Harvard Women's Health Watch

Soy may be okay for breast cancer survivors

Prospective studies show no increased risk of recurrence.

At one time, soy seemed to be just the ticket for women: heart-healthy, good for bones, and helpful for hot flashes. And then there was the low rate of breast cancer in soy-consuming countries. But as so often with "miracle foods," closer study has dampened some of the enthusiasm.

Early research indicated that soy protein could lower LDL (bad) cholesterol, but later studies were so unimpressive that the American Heart Association asked that food companies no longer be allowed to label soy products as helpful in preventing heart disease. It's still unclear whether soy does much for bones or hot flashes. And although some studies suggest that it may protect against breast cancer, other research has found that isoflavones (a component of soy that binds to estrogen receptors) can spur the growth of breast cancer cells in test tubes and animals. There's also some concern that soy's estrogenic activity may interfere with tamoxifen, a drug used to prevent recurrence in women with estrogen-sensitive breast cancer. As a result, some clinicians advise patients with breast cancer to limit their consumption of soy or avoid it altogether.

Now, a large study suggests that breast cancer survivors can safely eat soy foods. The findings, presented in April 2011 at the annual meeting of the American Association for Cancer Research, showed no relationship between soy food consumption and increased risk of recurrence or death among women diagnosed with breast cancer. Headlines trumpeted that soy is "safe" and "risk-free" for breast cancer survivors. But if you are a breast cancer survivor, you're not about to take chances. How good are the data? And how do they fit with other information we have about soy? Let's take a look.

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