Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: January 15, 2003
Publication Date: March 15, 2003
Citation: BADGER, T.M., RONIS, M., FANG, N. THE HEALTH EFFECTS OF DIETARY ISOFLAVONES. Zempleni and Daniel, editors. CABI Publishing. Molecular Nutrition. Chapter 14. 2003. p. 201-217. Interpretive Summary: This chapter provides an introduction to the field of isoflavones and health. It provides the reader with an understanding level sufficient to critically evaluate the vast and rapidly growing literature on the actions of isoflavones, especially as they relate to nutrition and health status. The molecular structures of isoflavones in plants and in the body, and the methods most widely used to identify and quantitate isoflavones are described. Soy proteins isolate is used as a model soyfood to demonstrate the human urine and plasma pharmacokinetics of the two most abundant isoflavones in soy, and animal models are used to demonstrate that the molecular forms and concentrations at target tissues. Human exposure to isoflavones throughout the lifecycle are discussed and some of the potential beneficial and adverse health effects are explored, as well as the possible molecular mechanisms underlying these effects. In addition, the controversy related to safety of soy infant formulas is addressed.
Technical Abstract: The soybean is an excellent source of high quality dietary protein and it has several constituents used in food processing and cooking. Soy is processed into tofu, miso, flour, oils, textured fibers, protein concentrates and isolates, and extracted for several phytochemicals such as Bowman-Birk inhibitor of trysin/chymotrypsin, saponins and isoflavonoids. The isoflavonoids are a subcategory of flavonoids, which are a large group of naturally occurring plant constituents distinguished by the basic structure of two aromatic rings joined by a three carbon link. Figure 1 illustrates this structure, plus that of the isoflavanones (which have an oxygen bridge to position 9 of the A ring) and their C ring reduction metabolites, the isoflavanols and isoflavans. Isoflavones in soybeans are characterized by the hydroxylation of carbon 7 of the A ring and carbon 4¿ on the B ring. The three most abundant soy isoflavones are represented by the aglycones daidzein, genistein and glycitein, which are present mainly in the glycoside forms, genistin, diadzin and glycitin, as well as several acetylated and malonylated derivatives (Figure 2). It should be noted that there are other well known naturally occurring classes of isoflavonoids, such as the coumestans, rotenoids, pterocarpans, and their are isoflavonoid oligomers. We will focus only on the major soybean isoflavones in this chapter.