Phytoestrogen

Phytoestrogens mainly belong to a large group of substituted natural phenolic compounds: the coumestans, prenylflavonoids and isoflavones are three of the most active in estrogenic effects in this class. but also occurring elsewhere, e.g. on various forages. Although mycoestrogens are rarely taken into account in discussions about phytoestrogens, these are the compounds that initially generated the interest on the topic. == Mechanism of action ==

Phytoestrogens exert their effects primarily through binding to estrogen receptors (ER). There are two variants of the estrogen receptor, alpha (ER-α) and beta (ER-β) and many phytoestrogens display somewhat higher affinity for ER-β compared to ER-α. In vitro studies show an activation of PPARs at concentrations above 1 μM, which is higher than the activation level of ERs. At the concentration below 1 μM, activation of ERs may play a dominant role. At higher concentrations (>1 μM), both ERs and PPARs are activated. Studies have shown that both ERs and PPARs influence each other and therefore induce differential effects in a dose-dependent way. The final biological effects of genistein are determined by the balance among these pleiotrophic actions. == Ecology ==

Phytoestrogens are involved in the synthesis of antifungal benzofurans and phytoalexins, such as medicarpin (common in legumes), and sesquiterpenes, such as capsidiol in tobacco. Soybeans naturally produce isoflavones, and are therefore a dietary source for isoflavones. and ingredients, and also in cosmetics, plastics, and insecticides. Environmentally, they have similar effects as phytoestrogens, making it difficult to clearly separate the action of these two kind of agents in studies. ==Avian studies==

The consumption of plants with unusual content of phytoestrogens, under drought conditions, has been shown to decrease fertility in quail. Parrot food as available in nature has shown only weak estrogenic activity. Studies have been conducted on screening methods for environmental estrogens present in manufactured supplementary food, with the purpose of aiding reproduction of endangered species. == Food sources ==

Soy-based food products, such as soybeans, miso, tempeh, tofu, meatless soy burgers, and soy protein infant foods contain the highest amounts of isoflavones. The highest concentrations of isoflavones are found in soybeans and soybean products followed by legumes, whereas lignans are the primary source of phytoestrogens found in nuts and oilseeds (e.g. flax) and also found in cereals, legumes, fruits and vegetables. Data from the European Prospective Investigation into Cancer and Nutrition found intakes between 1 mg/d in Mediterranean Countries and more than 20 mg/d in the United Kingdom. == Effects on humans ==

In humans, phytoestrogens are digested in the small intestine, poorly absorbed into the circulatory system, circulate in plasma, and are excreted in the urine. Metabolic influence is different from that of grazing animals due to the differences between ruminant versus monogastric digestive systems. Females It is unclear if phytoestrogens have any effect on the cause or prevention of cancer in women. Some epidemiological studies have suggested a protective effect against breast cancer. Additionally, other epidemiological studies found that consumption of soy estrogens is safe for patients with breast cancer, and that it may decrease mortality and recurrence rates. It remains unclear if phytoestrogens can minimize some of the deleterious effects of low estrogen levels (hypoestrogenism) resulting from oophorectomy, menopause, or other causes. Males It remains under study whether phytoestrogens have any effect on male reproductive physiology. Dietary intake of isoflavones at levels greater than in typical Asian diets does not affect estrogen, testosterone, sperm or semen amounts. and instead indicate that diets, such as the Mediterranean diet, might have a positive effect on male fertility. Infant formula Infant formulas made with soy protein phytoestrogens are considered safe alternatives to formulas containing dairy ingredients, which may be excluded for infants with galactosemia and hereditary lactose intolerance. but their authors did not find any adverse effects. Studies conclude there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy-based infant formula compared to conventional cow-milk formula. The American Academy of Pediatrics states: "although isolated soy protein-based formulas may be used to provide nutrition for normal growth and development, there are few indications for their use in place of cow milk-based formula. These indications include (a) for infants with galactosemia and hereditary lactase deficiency (rare) and (b) in situations in which a vegetarian diet is preferred." ==Ethnopharmacology==

In some countries, phytoestrogenic plants have been used historically in the belief they can treat menstrual, menopausal, and fertility effects. Plants containing phytoestrogens include Pueraria mirifica and kudzu. == See also ==