Soybeans contain chemicals called isoflavones that are classified as phytoestrogens, chemicals in plants that can mimic estrogen in the body. You might think that estrogen only plays a role in female reproduction; however, estrogen plays a role in regulating gene expression, bone density, blood vessel and skin health as well as metabolic regulation in both men and women. As of 2011, the role of phytoestrogens, such as soy isoflavones, in health is still being actively researched.
Phytoestrogens
Phytoestrogens are chemicals in plants that can, but do not necessarily, mimic estrogen in your body. Phytoestrogens do not reach your body in the same form found in plants: Bacteria in your intestines and your digestive enzymes metabolize them into other chemicals. According to the Linus Pauling Institute, only about one-third of the Western population is capable of metabolizing soy isoflavones into highly-estrogenic forms.
Phytoestrogens and Estrogen
The interactions between phytoestrogens and your natural estrogen can be complex. Phytoestrogens do not bind tightly to the estrogen receptor, a protein in the nucleus of your cells responsible for the effects of estrogen. If your natural estrogen levels are high, phytoestrogens decrease estrogen signaling by competing with estrogen for the estrogen receptor. If low levels of natural estrogen are present, such as in menopause, phytoestrogens increase the effects of estrogen in your body. High levels of phytoestrogens can cause your body to decrease production of estrogen.
Benefits
Soy-rich diets appear to be safe and potentially beneficial. According to Cornell University, studies have found both no effect and a decrease in breast cancer risk with high soy diets; no studies have found an increased risk. Similarly, results have not consistently shown that soy isoflavones normalize hormones during menopause. According to the Linus Pauling Institute, a moderate intake, less than 90 mg per day, of soy isoflavones can stimulate bone formation in women with osteoporosis. Isoflavones from soy have not shown conclusive effects on cholesterol, cardiovascular health or prostate cancer.
Safety
Dietary intake of soy isoflavones from foods is considered safe. Because of the potential to interfere with development, women who are pregnant or breastfeeding should not take high doses of supplemental soy isoflavones, although dietary intake in the mother and soy in infant formula appear safe. The safety of soy isoflavones in those with hormone-sensitive cancers is contested among scientists and doctors; Consult with your healthcare provider about your soy intake if you have a hormone-sensitive cancer.
Phytoestrogens in Soy-Based Foods
Soy isoflavones are more concentrated in mature soybeans than green soybeans, or edamame. Isoflavones are normally found bound to a sugar molecule; Fermentation removes this sugar molecule, increasing the amount ultimately absorbed by your body. The highest food sources of isoflavones are soy protein concentrate, miso and boiled mature soybeans.
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