A number of different foods are made from soybeans, including roasted soy nuts, soy milk and boiled whole soybeans. Soybeans are exceptionally rich in two types of isoflavones, genistein and daidzein. Soy isoflavones are phytoestrogens, which are plant-derived, estrogen-like molecules. These isoflavones have been extensively studied for several different health effects, including reducing the symptoms of menopause.
The Mechanism
When a woman goes through menopause, the level of circulating estrogen drops. The isoflavones in soy-based foods are similar in molecular structure to the female hormone estrogen and have been shown to bind the receptor that normally binds estrogen. However, the effect of soy isoflavones is somewhat complex. In some tissues, soy isoflavones can mimic estrogen and cause estrogen-like effects. However, in other tissues, soy isoflavones have anti-estrogen effects. Thus, the effects of the isoflavones in soy are not straight-forward, and its effects on menopausal symptoms may be due to estrogen-like or anti-estrogen effects.
Research Results
Of the many scientific studies investigating the effects of soy on menopause, many of them have shown that soy significantly reduced the symptoms of menopause, such as hot flashes, night sweats and vaginal dryness. According to the University of Maryland Medical Center, women who were going through menopause experienced hot flashes at a reduced intensity and frequency when they supplemented their diet with soy protein. A strong complicating factor of these research studies is that the effect of the placebo was quite high. Once the numbers were corrected, the true effect of soy on menopausal symptoms was significant, although somewhat modest.
Safety
Soy foods are generally considered safe since people all over the world, especially in Asian countries, have been eating a soy-rich diet for their entire lives. However, Oregon State University notes that the long-term safety of high daily doses of soy protein and isoflavones is not known. Doses of up to 100 mg per day over 6 months appeared to be safe in men and women, but longer-term studies are needed to show whether soy is safe when taken over many years.
Amount of Soy Isoflavones by Type of Soy Food
The amount of soy isoflavones varies in different soy food products and supplements. According to Oregon State University, a 3.5 oz serving of soy protein provides 102 mg of isoflavones; 1/2 cup of miso has 50 mg of isoflavones; 1 oz. of dry-roasted soybeans has 37 mg of isoflavones; 3 oz. of tofu has 20 mg of isoflavones; and 1/2 cup of boiled soybeans provides 12 mg of isoflavones.
How Much Soy?
The clinical studies that show an effect of soy on menopausal symptoms involved 20 to 60 g of soy protein per day, notes the University of Maryland Medical Center. Women who took 15 mg of genistein also had reduced symptoms.
