ABSTRACT
The widespread infertility in captive wild animals [1] and grazing livestock [2] led to the discovery of phytoestrogens, chemicals synthesized by vegetables, fruits, and legumes that elicit weak estrogenic effects after dietary consumption [2, 3]. Some phytoestrogens, such as the isoflavones daidzein and genistein (Fig. 1), are considered to possess a structural similarity to the animal estrogen, estradiol [4]. Phytoestrogens have been shown to compete with estradiol for its receptor binding sites (ER) in animal models and are considered antiestrogenic because they cannot elicit a full estrogenic response upon forming a complex with the estrogen receptor in vivo [2, 5, 6]; such understanding led to phytoestrogens being evaluated as preventive or therapeutic agents against hormonedependent diseases, including certain cancers and heart disease [7-9].
