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When it comes to breast cancer: is soy safe?

By Brierley Wright, October 6, 2009 - 10:25am

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When it comes to breast cancer: is soy safe?

Last week I blogged about what to eat right now for better breast health. I received a lot of comments—and concerns—from readers, mostly on the topic of soy. A few months ago, I too started wondering about the connection between soy and breast health. Soy is touted as a food that can prevent breast cancer—and also implicated as one that might promote it. In the last year, I’ve increased how much soy I eat each week because I’ve been eating a more vegetarian-based diet. (Get recipes for some of my favorite meatless meals here.) So, I wanted to know what the science said: is soy safe or not?

Here’s what I found. (You can read the full article here, from EatingWell Magazine’s November/December issue.)

• Researchers still don’t know whether isoflavones—the compounds in soy that act as weak estrogens in the body—spur the growth of tumors by acting like estrogen or prevent breast cancer by competing with the breast’s natural estrogen. Scientists who looked at the effect individual isoflavones from soy had on breast-cancer cells in test tubes have found both results.

• Recent studies, however, which looked at dietary habits, are helping scientists to better understand who might reap the greatest protection from soy. One study of nearly 74,000 Chinese women, age 40 to 70, found those who consumed a daily serving or more of soy had a significantly lower risk of developing breast cancer in their premenopausal years than women who ate soy less frequently. Also in this study, the women who started eating soy consistently in adolescence had an even lower risk than those who started later. However, in this study eating soyfoods did not protect women from developing breast cancer after menopause.

• Studies are conflicting about the benefits of soyfood consumption later in life. Researchers hypothesize that in younger women, when the body’s estrogen levels are high, isoflavones in soy may compete with the body’s natural estrogen and reduce risk of breast cancer. After menopause, however, natural estrogen levels are much lower and so it’s thought that the isoflavones act like estrogen. Higher estrogen levels are linked with higher risk for breast cancer. That doesn’t mean that eating soyfoods like tofu and edamame—in moderation—after menopause is unsafe, as there’s no data to show that eating soyfoods increases breast-cancer risk in postmenopausal women. (Find 10 delicious recipes using edamame, tofu and more soy ingredients.)

The Bottom Line: Adding soy to your diet in midlife might not offer much protection against breast cancer. But it probably won’t hurt either: soyfoods are a healthy, protein-rich, low-saturated-fat alternative to foods like red meat. Because theoretically soy isoflavones can act like estrogen, it’s best to eat soyfoods in moderation at any age—up to two servings daily, which is equivalent to 1⁄2 cup tofu or edamame and 1 cup soymilk. Enjoy soy in Tofu Parmigiana and 25 more delicious tofu recipes.

TAGS: Brierley Wright, Health Blog, Food & health news, Nutrition, Wellness

Brierley Wright
Brierley's interest in nutrition and food come together in her position as nutrition editor at EatingWell. Brierley holds a master’s degree in Nutrition Communication from the Friedman School of Nutrition Science and Policy at Tufts University. A Registered Dietitian, she completed her undergraduate degree at the University of Vermont.

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