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Soy and Breast Cancer: What's the Link?

What experts say about whether soy is helpful, harmful, or neutral when it comes to breast cancer.
WebMD Feature
Reviewed by Laura J. Martin, MD

To be safe, Jennifer Mukai all but eliminated soy from her diet after being told she had breast cancer in May 2009.

Being of Japanese descent and also health conscious, the Seattle interior designer says she was eating a lot of soy in various forms before her diagnosis.

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“I drank about three-quarters of a cup of soy milk in my coffee twice a day and ate tofu and edamame [soy beans] pretty regularly,” the 44-year-old tells WebMD. “I was also probably getting quite a bit of soy in the meat-substitute products I was eating.”

When she asked her oncologist about it, he advised her to cut way back on the soy foods, saying the jury was still out on its safety for women with a history of breast cancer.

“His thinking was that a little was probably safe, but he said some other oncologists on the staff told their patients to avoid soy completely,” she says.

Is soy safe or even beneficial for women who have had breast cancer and women who might get it? Or is the jury still out, as Mukai’s doctor told her, on soy's role in breast cancer or other cancers?

Experts who spoke to WebMD agreed on some points and disagreed on others, including whether recent research has cleared the air or muddied the waters with regard to soy and breast cancer.

Soy Foods Probably Safe

Once found only in health food stores and Asian markets, soy is now a fixture in the American diet, even among people who have never tried tofu, tempeh, or miso soup.

A cheap source of protein, soy is used in the manufacture of a wide range of highly processed foods, including breads, cookies, crackers, breakfast cereals, soy ‘milk’, non-dairy creamers, imitation cheeses, and even some yogurts.

The experts and researchers interviewed by WebMD say that breast cancer survivors probably have little to fear from eating soy foods in moderation.

They also said that soy supplements, a widely used alternative to hormone therapy for menopause-related hot flashes, should be avoided.

The studies have not found these compounds to be very helpful in terms of reducing hot flashes,” Dana Farber Cancer Center oncologist Wendy Chen, MD, tells WebMD. “And they have not been studied in women with breast cancer, so the risk is not known.”

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