candidate selective estrogen receptor modulators (SERMs). Soybean isoflavones being structural analogs of estrogen, therefore, show lower risks than estrogen administered in hormone replacement therapy. SERMs are estrogen receptor (ER) ligands that act as estrogen in bones, while inhibiting the action of estrogen in reproductive organs. The recent clinical efficacy of soy isoflavones in humans may be attributed to their ability to produce equol, a metabolite of daidzein, in the intestinal tract. The effect of equol on ER activation is stronger than that of daidzein. We found that fructooligosaccharides (FOS), types of prebiotics, improved the bioavailability of daidzein, genistein, and equol, thereby, inhibiting bone loss in ovariectomized (OVX) mice. The intake of other prebiotics, such as indigestible sugars and starch, also increased equol production from daidzein and reduced bone loss in osteoporotic rodents. Since daidzein is metabolized by gut microflora in the gastrointestinal tract to form equol or O-desmethylangolensin (O-DMA, another metabolite of daidzein), this metabolism is inhibited by antibiotic treatment. Kanamycin intake inhibited increase in plasma equol and O-DMA concentrations and decreased femoral bone mineral density in the kanamycin-treated OVX subgroups, despite dietary supplementation with daidzein. These results suggest that either equol or O-DMA may be a key factor in the bone-protective effects of daidzein. In this study, the importance of intestinal environment in isoflavone metabolism and bone health will be investigated. In addition, the activities of equol enantiomers in bone will be compared and discussed.

Prebiotics and antibiotics affect isoflavone metabolism and bone loss

256th National Meeting (2018)

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