In Brief

A Link Between Soy and Survival

Soybean consumption may be beneficial for some women with breast cancer
June 19, 2017

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It can be confusing to know what to eat to lower your risk of breast cancer. Research is mixed, for example, on whether women should avoid soy foods, such as tofu and soybeans, or try to eat more of them. The question is even trickier for women who already have breast cancer.

Soy foods are high in estrogen-like compounds called isoflavones. In lab studies, isoflavones have been shown to slow the growth of breast cancer cells, and studies of women with breast cancer in Asian countries show a connection between high intakes of isoflavones and increased survival. But other research suggests the estrogen-like effects of isoflavones may make some cancer therapies less effective.

“Soy foods can potentially have an impact, but only as a component of an overall healthy and balanced diet,” Fang Fang Zhang said. Photo: IngimageA recent study by Friedman School researchers provides new evidence that for some women with breast cancer, eating isoflavones may be beneficial.

The study, published in Cancer, followed more than 6,000 North American women with breast cancer and looked at their intake of isoflavones. They compared women who ate the most isoflavones (1.5 milligrams, approximately one serving of soybeans per week) to those who ate the least, and found that for certain groups of women, eating more isoflavones was linked to a 21 percent decrease in death. This decrease was found in women with tumors without hormone receptors—which is about one-third of breast cancer cases—and women who did not receive hormone therapy as a treatment for their breast cancer.

Study lead Fang Fang Zhang, assistant professor and cancer epidemiologist at the Friedman School, said the findings suggest that “especially for women with hormone-receptor-negative breast cancer, soy foods may potentially have a beneficial effect and increase survival.”

Although isoflavones didn’t have the same protective effects in women who received hormone therapy, they were not linked to increased death, implying that soy may not interfere with such drug treatments.

If soy does have benefits for cancer patients, Zhang expects it does not work in isolation. “Soy foods can potentially have an impact, but only as a component of an overall healthy and balanced diet,” she said.