Does Soy Boost Your Breast Cancer Risk?

Find out what science says

Does Soy Boost Your Breast Cancer Risk?

If you’re at high risk for breast cancer and worry about the implications of eating that plate of tofu stir-fry, don’t put down your chopsticks just yet.

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Soy in its natural form does not rank high on the list of contributing factors for this disease, says oncologist Alberto Montero, MD.

Soy products contain isoflavones, which are molecules that are similar to the hormone estrogen. This similarity has led to some theoretical concerns that soy could increase the risk of estrogen-sensitive cancers, including breast cancer.

But isoflavones are not identical to estrogen. The difference matters.

“When consumed, these compounds break down in your intestinal system into other molecules that are similar in structure to estrogen, but don’t bind as well to the estrogen receptor as regular estrogen,” Dr. Montero says.

Still, when studies suggest a possible correlation between food and cancer, media outlets often overplay them. Consumers may assume these studies show a cause-effect relationship when, in reality, rigorous human studies would be needed to prove a connection.

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“People then worry about something like soy intake, when it may not even be a real risk for breast cancer — and don’t worry as much about other things that are true risk factors,” he says.

Obesity, genetics rank higher than soy

Other possible risk factors for breast cancer — obesity, smoking at an early age, a sedentary lifestyle, or saturated fat intake — are bigger concerns than consuming plant estrogens such as soy, Dr. Montero says. Genetics also play a major role in a person’s risk of developing certain types of breast cancer.

“People worry about something like soy intake, when it may not even be a real risk for breast cancer — and don’t worry as much about other things that are true risk factors,” he says.

On the other hand, studies on humans have not confirmed a link between eating natural soy and developing breast cancer. In fact, some actually dispute it or suggest a protective effect. For example, one 2010 study found no association between phytoestrogen (which includes soy products) consumption and an increased risk for breast cancer. However,  no data is decisive enough to tout soy’s effects on breast cancer risk — or its potential benefits.

Rates of breast cancer are much higher in the United States than in many Asian countries, where soy products are a major diet staple, Dr. Montero says. But those countries also typically feature an overall lower-fat diet and differences in birthrates, both of which affect cancer rates.

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Still, breast cancer has been on the rise lately in these countries as economic changes have led to more westernized habits. One potential culprit: Women there are eating more saturated fat. And saturated fat is a proven risk factor for breast cancer.

Keep it natural

When choosing soy-based products, go for natural options rather than highly processed foods. And eat them in moderation, Dr. Montero advises.

Plant estrogen-based sources such as soy milk, tofu and edamame are all good choices. But make them part of a balanced diet that’s high in fruits and vegetables and low in saturated fats.

Dr. Montero does advise women to avoid soy isoflavone extracts, especially in large doses. As a general rule, you are better off getting your nutrition through food sources than through supplements.

“When you’re taking doses of isoflavones from some vitamin store that are several hundred times higher than what you would ingest from eating tofu or soy milk, that could be a potential problem,” he says.

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