Isoflavones are flavonoids, but they are also called phytoestrogens because of their oestrogenic activity. Structurally, they exhibit a similarity to mammalian oestrogens and bind to oestrogen receptors a and 3. Apart from basic structural similarities, the key to their estrogenic effect is the presence of the hydroxyl groups on the A and B rings. They are classified as oestrogen agonists but also as oestrogen antagonists since they compete with oestrogen for their receptor. They have also been demonstrated to exert effects that are independent of the oestrogen receptor.
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