BRCA Breast Cancer Genes & Soy Consumption Research Results


Why do people who eat legumes—beans, chickpeas, split peas, and lentils—live longer? Well, men and women who eat legumes tended towards being lighter, having a slimmer waist, lower blood sugars, lower cholesterol, lower triglycerides, better kidney function, lower blood pressure, and so—no surprise—may live longer. But, interestingly, bean intake was “a better protectant against mortality in women than men.” They think this may be because cancer was the leading killer of women in this population—especially breast cancer. And, we know that breast cancer survivors who eat soy foods, for example, have a significantly lower likelihood of the cancer recurrence. Eating soy foods appears to protect against the cancer coming back. This 2012 review looked at three prospective human studies done to date, and found that women who ate the most soy had a 29% lower risk of dying from breast cancer, and a 36% lower risk of cancer recurrence. And, a fourth study was since published, and it showed the same thing. “[S]oy food intake is associated with longer survival and lower recurrence among breast cancer patients. With an average intake of soy phytonutrients above 17 milligrams a day, which is about what’s found in a single cup of soy milk, the mortality of breast cancer may be able to be reduced by as much as 38%.

Here’s the survival curve over five years. The purple line represents the survival of the women with the highest soy consumption. As you can see, after two years, all the breast cancer survivors eating lots of soy were still alive. But, a quarter to a third of the women who ate the least soy were dead. And, after five years, 90% of the tofu-lovers were still alive and kicking, whereas half of the tofu-haters kicked the bucket. And, you can see a similar relationship when you look at breast cancer survival and soy protein intake, as opposed to soy phytonutrient intake.

How does soy so dramatically decrease cancer risk, and improve survival? Soy may actually help turn back on BRCA genes. BRCA is a so-called caretaker gene, an oncosuppressor—meaning a cancer-suppressing gene responsible for DNA repair. Mutations in this gene can cause a rare form of hereditary breast cancer, popularized by Angelina Jolie’s public decision to undergo a preventive double mastectomy.

But, only about 5% of breast cancers run in families. So, 95% of breast cancer victims have fully functional BRCA genes. So, if their DNA-repair mechanisms are intact, how did breast cancer form, grow, and spread? Well, tumors do it by suppressing the expression of the gene, through a process called methylation. The gene’s fine, but cancer found a way to turn it off, or at least turn it down—potentially facilitating the metastatic spread of the tumor.

And, that’s where soy may come in. Maybe the reason soy intake is associated with increased survival and decreased cancer recurrence is because the phytonutrients in soy turn back on your BRCA protection—removing the methyl straightjacket the tumor tried to place on it.

So, researchers put it to the test. These are three different types of human breast cancer, specially stained so that the expression of BRCA genes turns up brown. So, this is what full DNA repair would look like—hopefully, what normal breast cells would look like. Lots of brown, lots of BRCA expression. But, instead, we have column two, raging breast cancer.

Well, if you add soy phytonutrients back to the cancer, BRCA does indeed get turned back on. The DNA repair appears to start ramping back up—though this was at a pretty hefty dose, equivalent to about a cup of soybeans.

Their results suggest that treatment with soy phytonutrients “might reverse DNA hypermethylation, and restore the expression” of the tumor-suppressor genes BRCA1 and BRCA2. May help with other breast cancer genes, as well. “Women at increased [genetic] risk of breast cancer may especially benefit from high [soy] intake.”

Doctor’s Notes

Legumes leading to a longer life? See Increased Lifespan from Beans.

No matter what genes we inherit, changes in diet can affect DNA expression at a genetic level. For example, see:

I’ve previously covered the available science in Breast Cancer Survival & Soy. Other effects are detailed in:

It may be possible to overdo beans, though (see How Much Soy Is Too Much?).

For further context, check out my associated blog posts: Top 10 Most Popular Videos of 2013 and Can Eating Soy Prevent Breast Cancer?

If you haven’t yet, you can subscribe to my videos for free by clicking here.

In health,
Michael Greger, M.D.

Michael Greger, M.D., is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous “meat defamation” trial. Currently Dr. Greger proudly serves as the Director of Public Health and Animal Agriculture at the Humane Society of the United

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