ABSTRACT
I. DEFINITION OF PHYTOESTROGENS Very broadly, the term phytoestrogens refers to plant-derived compounds that show estrogenlike biological activity. In the last decade, attention has been focused on three classes of phytoestrogen: the isoflavonoids, the coumestans, and the lignan precursors (1-5). The main isoflavones are genistein, daidzein, and glycitein. Coumestrol (the most common coumestan) is not an isoflavone, but shares structural similarity with this compound. Isoflavones and coumestrols are found in relatively few foods. The main dietary sources of isoflavones are soybeans and its food products; staples in the traditional Asian diet (6). Sprouts including mung bean sprouts, soybean sprouts, and alfalfa sprouts are the richest source of coumestrol. These sprouts are not commonly consumed and, generally, in modest quantities, even if consumed (1). On the other hand, the lignan precursors, secoisolariciresinol and matairesinol, are ubiquitous in plant foods. Various food groups (e.g., grains and cereals, oilseeds and nuts, berries, fruits, and vegetables) and beverages (e.g., tea, coffee, and wine) are rich sources of these lignan precursors (7-10). Secoisolariciresinol and matairesinol are converted by bacteria in the intestinal tract to enterolactone and enterodiol, respectively (5).
