What is genistein?

Isoflavonoids are a group of diphenolic hormone-like compounds of dietary origin that are of great interest particularly because of their anti-carcinogenic potency, but also because of their association with other Western diseases like coronary heart disease.
These isoflavonoids are derived mainly from soy-protein products, while clover seeds and leaves are a rich source of Biochanin A and Formononetin.
Genistein precursors such as Genistin and Biochainin A are converted by the intestinal microflora to Genistein into gut.
Remark Genistein mimics human estrogens:

In research collaborations with scientists in the Department of Medicinal Chemistry here at Ohio State, we are investigating the nature of these potentially conserved signaling and signal transduction pathways. So far evidence suggests possible parallels in apoptotic cell death, estrogen-like and interleukin signaling pathways.
Shown at left is the soybean isoflavone genistein (the small grey structure with red hydroxy groups) binding to the human estrogen receptor ER-Alfa.
Genistein is one of the most potent phytoestrogens. It mimics human estrogens by binding to both ER-Alfa and ER-Beta and has promising anti-breast cancer activity.
Genistein is also a central signal in soybean for the potentiation of defense responses. Interestingly, human estrogens such as estradiol also activate defense potentiation in soybean, possibly by acting as a genistein mimic.