isoflavone

Isoflavones are a class of plant-derived polyphenols within the flavonoid family that act as phytoestrogens in humans. They share an isoflavone core and commonly occur in plants as glycosides, which are hydrolyzed during digestion to aglycones. The principal dietary isoflavones are genistein, daidzein, and glycitein, found mainly in soybeans and soy products.

Dietary sources and biosynthesis: Soybeans and soy-derived foods, such as tofu, tempeh, and soy milk, are the richest sources of isoflavones. They are also present in smaller amounts in other legumes. In plants, isoflavone biosynthesis arises from the phenylpropanoid pathway; isoflavone synthase diverts precursors toward the isoflavone core rather than other flavonoid structures.

Metabolism and mechanism of action: After ingestion, isoflavones are absorbed and typically metabolized to various conjugates in the liver, circulating as glucuronides or sulfates. In the gut, daidzein can be converted by microbiota into equol in some individuals, a metabolite with higher estrogenic activity. Isoflavones bind to estrogen receptors, with a relatively higher affinity for ER beta, acting as selective estrogen receptor modulators whose effects are tissue- and dose-dependent. They also exhibit antioxidant properties and can influence signaling pathways, including tyrosine kinases, contributing to diverse biological effects.

Health effects and safety: Population studies link dietary isoflavone intake to potential benefits for bone health, menopausal symptoms, and cardiovascular risk, though randomized trials yield mixed results. Typical dietary consumption is considered safe for most people; high supplemental doses may affect thyroid function in iodine-deficient individuals and could interact with estrogen-sensitive conditions. Individuals with hormone-sensitive cancers should consult healthcare providers about soy isoflavone consumption.