Effects of Isoflavones on Bone Metabolism

Abstract

Soy isoflavones are a form of polyphenol contained in soybeans and the kudzu plant. One gram of whole soybeans contains an average of 1.4 mg of soy isoflavones, which include a total of 15 compounds such as the aglycones daidzein, genistein and glycitein, and their conjugated forms with carbohydrates such as glycosyl, acetyl, malonyl and a succinyl form. The daily intake of isoflavones by Japanese is estimated to be 18 mg at the 50th percentile. When ingested by humans, isoflavone glycosides need to be hydrolyzed to aglycone forms in the small intestine prior to absorption. Isoflavones exert biological effects through weak estrogenic activity and/or antioxidant activity. Daidzein is metabolized by intestinal bacteria to equol, which has stronger estrogenic activity. It has been reported that 30‐50％ of ethnic Asians have equol-producing activity. Through their weak estrogenic activity, it has been reported that isoflavones affect bone health, lipid metabolism, hormone-dependent cancers, and menopausal symptoms. This paper summarizes the relationship between soy isoflavone intake and health, especially bone metabolism.