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Soy Appears Safe for Breast Cancer Survivors

Moderate Intake of Soy Reduced Breast Cancer Death Risk, Recurrence in Study

Soy and Breast Cancer: Study Results continued...

Women in the lowest soy protein group ate less than 5.31 grams of soy protein daily and about 20 milligrams of isoflavones, while those in the highest ate more than 15.31 grams of soy protein and more than 62.68 milligrams of isoflavones.

But the benefits of soy leveled off, Shu tells WebMD. "After 11 grams of soy protein a day, ''we don't see additional benefits."

"That is about 1/4 cup of firm tofu or 1.5 cups of soy milk,'' she says. "This is a moderate intake."

Of her findings, "I think it's generalizable to the American population," Shu tells WebMD. She points to a study published in November, in which U.S. researchers found in an analysis of nearly 2,000 U.S. breast cancer survivors that soy isoflavones consumed at levels comparable to those in Asian populations may reduce breast cancer recurrence in women getting tamoxifen therapy.

Shu's study was funded by the U.S. Department of Defense Breast Cancer Research Program and the National Cancer Institute. She reported receiving a research development fund from the United Soybean Board in 2005.

Soy and Breast Cancer: Other Opinions

The new study is strong and scientific, says Rachel Ballard-Barbash, MD, MPH, associate director of the Applied Research Program at the National Cancer Institute in Bethesda, Md., who co-authored the editorial. But "the amount of soy food consumed in China is much higher than in the U.S."

That's a point that Shu also makes, writing that the average isoflavone intake in U.S. women is 1 to 6 mg a day, compared with 47 mg a day in the Chinese women.

''It's not quite clear how this [study] extrapolates to U.S. women," Ballard-Barbash says.

''Other differences in these populations may at least partly explain the results," says Marji McCullough, ScD, an American Cancer Society epidemiologist in an email after reviewing the study. ''For example, it is likely that Chinese women have regularly consumed soy throughout their lifetime, whereas in the U.S. consumption is much less common. We don't know whether starting to eat soy regularly after a cancer diagnosis would have the same effect as having a lifelong diet high in soy foods."

What's a breast cancer survivor to do? Moderation may be best. "We think it's unlikely that occasional consumption of soy-based food in the diet would be detrimental," Ballard-Barbash says.

''The study is consistent with our current guidelines for breast cancer survivors, which state that consumption of up to three servings of soy foods per day as part of a healthy diet is safe," McCullough says.

Avoiding high doses such as those found in soy powders and isoflavone supplements should be avoided, she says, because of their possible estrogen-like effects.

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