One reason why soy consumption is associated with improved survival and lower recurrence rates in breast cancer patients may be because soy phytonutrients appear to improve the expression of tumor suppressing BRCA genes.
Why do people who eat legumes—beans, chickpeas, split peas, and lentils live longer? Well, men and women who eat legumes tend to be lighter, have a slimmer waist, lower blood pressure, lower blood sugars, lower cholesterol, lower triglycerides, better kidney function 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 the 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. Soy food intake is associated with longer survival and lower recurrence among breast cancer patients. With an average intake of soy phytonutrients above 17 mg/day, which is about what's found in a cup of soymilk, 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 2 years all of 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 5 years 90% of the tofu lovers were still alive and kicking, where as half of the tofu haters kicked, the bucket. And you see a similar relationship when you look at breast cancer survival and soy protein intake, as opposed to the 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? It does 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 shows 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 2, raging breast cancer. Well if you add soy phytonutrients to the cancer, BRCA gets 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.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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Legumes leading to a longer life? See my last video, Increased Lifespan From Beans.
No matter what genes we inherit, changes in diet can affect DNA expression at a genetic level. For examples see:
I’ve previously covered the available science in Breast Cancer Survival and Soy. Other effects detailed in:
It may be possible to overdo it, though (How Much Soy Is Too Much?).
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