Genistein

Genistein is a plant-derived isoflavone with the molecular formula C15H10O5, belonging to the wider family of flavonoid polyphenols. It is classified as a phytoestrogen because its ring structure resembles that of the human hormone 17-beta-estradiol, which lets it bind estrogen receptors ^[2]. In plants it commonly occurs joined to a sugar as the glycoside genistin, from which the free, or aglycone, form genistein is released by enzymes during digestion or food processing.

The compound was first isolated in 1899 from dyer's broom (Genista tinctoria), which gave it its name, and its structure was subsequently determined and confirmed by chemical synthesis. In the diet, genistein is most abundant in soybeans and the foods made from them, such as tofu, tempeh, and soy protein, and it is also present in other legumes including lupin, fava beans, kudzu, and red clover ^[2]. Populations that eat soy-rich diets take in considerably more of it than those following a typical Western diet.

Interest in genistein spans several fields ^[1][2][3]. As a phytoestrogen it can act as a weak estrogen or, when the body's own estrogen is plentiful, as an anti-estrogen, behavior that has drawn attention to its possible influence on hormone-sensitive tissues such as the breast, endometrium, and prostate ^[2]. Beyond hormonal signaling, it was identified in the 1980s as a specific inhibitor of tyrosine kinases and has since been studied as a modulator of cell growth and programmed cell death, especially in cancer research ^[1]. Further lines of work examine its effects on bone density, blood lipids, menopausal symptoms such as hot flashes, and glucose metabolism ^[3].

Much of the evidence for genistein comes from laboratory and animal studies, and findings in humans have been more mixed, varying with the dose, the form consumed, and individual differences in metabolism; some people, for instance, convert the related isoflavone daidzein into the more potent metabolite equol, while others cannot ^[2]. Soy foods have a long history of dietary use and are generally recognized as safe, whereas isolated, concentrated genistein is used in research and in some supplements rather than as an approved medicine. Because of its estrogenic activity, its use in hormone-sensitive conditions remains a subject of careful study ^[2].

Dietary soy intake is considered safe for most people, and concentrated genistein is generally well tolerated, but its estrogenic activity warrants caution for people with hormone-sensitive conditions, who should consult a clinician. It can interact with thyroid function and with some medications. High isolated doses are less studied than dietary soy.