Dr. Li Zi-Huey
Article Published On
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3 minutes read

If you are wondering whether eating tofu or getting your coffee or tea with soymilk can increase your breast cancer risk, here is what you should know. Knowing the real deal is important, especially now that soy is more common in our diet. Soy is also a popular low-fat source of protein. The relationship between soy food intake and breast cancer has been researched and studied for over 25 years.


Myth   : All soy foods raise your risk for breast cancer.

Fact     : No. Soy products contain isoflavones, which are molecules that are similar to the hormone estrogen. It is this similarity that has led to some theoretical concerns that soy could increase the risk of estrogen-sensitive cancers, including breast cancer. But, studies show that isoflavones are not in fact identical to estrogen. Isoflavones and estrogen do not have the same preference for estrogen receptor binding.  Clinical trials consistently show that the intake of isoflavone does not adversely affect the risk of breast cancer. These studies on humans have not confirmed a link between eating natural soy and developing breast cancer. A 2010 study found no association between phytoestrogen consumption, which includes soy products increased risk for breast cancer. No data is decisive enough to tout soy’s effects on breast cancer risk or any type of cancer.


Myth   : All types of soy have the same effect on the body.

Fact     : Your body may process the natural soy in tofu, miso, and soy milk differently than the kind that’s added to processed foods.

The soy protein isolate found in supplements, protein powders, and meat substitutes are usually stripped of nutrients, such as fiber. According to experts, it’s also a more concentrated form of soy. So you’re much more likely to get a high dose if you’re having protein shakes and soy hot dogs than if you’re eating edamame.

Experts recommend sticking with a moderate amount, or about 1-2 servings, of whole soy a day.

One serving includes:

  • ½ cup tofu
  • ½ cup tempeh
  • ½ cup edamame
  • ½ cup cooked or canned mature soybeans
  • 1 cup soymilk
  • 1 cup soy yogurt
  • ¼ cup soy nuts  
  • 1 Tbsp. miso


Myth   : If you have or had breast cancer, avoid all soy foods.

Fact   Just as eating a moderate amount of whole soy doesn’t make you more likely to get breast cancer, it also doesn’t seem to raise your risk for recurrence. However, experts recommend that breast cancer patients best avoid soy supplements or processed soy foods.  


Myth   : Eat soy to protect against breast cancer.

Fact     : While eating a moderate amount of soy is fine, it’s too soon to suggest eating more to protect your breasts.  In one report, researchers analyzed data from diet surveys completed by more than 9,500 American and Chinese women. Those who said they ate the most soy were 25% less likely to have their cancer return compared to those who had the least.  Some experts worried that soy might interfere with breast cancer drugs that lower estrogen levels, such as tamoxifen. But the same study showed that soy also protected against recurrence in patients who took tamoxifen. The soy foods that the study included were tofu, soy milk, and fresh soybeans. As you might expect, Chinese women ate far more of it than those in the U.S.  “The results are promising, but there’s still not enough information,” says experts. Experts now believe that soy isoflavones may actually block estrogen from attaching to breast cancer cells instead of spurring growth like once thought.  Many of the hallmark studies are done in Asian countries, where people grow up eating soy in its traditional forms. This may influence the way their body processes soy.


Bottom line   : Choose whole soy rather than processed soy foods. Eat them in moderation as suggested (1-2 servings /day)

In the Shanghai Breast Cancer Survival Study, consuming more soy (more than 2 servings per day) wasn’t linked to risk, but it also showed no added health benefits. A range of soy foods is available to make plant-focused eating habits easy, delicious, and nutritious. Try a switch in focus to look at whole soy foods, like tofu, tempeh, and edamame, for what they offer as a way to cut back on meat, red meat, and eat a more plant-focused, for an overall healthy diet.



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