Phytoestrogens are certain plant constituents that have an estrogenic or estrus producing effect on animal tissues. In layman's terms, they act like hormones upon the system.
More than 300 foods have been shown to contain phytoestrogens. Most food phytoestrogens are from one of three chemical classes, the isoflavonoids, the lignans or the coumestans. Isoflavonoid phytoestrogens are found in beans from the legume family; soybeans and soy products are the major dietary source of this type of phytoestrogens. Lignan phytoestrogens are found in high fiber foods such as cereal brans and beans; flaxseeds contain large amounts of lignans. The coumestan phytoestrogens are found in various beans such as split peas, pinto beans, and lima beans; alfalfa and clover sprouts are the foods with the highest amounts of coumestans. 
Why should I be aware of them?
Phytoestrogens or plant estrogens have been long used in naturopathy and botanical medicine for a wide variety of female complaints including menstrual irregularity, dysmennorrhea, and menopausal symptoms. A few plants contain actual estrone and estradiaol, two estrogens that occur in human beings, but most plants contain related steroidal compounds such as diosgenin and B-sitosterol, or other chemical constituents that have the same effect.
All about plant estrogens
There are many different ways that phytoestrogens may work in the body. The chemical structure of phytoestrogens is similar to estrogen, and they may act as mimics (copies) of estrogen. Working as estrogen mimics, phytoestrogens may either have the same effects as estrogen or block estrogen's effects. Which effect the phytoestrogen produces can depend on the dose of the phytoestrogen. The phytoestrogen can act like estrogen at low doses but block estrogen at high doses. Estrogen activates a family of proteins called estrogen receptors. Recent studies have shown that phytoestrogens interact more with some members of the estrogen receptor family, but more information is needed about how these receptors work, especially in breast cancer. Finally, phytoestrogens acting as estrogen mimics may affect the production and/or the breakdown of estrogen by the body, as well as the levels of estrogen carried in the bloodstream.
Several phytoestrogens have been identified and classified into groups. These groups include flavones, flavanones, flavonols, chalcones, lignans, and isoflavones; the most potent are the isoflavones. Many of these phytoestrogens are found in several fruits, vegetables, and cereal grains, but isoflavones are found only in legumes. A traditional legume-based diet offers 30—60 mg/day of isoflavones, specifically genistein, biochanin, daidzein, and formononetin.
Foods containing plant estrogens
Here are some foods that contain plant estrogens, or phytoestrogens --
Plant estrogens and health
The benefits of adding phytoestrogens to the diet appear very promising. But researchers caution against adding large amounts. Too much of them may cause problems with development and fertility. Plant estrogens should be avoided by people who take certain medications. These include tamoxifen, which is used to treat breast cancer.
- Some studies indicate that phytoestrogens have health benefits including potential reduction in breast cancer, prostate cancer and cardiovascular disease risks, possible protection against osteoporosis (bone loss) and menopausal symptoms. Besides, both flavonoid and lignan phytoestrogens have antioxidant activity.
- During menopause, women have fluctuations in estrogen levels. These hormonal changes may increase the risk of heart disease and osteoporosis. These changes also cause hot flashes, night sweats, insomnia, and headaches. The ability of plant estrogens to reduce these symptoms is now being studied.
- Care should be taken in the use of phytoestrogen supplements that may contain phytoestrogens at levels far higher than in food. Since phytoestrogens can have estrogen-like effects in humans, use of these supplements for a long time could increase breast cancer risk. Moderate consumption of foods high in phytoestrogens is unlikely to have any adverse effects and these foods are generally healthful.
What can I do about them?
Care should be taken in the use of phytoestrogen supplements that may contain phytoestrogens at levels far higher than in food. Since phytoestrogens can have estrogen-like effects in humans, use of these supplements for a long time could increase breast cancer risk. Moderate consumption of foods high in phytoestrogens is unlikely to have any adverse effects and these foods are generally healthful.
It is unclear what role foods containing phytoestrogens play in decreasing breast cancer risk. Women can help themselves stay healthy by eating plenty of fruits, vegetables, whole grains, and beans and by getting plenty of exercise and maintaining a healthy weight.
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