Summer 2017

Soy and Survival

Unpacking the science related to diet and breast cancer.

By Erin Lewis

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It can be confusing to know how soy foods, such as tofu and soybeans, affect the risk of developing breast cancer—should women eat more or less of them? The question is even trickier for women who already have breast cancer.

Soy foods are high in compounds called isoflavones, which are shown to slow the growth of breast cancer cells in lab studies. Meanwhile, 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.

A recent study by cancer epidemiologist Fang Fang Zhang and her fellow Friedman School researchers provides new evidence that eating isoflavones may be beneficial for some women with breast cancer. The study, published in Cancer, followed more than 6,000 North American women with breast cancer and looked at their intake of isoflavones. Eating more isoflavones—the equivalent of one serving of soybeans per week—was linked to a 21- percent decrease in death among two groups: women with tumors without hormone receptors (about one-third of breast cancer cases) and women who were not receiving hormone therapy for their cancer.

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

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Soy and Survival

Unpacking the science related to diet and breast cancer.