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Breast Cancer Health Center

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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

Women in the group with the highest intake of soy had a 29% lower risk of death during the study and a 32% lower risk of breast cancer recurrence, compared to women in the group with the lowest intake.

At the four-year follow-up,10.3% of the women in the lowest intake group had died, but 7.4% of those in the highest intake group. Although 11.2% of those in the lowest intake groups had recurrences, 8% of those in the highest group did.

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.

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