How Much Soy Should You Eat To Lower Breast Cancer Risk?

So, we know 7 to 18 servings of soy a day may neutralize some of the beneficial effects of avoiding animal protein. At the same time, studies have repeatedly found that women who eat lots of soy appear to have a lower risk of getting breast cancer, and a better risk of surviving breast cancer than those who don’t eat soy. So is there some magic number of soy food servings we should shoot for?

So far we know that somewhere between 7 and 18 may not be so good, so more than 18 definitely gets the axe. This two year study found no effect on IGF levels of adding two servings of soy foods daily, whether they were tofu, soy milk, soy nuts, or the concentrated soy isolate found in plant-based meats, protein bars, or protein powder; still fine.

Still got a big range here. This study suggested 5 to 10 servings a day was bad— increased IGF—so we’re kind of slowly but surely narrowing down the safety window. Same year in Japan; three servings a day cleared the IGF radar. And then, that’s it. That’s all the science we have so far.

The bottom line is that legumes should be a part of everyone’s daily diet, which means lentils, peas, and/or beans, ideally with each of our meals—of which soy is an excellent choice. But, I recommend that we should probably stick to no more than 3 to 5 servings a day.

Doctor’s Notes

This is the fourth in a string of videos on the role plant and animal proteins play in determining levels of the cancer-promoting growth hormone IGF-1. Also see IGF-1 as One-Stop Cancer ShopProtein Intake and IGF-1 ProductionHigher Quality May Mean Higher RiskAnimalistic Plant Proteins; and Too Much Soy May Neutralize Benefits. For the role soy plays in extending breast cancer survival, see Breast Cancer Survival and Soy. And, I’ve got dozens of other videos on soy.

For further context, be sure to check out my associated blog posts: How Much Soy Is Too Much? and Why Less Breast Cancer in Asia?

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

Should Women at High Risk for Breast Cancer Avoid Soy?

Five studies have been performed on breast cancer survival and soy foods, involving more than 10,000 breast cancer patients. And, those who eat more soy live longer, and have a lower risk of the cancer coming back. But, what about women who carry breast cancer genes? Fewer than 10% of breast cancer cases run in families. But, when they do, it’s most likely mutations to one of the tumor suppressor genes—BRCA1 or BRCA2—that defend the integrity of our genes. They are involved in DNA repair, and so, if either one of them is damaged, or has mutations, chromosomal abnormalities can result, which can set us up for cancer.

This idea that we have tumor suppressor genes goes back to famous research in the 60s that showed that if you fuse together a normal cell with a cancer cell, the cancer cell doesn’t turn the normal cell malignant. Rather, the normal cell suppresses the cancerous one. Tumor suppressor genes are typically split up into two types. There are gatekeeper genes that keep cancer cells in check, and caretaker genes that keep the cell from going cancerous in the first place. And, BRCA genes appear able to do both—that’s why their function is so important.

breast-cancer-and-soy-concernsUntil recently, dietary recommendations for those with mutations focused on reducing DNA damage caused by free radicals, by eating lots of antioxidant-packed fruits and vegetables. If your DNA-repair capacity is low, you want to be extra careful about damaging your DNA in the first place. But, what if we could also boost BRCA function?

In my last video on the topic, I showed how, in vitro, soy phytoestrogens could turn back on BRCA protection suppressed by breast cancer, upregulating BRCA expression as much as 1,000% within 48 hours. But, does that translate out of the petri dish and into the person? Apparently so.

Soy intake was only associated with 27% breast cancer risk reduction in people with normal BRCA genes, but a 73% risk reduction in carriers of BRCA gene mutations. So, a healthy diet may be particularly important in those at high genetic risk. Meat consumption, for example, was linked to twice as much risk in those with BRCA mutations—97% increased risk, instead of just 41% increased risk of breast cancer in those with normal BRCA genes.

Doctor’s Note

What about for women without breast cancer genes, or for women who have already been diagnosed? That was the subject of my last video, Is Soy Healthy for Breast Cancer Survivors?. The older video I referred to is BRCA Breast Cancer Genes & Soy.

What is in meat that may increase risk? See, for example:

Featured Image From Authority Nutrition and Livestrong.

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

Is Soy Healthy for Breast Cancer Survivors?

is-soy-healthy-for-breast-cancer-survivorsSoyfoods have become controversial in recent years,…even among health professionals,…exacerbated by misinformation found on the Internet.” Chief among the misconceptions is that soy foods promote breast cancer, because they contain a class of  phytoestrogen compounds called isoflavones. Since estrogens can promote breast cancer growth, it’s natural to assume phytoestrogens might too.

But, people don’t realize there are two types of estrogen receptors in the body—alpha and beta. And, unlike actual estrogen, soy phytoestrogens “preferentially bind to and activate [estrogen receptor beta]. This distinction is important, because the 2 [types of receptors] have different tissue distributions…and often function differently, and sometimes in opposite ways.” And, this appears to be the case in the breast, where beta activation has an anti-estrogenic effect, inhibiting the growth-promoting effects of actual estrogen—something we’ve known for more than ten years. There’s no excuse anymore.

The effects of estradiol, the primary human estrogen, on breast cells are completely opposite to those of soy phytoestrogens, which have antiproliferative effects on breast cancer cells, even at the low concentrations one gets in one’s bloodstream eating just a few servings of soy—which makes sense, given that after eating a cup of soybeans, the levels in our blood cause significant beta receptor activation.

So, where did this outdated notion that soy could increase breast cancer risk come from? The concern was “based largely on research that showed that [the main soy phytoestrogen] genistein stimulates the growth of mammary tumors in [a type of] mouse.” But, it turns out, we’re not actually mice. We metabolize soy isoflavones very differently from rodents. The same soy leads to 20 to 150 times higher levels in the bloodstream of rodents. The breast cancer mouse in question was 58 times higher. So, if you ate 58 cups of soybeans a day, you could get some significant alpha activation, too. But, thankfully, we’re not hairless athymic ovariectomized mice, and we don’t tend to eat 58 cups of soybeans a day.

At just a few servings of soy a day, with the excess beta activation, we would assume soy would actively help prevent breast cancer. And, indeed, “[s]oy intake during childhood, adolescence, and adult life were each associated with a decreased risk of breast cancer.” Those women who ate the most soy in their youth appear to grow up to have less than half the risk.

This may help explain why breast cancer rates are so much higher here than in Asia—yet, when Asians come over to the U.S. to start eating and living like Americans, their risk shoots right up.  For example, women in Connecticut—way at the top of the breast cancer risk heap—in their fifties have, like, ten times more breast cancer than women in their fifties living in Japan. But, it’s not just genetic, since when they move here, their breast cancer rates go up generation after generation, as they assimilate into our culture.

Are the anti-estrogenic effects of soy foods enough to actually change the course of the disease? We didn’t know, until the first human study on soy food intake and breast cancer survival was published in 2009 in the Journal of the American Medical Association, suggesting that “[a]mong women with breast cancer, soy food consumption was significantly associated with decreased risk of death and [breast cancer] recurrence.” Followed by another study, and then another, all with similar findings.

That was enough for the American Cancer Society, who brought together a wide range of cancer experts to offer nutrition guidelines for cancer survivors, to conclude that, if anything, soy foods should be beneficial. Since then, two additional studies have been published, for a total of five, and they all point in the same direction. Five out of five, tracking more than 10,000 breast cancer patients.

Pooling all the results, soy food intake after breast cancer diagnosis was associated with reduced mortality (meaning a longer lifespan) and reduced recurrence—so, less likely the cancer comes back. Anyone who says otherwise hasn’t cracked a journal open in seven years.

And, this improved survival was for both women with estrogen receptor negative tumors and estrogen receptor positive tumors, and for both younger women, and for older women. Pass the edamame.

Doctor’s Note

This is probably the same reason flax seeds are so protective. See Flax Seeds & Breast Cancer Survival: Epidemiological Evidence and Flax Seeds & Breast Cancer Survival: Clinical Evidence.

What about women who carry breast cancer genes? I touched on that in BRCA Breast Cancer Genes & Soy, and it’s the topic of my next video, Should Women at High Risk for Breast Cancer Avoid Soy?

What about genetically modified soy? I made a video abut that too; see GMO Soy & Breast Cancer.

Who Shouldn’t Eat Soy? Glad you asked. Watch that video too! 🙂

Not all phytoestrogens may be protective, though. See The Most Potent Phytoestrogen is in Beer and What are the Effects of the Hops Phytoestrogen in Beer?

In health,

Michael Greger, M.D.

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

Red Clover & Soy for the Treatment of Menopausal Symptoms During Breast Cancer

red-clover-for-menopausal-women-with-breast-cancerDaidzein is an isoflavone found in red clover and soy.  Because Daidzein has estrogenic properties, researchers want to know if it stimulates the growth of estrogen-sensitive breast cancer.   So far the results have been controversial.

Researchers did a review of all research on the use of Daidzein in red clover and soy in the treatment of menopausal symptoms in women who also had breast cancer (1).  They wanted to know if this isoflavone could prevent menopausal symptoms and whether or not women with breast cancer were at risk in taking the natural substance.

They found 131 articles on the topic.  There seems to be no change in menopausal symptoms as found in the articles when the woman took soy or red clover.  A fortunate thing here is that it doesn’t influence any tissues that are responsive to estrogen so that women who want to consume Daidzein are not likely at risk for worsened breast cancer when drinking it as part of the diet.

CONCLUSION: Soy consumption may be associated with reduced risk of breast cancer incidence, recurrence, and mortality. Soy does not have estrogenic effects in humans. Soy intake consistent with a traditional Japanese diet appears safe for breast cancer survivors. While there is no clear evidence of harm, better evidence confirming safety is required before use of high dose (≥ 100 mg) isoflavones can be recommended for breast cancer patients.

Source:

  1. Fritz H, et al. Soy, Red Clover, and Isoflavones and Breast Cancer: A Systematic Review. PLOS. Published Online: November 28, 2013.

Dr. Adem Gunes

Dr. Adem Gunes Dr. Adem Gunes has built the world’s largest database of scientifically tested natural substances with proven effects in cancer treatments. In 2009, he was appointed as the Chief Physician of ProLife Clinic in Innsbruck, Austria, and played a key role in the establishment of the research laboratory. He is also the co-founder of the first Austrian hyperthermia center. Now, Dr. Adem works closely with cancer patients from around the world (including Germany, Thailand, Dubai) to recommend them a complementary cancer clinic or to create a personalized care plan for patients to follow at home.

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