Genistein belongs to the isoflavone class of flavonoids. It is also classified as a phytoestrogen. Phytoestrogens are plant-derived nonsteroidal compounds that possess estrogen-like biological activity. Genistein has been found to have both weak estrogenic and weak anti-estrogenic effects.
Genistein is the aglycone (aglucon) of genistin. The isoflavone is found naturally as the glycoside genistin and as the glycosides 6"-O-malonylgenistin and 6"-O-acetylgenistin. Genistein and its glycosides are mainly found in legumes, such as soybeans and chickpeas. Soybeans and soy foods are the major dietary sources of these substances. Nonfermented soy foods, such as tofu, contain higher levels of the genistein glycosides, while fermented soy foods, such as tempeh and miso, contain higher levels of the aglycone.
Genistin is the glycoside form of genistein and the predominant form found in plants. It is generally believed that genistin is metabolized to genistein in the gut.