Is Soy Healthy for Breast Cancer Survivors?

Soyfoods 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So, where did this outdated notion that soy could increase breast cancer risk come from?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?

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

How to Block Breast Cancer’s Estrogen-Producing Enzymes

The vast majority of breast cancers start out “hormone-dependent,” meaning the primary human estrogen, called “estradiol plays a crucial role in [breast cancer] development and progression.” That’s one of the reasons why soy food consumption appears so protective against breast cancer—because soy phytoestrogens, like genistein, act as estrogen-blockers. They block the binding of estrogens, like estradiol, to breast cancer cells.

But, wait a second. “The majority of breast cancers occur [after menopause], when the ovaries have [stopped producing estrogen].” What’s the point of eating estrogen blockers if there’s no estrogen to block? It turns out the breast cancer tumors themselves produce their own estrogen from scratch to fuel their own growth.

Estrogens may be formed in breast tumors by multiple pathways. The breast cancer takes cholesterol, and, using the aromatase enzyme, or two hydroxysteroid dehydrogenase enzymes, produces its own estrogen.

So, there’s two ways to stop breast cancer. One is to use “antiestrogens,” estrogen-blockers, like the soy phytoestrogens, or “the anti-estrogen [drug] tamoxifen…However, another way to block estradiol is by using anti-enzymes” to prevent the breast cancer from making all the estrogen in the first place.

And, indeed, there are a variety of anti-aromatase drugs in current use. In fact, inhibiting the estrogen production has been shown to be “more effective” than just trying to block the effects of the estrogen—”suggesting that the inhibition of estrogen synthesis is clinically very important for the treatment of estrogen-dependent breast cancer.” It turns out soy phytoestrogens can do both.

Using ovary cells taken from women undergoing in vitro fertilization, soy phytoestrogens were found to reduce the expression of the aromatase enzyme. What about in breast cancer cells, though? Breast cancer cells, too—not only suppressing aromatase activity, but the other estrogen-producing enzyme, too.

But, this is in a petri dish. Does soy suppress estrogen production in people too Well, circulating estrogen levels appear significantly lower in Japanese women than American white women. And, Japan does have the highest per capita soy food consumption. But, you don’t know it’s the soy until you put it to the test. Japanese women were randomized to add soymilk to their diet—or not—for a few months. Estrogen levels did seem to drop about a quarter in the soymilk-supplemented group. Interestingly, when they tried the same experiment in men, they got similar results: a significant drop in female hormone levels, with no change in testosterone levels.

These results, though, are in Japanese men and women that were already consuming soy in their baseline diet. So, it’s really just looking at “higher versus lower…soy intake.”

What happens if you give soymilk to women in Texas? Circulating estrogen levels cut in half. Since increased estrogen levels are a “[marker] for high risk for breast cancer,” the effectiveness of soy to reduce estrogen levels may help explain why Chinese and Japanese women have such low rates of breast cancer.

And, what was truly remarkable is that estrogen levels stayed down a month or two, even after they stopped drinking it. This suggests you don’t have to consume soy every day to have the cancer-protective benefit.

Doctor’s Note

Wait, soy protects against breast cancer? Yes, in study after study after study. Even in women at high risk? See BRCA Breast Cancer Genes & Soy.

Even if you already have breast cancer? See Is Soy Healthy for Breast Cancer Survivors?

Even GMO soy? See GMO Soy & Breast Cancer.

Okay, then, Who Shouldn’t Eat Soy? Watch that video too! 🙂

What else can we do to decrease breast cancer risk? See:

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

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

The Most Potent Phytoestrogen (Plant Estrogen) is in Beer

Why do alcoholic men develop man boobs, and other feminine traits? Well, we know estrogens produce feminization, and our liver clears estrogens from the body. And so, the original theory was alcohol-induced liver damage leading to the retention of excess estrogens. The problem was that when they measured estrogen levels, they were not elevated. And even those with cirrhosis of the liver appeared to clear estrogens from the body normally. And also, men’s testicles started shrinking, even before serious liver disease developed.

So, alternative explanations were considered. Well, if it’s not due to estrogens produced endogenously, meaning within the body, maybe alcoholics are being exposed to exogenous estrogenic substances from dietary sources—maybe from phytoestrogens in the plants that alcoholic beverages are made from.

The discovery that plants could contain hormonal compounds was made back in 1951 by two Australian chemists charged with finding out the cause of an epidemic of infertility in sheep, that was ravaging their nation’s wool industry. It took them ten years, but they finally figured out the cause—a compound present in a type of clover called genistein, the same phytoestrogen found in soybeans.

Online, you can read about the dreaded clover disease on scare-mongering websites, but you’ll note they never talk about the difference in dose. To get as much as the sheep were getting from clover, you’d have to drink more than a thousand cartons of soy milk a day, eat 8,000 soy burgers, or about 800 pounds of tofu a day.

This is not to say you can’t overdo it. There are two case reports in the medical literature on feminizing effects associated with eating as few as 14 to 20 servings of soy foods a day. But at reasonable doses, or even considerably higher than the one or two servings a day Asian men eat, soy phytoestrogens do not exert feminizing effects on men.

So, anyways, back in 1951, we realized plant compounds could be estrogenic. Aha, two German researchers realized, maybe that’s why women who handle hops start menstruating. And indeed, they found estrogenic activity in hops, which is the bittering agent used to make beer. They found trace amounts of the soy phytoestrogens, but in such tiny quantities that beer would not be expected to have an estrogenic effect.

But then in 1999, a potent phytoestrogen called 8-prenylnaringenin was discovered in hops—in fact, the most potent phytoestrogen found to date; 50 times more potent than the genistein in soy, an obvious explanation for the menstrual disturbances in female hop workers in the past. Now that we have machines to pick our hops, our only exposure is likely via beer consumption, but the levels in beer were found to be so low, they shouldn’t cause any concern.

But then in 2001, a study on a hops-containing dietary supplement for “breast enhancement” raised the concern that another phytoestrogen in hops, called isoxanthohumol, might be biotransformed by our liver into the more potent 8-PN—which would greatly augment the estrogenic effects of hops. But this was a study done on mice. Thankfully, a study using human estrogen receptors found no such liver transformation.

And so, all seemed fine, until 2005. See, the liver is not the only transformation site inside the human body. The human colon contains trillions of microorganisms with enormous metabolic potential. It’s like a whole separate organ within our body, with a hundred livers’ worth of metabolizing power. So, let’s effectively mix some beer with some poop, and see what happens.

And indeed, up to a 90% conversion was achieved. Up until then, the concentration of 8-PN in beer was considered too low to affect human health. However, these results show that the activity of the intestinal microbial community could more than tenfold increase the exposure concentration. This can explain why you can detect 8-PN in the urine of beer-drinkers for days—because their gut bacteria keep churning it out. Obviously, the amount of straight 8-PN in beer is not the only source of estrogen effects, given this conversion.

So, a decade ago, the question remained, might drinking too much beer cause estrogenic effects and feminize men? I’ll give you the ten-year update in my next video.

Doctor’s Note

Check out the thrilling conclusion in my next video: What are the Effects of the Hops Phytoestrogen in Beer?

Previous phytoestrogen videos include:

What about GMO soy? See GMO Soy and Breast Cancer.

Menstrual health videos include:

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

Phytoestrogens May Offset the Risks of Postmenopausal Breast Cancer

Phytoestrogens May Offset the Risks of Postmenopausal Breast Cancer

Soybeans, sunflower, and pumpkin seeds consumption might decrease postmenopausal breast cancer risk

Phytoestrogens are nonsteroidal chemicals found in plants.

Phytoestrogens structurally resemble the estrogens and may influence the possibility of breast cancer by mimicking estrogenic/antiestrogenic characteristics.

In Western societies, whole grains and maybe soy foods too, contain an abundance of phytoestrogens. A German population of postmenopausal women was used to evaluate the association of phytoestrogen-rich foods and dietary fiber from sunflower and pumpkin seeds with breast cancer risk.

Dietary data were collected using a validated food-frequency questionnaire, which included additional questions phytoestrogen-rich foods. Associations were assessed.

Results indicate towards a proof regarding a decreased postmenopausal breast cancer risk linked to high intake of sunflower and pumpkin seeds and soybeans.

Source: Zaineddin AK, Buck K, Vrieling A, Heinz J, Flesch-Janys D, Linseisen J, Chang-Claude J. Nutr Cancer. 2012;64(5):652-65. doi: 10.1080/01635581.2012.683227. Epub 2012 May 16.

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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