Q & A Library
How Safe is Soy?
I keep reading contradictory things about soy and women's health - that it relieves hot flashes, that it doesn't, and that it can cause breast cancer or not. Can you update me on the pros and cons of soy foods for women?
Answer (Published 8/6/2012)
The latest news about soy and women’s health comes from a review of 17 previous studies looking at whether or not soy supplements can help relieve menopausal hot flashes. The researchers from Loma Linda University in California concluded that taking extracts of soy isoflavones, biologically active phytoestrogens (plant estrogens), led to a 21 percent reduction in hot flashes compared to a placebo. While the conclusions of the 17 studies varied, the researchers note that overall they showed a "pattern" of soy isoflavones providing more relief than placebos. (The median amount of soy isoflavones used in the studies was 54 mg taken daily for anywhere from six weeks to 12 months, and researchers reported that supplements providing more than 18.8 mg of the soy isoflavone genistein were more than twice as potent at reducing hot flash frequency than supplements containing less genistein.)
Given the review of this evidence, the researchers suggest that soy isoflavones may be worth a try for some women. However, the study leader advises that women look elsewhere for relief if the soy isoflavones don’t help within four weeks.
Here’s a rundown of the impact of soy products on other aspects of women’s health:
Given the uncertainty of the study results, I continue to advise avoiding concentrated soy supplements entirely. However, I still recommend one to two servings a day of whole soy foods. A serving is a cup of soymilk or one half-cup of tofu, tempeh, edamame or soy nuts. At those amounts you’ll get the benefits of soy without the theoretical risks of taking in too many isoflavones.
Andrew Weil, M.D.
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