Isoflavone sources and bioavailability

Over the last couple of decades non-nutritional bioactive compounds from plants and their biological effects have received attention. Phytoestrogens, also called “plant estrogens”, with their similar structure to estradiol, act with estrogenic effects when imbibed. The compounds that have received considerable interest are, among others, the Isoflavones, of which significant quantities can be found in most members of the family Leguminosae (Fabaceae). Soy, a member of the leguminosae, is the main nutritional source to these phytoestrogenic isoflavones. Isoflavones are commonly consumed in East Asia but less so in the western world. It is highly suggested that the health effects of isoflavones are dependent on the consumer’s ability to digest the substances. This article reviews these estrogen active, polyphenolic compounds present in soy- and bovine milk for the comparison of isoflavone content, bioavailability, and isoflavone related health effects. The mechanisms are also reviewed. This is done for understanding the eventual importance of these phytoestrogens as a part of the diet, and why variation of sources may be of interest for parts of the population. Preliminary study shows phytoestrogen having a largely positive health effect. But only approximately 30-50% of the population are so called “equol-producers” and for the other half soy may not be an optimal isoflavone source and instead bovine milk may serve as an alternative and/or additional dietary source, as isoflavone metabolites have been traced in cow’s milk.