The soybean is a commonly consumed source of vegetable-based protein found in many foods, including tofu, tempeh and many meat-substitutes. Soy also contains chemicals that can provide other health benefits and might have an effect on your body's hormones, but there is not enough evidence to definitively state whether soy affects estrogen levels. Always talk to your doctor before making any changes to your diet.
Soy and Isoflavones
Proponents of soy claim that consuming soy-based foods can have a number of effects on your body, including altering your risk of developing certain kinds of cancer and menopause. This is due to the fact that soy contains compounds known as isoflavones. Isoflavones also are known as phytoestrogens because they have a similar chemical structure to the human hormone estrogen. Because human cells respond to estrogen based on its chemical structure, these "plant estrogens" also could affect human cells.
Soy and Breast Cancer
Breast tissue grows in response to increased estrogen levels and many cases of breast cancer also respond to estrogen levels. This means that the isoflavones in soy could affect breast cancer cells; however, because these isoflavones only resemble estrogen, they actually might block the effects of estrogen on breast cancer cells. Women in Asia, who as a group eat more soy-based foods than Western women, have a lower risk of developing breast cancer, which suggests that soy could help block estrogenic signaling that leads to breast cancer. More research is needed to determine the effects of soy on estrogen-related breast cancer development.
Soy and Menopause
Another area where soy is potentially useful is in the treatment of menopause. Many of the symptoms of menopause, such as hot flashes and osteoporosis, are due to the loss of estrogen from the body. In theory, consuming soy products or supplements with soy isoflavones could help reduce some of these symptoms. A 2005 review article in the "American Journal of Medicine" did not find that there is a consistent benefit for menopausal women who consume soy or soy isoflavones.
Considerations
Although soy products might affect estrogen-responsive cells, it is not clear if the isoflavones produce any clinically relevant effects. Talk to your doctor before adding large amounts of soy to your diet or taking soy isoflavone supplements. In some cases, large amounts of soy can promote gout, an extremely painful form of arthritis. Soy supplements should not be used as a supplement for a doctor's care.
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