Does eating soy increase your breast cancer risk?

This content is sponsored by Regional Cancer Care Associates

Cut to the chase: Soy does not increase your risk of breast cancer, in fact, it may even help fight it.

Several years ago, the connection between soy consumption and breast cancer was a hot button topic, but soy is safe for women with breast cancer, according to the American Institute for Cancer Research. In fact, soy consumption can improve outcomes and reduce mortality rates for breast cancer patients, but there are still lingering doubts about soy’s safety among many breast cancer patients in the United States.

Here’s why: In the early 2000s, there were studies where lab mice implanted with human breast cancer cells were given phytoestrogens, which are plant-based isoflavone estrogens. After seeing cancer tumor growth, scientists suggested that patients with estrogen-dependent breast cancer should avoid eating soy products with a high isoflavone content.

However, further research into soy consumption’s effect on breast cancer patients showed that the results in lab animals did not apply to humans. In fact, research actually connected soy intake with “a small reduction in post-menopausal breast cancer overall survival,” according to a 2018 study.

“There’s still a lot of concern that soy products can promote breast cancer growth,” said Dr. Dongmei Wang, an oncologist at Regional Cancer Care Associates. “However, our patients who have breast cancer and are eating soy products have a lower recurrence rate and a lower mortality rate than those patients not eating soy products. It’s very different than what we thought.”

Meta-analysis studies – those that look at many studies on the same topic – related to breast cancer and soy products in Asian countries show a strong trend in the data: Eating soy helps prevent breast cancer in both pre- and post-menopausal women, Wang said.

“In American and European women, the connection is a little weaker,” Wang said. “But there is definitely a similar result, that soy products can prevent breast cancer in post-menopausal women.”

So why does consuming soy work to lower recurrence of breast cancer? Wang said some researchers think it’s because isoflavones – a weak estrogen product – can compete with a strong estrogen product to bind with the estrogen receptor. This can slow down growth and division of the breast cancer cells.

Wang said soy responds positively with Tamoxifen, a selective estrogen receptor modulator that is one of the drugs she uses to treat breast cancer.

“Soy actually behaves like Tamoxifen,” Wang said. “For patients already on Tamoxifen who eat soy, it has a similar beneficial effect, not a detrimental effect. If you’re data driven, this is very interesting evidence against the misconception of this field.”

Breast cancer patients and survivors who want to add more soy to their diets should eat whole-food soy products, such as edamame and tofu, Wang said.

“You need to eat a traditional soy product, not a fake hamburger made out of soy isolate,” she said. “Based on our current data, there’s no harm in taking soy in its whole form. In China and Japan, they’ve been consuming soy products for more than a thousand years, and in that population, breast cancer is much less than in our population.”

Wang said she still regularly fields questions about soy consumption with her breast cancer patients, and she simply asks if they eat vegetables – because plant estrogens are found in all green vegetables.

“I always tell them it’s not practical to avoid any phytoestrogen in your diet, and based on what we know now, there’s absolutely no data to support that notion that soy is not good for breast cancer patients,” she said.

For more information about breast cancer treatment and prevention, visit Regional Cancer Care Associates for details and to schedule an appointment.

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