New Study Finds Soy Beneficial for Breast Cancer Survivors

For years, women were warned away from soy-laden foods due to their associated risk with interfering with breast cancer drugs like tamoxifen. Simultaneously, however, they’ve also heard that soy is good for you; its estrogen-like compounds called isoflavones have been lauded for their ability to inhibit the development or recurrence of breast cancer.

So which one is it?! A new study by  Fang Fang Zhang, a cancer epidemiologist at Tufts University, may have just solved the riddle. She told NPR, “Our finding would suggest that soy food consumption does not have a harmful effect.”

Asia Has It Right

Research completed in Asia in 2009, showed that soy can indeed protect against breast cancer. This inspired Zhang to try and replicate the result in North America. According to the 2009 Asian study, which included 5,000 Chinese breast cancer survivors, it was found that those who consumed the most soy did better than those with lower intakes four years following a breast cancer diagnosis and treatment.

Zhang explained to NPR that because her soy study had a predecessor showing positive results from consumption of the plant, she wasn’t at all surprised to see women in North America benefitting from consuming it too. She has published her findings in the journal Cancer.

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In Zhang’s study, higher consumption of soy was shown to correlate to a longer life after combatting breast cancer. This was particularly applicable to women with hormone receptor negative breast cancers, which often don’t respond to hormone therapy.

For those who were regularly ingesting this plant-based protein, Zhang told NPR, “We found a 21 percent reduction in all-cause mortality among women with the highest dietary intake [of soy], compared to those with the lowest intake.”

However, this increased chance of survival was limited to participants with hormone receptor-negative cancers. For those who had hormone receptor-positive tumors or respond well to hormone therapy, researchers were unable to establish a clear association between soy and survival.

The findings in Zhang’s study were based upon a sample of 6,235 women with breast cancer in the United States and Canada.

Limitations to the Zhang Study

Furthermore, the amount of soy that is typically consumed by a North American female is less than 2 milligrams a day. According to Marian Neuhouser, a registered dietician and nutritional epidemiologist at Fred Hutchinson Cancer Research Center, “If you compare that to Asian populations that on average consume 40 to 50 milligrams, it’s pretty low.”

This small amount of consumption leaves it unclear if the results would remain the same if U.S. women were to consume significantly larger amounts of soy.

However, it is possible to say that soy seems to be safe for women to consume. Even if women in the U.S. consumed a lot more. Neuhouser even extrapolates on this though telling NPR, “It could be beneficial for some women who have had a diagnosis of breast cancer.”