Phytoestrogens are plant-derived xenoestrogens functioning as the primary female sex hormone (see estrogen) not generated within the endocrine system but consumed by eating phytoestrogenic plants. Also called "dietary estrogens", they are a diverse group of naturally occurring nonsteroidal plant compounds that, because of their structural similarity with estradiol (17-β-estradiol), have the ability to cause estrogenic or/and antiestrogenic effects.

Their name comes from the Greek phyto = plant and estrogen, the hormone which gives fertility to the female mammals. The word "estrus" -Greek οίστρος- means sexual desire and "gene" -Greek γόνο- is "to generate"). It has been proposed that plants use the phytoestrogens as part of their natural defence against the overpopulation of the herbivore animals by controlling the male fertility.

The similarities, at molecular level, of estrogens and phytoestrogens allow them to mildly mimic and sometimes act as antagonists of estrogen. Phytoestrogens were first observed in 1926, but it was unknown if they could have any effect in human or animal metabolism. In the 1940s it was noticed for the first time that red clover (a phytoestrogens-rich plant) pastures had effects on the fecundity of grazing sheep. Researchers are exploring the nutritional role of these substances in the regulation of cholesterol, and the maintenance of proper bone density post-menopause. Evidence is accruing that phytoestrogens may have protective action against diverse health disorders, such as prostate, breast, bowel, and other cancers, cardiovascular disease, brain function disorders and osteoporosis, though there is no evidence to support their use in alleviating the symptoms of menopause.

Phytoestrogens cannot be considered as nutrients, given that the lack of these in diet does not produce any characteristic deficiency syndrome, nor do they participate in any essential biological function.

Analytical methods are available to determine phytoestrogen content in plants and food.

Read more about PhytoestrogensStructure, Mechanism of Action, Ecology, Avian Studies, Food Sources, Health Risks and Benefits, Ethnopharmacology

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Risk Factors For Breast Cancer - Dietary Factors - Phytoestrogens
... Phytoestrogens have been extensively studied in animal and human in-vitro and epidemiological studies ... Research failed to establish any noticeable benefit and some phytoestrogens may present a breast cancer risk ...
List Of Phytochemicals In Food - Phenolic Compounds
... Petunidin Isoflavones (phytoestrogens) Daidzein (formononetin) – soy, alfalfa sprouts, red clover, chickpeas, peanuts, kudzu, other legumes ... Dihydroflavonols Chalconoids Coumestans (phytoestrogens) Coumestrol – red clover, alfalfa sprouts, soy, peas, brussels sprouts ... Lignans (phytoestrogens) – seeds (flax, sesame, pumpkin, sunflower, poppy), whole grains (rye, oats, barley), bran (wheat, oat, rye), fruits (particularly berries) and vegetables ...
Phytoestrogens - Ethnopharmacology
... Plants used that have been shown to contain phytoestrogens include Pueraria mirifica, and its close relative, kudzu, Angelica, fennel and anise ... In a rigorous study, the use of one such source of phytoestrogen, red clover, has been shown to be safe, but ineffective in relieving menopausal symptoms (black ...
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