Phytoestrogens are a class of chemicals that possess hormonelike properties. Specifically, they can behave like the female hormone estrogen once inside the body. These compounds, which have been studied for their potential to affect breast cancer risk, are found primarily in different types of beans as well as some other high-fiber foods.
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Phytoestrogens can work in various ways inside the body. While they mimic the effect of estrogen at low doses, they can actually block human estrogen at high doses, notes Cornell University. In addition, phytoestrogens can interfere with tumor cell growth, which may help prevent cancer, or they can alter DNA processes, which could have detrimental effects. Because of the different behaviors of phytoestrogens, there is no concrete evidence on whether they can help prevent breast cancer and other hormone-dependent cancers such as ovarian and uterine.
Three Classes of Phytoestrogens
Three different types of phytoestrogens can be found in over 300 foods, according to Cornell University. One class, isoflavones, is found in legumes -- with soybeans being the major source of this form of phytoestrogen. A second class of phytoestrogens, known as lignans, is found in high-fiber foods, including flax, brans, beans and cereal. Finally, coumestans can be found in different kinds of beans, including pinto beans, split peas and lima beans.
The richest sources of phytoestrogens in the human diet include soybeans, red clover, whole grains and flaxseed. Herbs with high concentrations of phytoestrogens include hops, thyme, licorice and verbena, notes NYU Langone Medical Center. Some herbs often thought to have phytoestrogens that in fact do not include saw palmetto, wild yam, chasteberry, ginseng, black cohosh and dong quai. These herbs may, however, mimic the effects of estrogen in certain conditions.
The Linus Pauling Institute notes that the long-term safety of high doses of supplements containing one form of phytoestrogens, soy isoflavones, is still unclear. While diets containing soy and soy products should be considered safe, it may be best to avoid soy supplements, as they can contain higher levels of phytoestrogens. Foods containing phytoestrogens are likely safe and generally considered healthy.