Soy and breast cancer: an update

Soy and Breast Cancer An Update
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We’ve known that regular soy consumption appears to both prevent breast cancer—the number one cancer killer of young women—and prolong survival in women battling the dreaded disease, but we haven’t understood why.

Soybeans naturally contain weakly estrogenic compounds called phytoestrogens (derived from phyton, the Greek word for “plant”). So the original theory was that the regular presence of the estrogen look-alikes in our bloodstream might trick our body into ramping down actual estrogen production as part of a negative feedback loop, like a thermostat that shuts off the heat when it senses it’s getting too warm.

This theory gained empirical support in 2006 when a group of British researchers showed that indeed the presence of phytoestrogens could effectively down-regulate the enzyme that human cells use to make estrogen (at least in a test tube). The theory fell into disfavor, however, when researchers subsequently failed to show that women who consumed soy ended up with less estrogen circulating in their bloodstream. From a breast cancer standpoint, though, we don’t care how much is in the blood, but how much is in the breast.

A new study just published this month measured estrogen levels inside the breasts themselves of women placed on a high versus low soy diet. This was accomplished by aspirating ductal fluid from the nipple, which is what bathes the very cells most likely to turn cancerous. After 6 months, the researchers found a trend towards lower estrogen levels inside the breasts of women eating two servings of soy foods a day. Not only does this aid our understanding of why soy may shield us from cancer, but can help explain the findings presented in today’s new video-of-the-day, which documents new research suggesting young girls drinking soymilk just twice a week may be protected against premature puberty.

-Michael Greger, M.D.

Image credit: viviandnguyen_ / Flickr

Related videos on premature puberty:
Hormones in Skim vs. Whole Milk
Xenoestrogens & Early Puberty

Related videos on soy:
Soy & Breast Cancer
Soy & Breast Cancer Survival

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  • Michael Greger M.D.
  • http://www.facebook.com/profile.php?id=613285734 Heidi Woodruff

    Why is there so much negative press out there about soy?

  • Mike Quinoa

    Heidi,

    In my opinion, part of it is backlash from the meat and dairy industries who perceive it (rightly) as a threat to their sales. If you quit drinking cow’s milk and start consuming soy milk (the dairy industry doesn’t even want you to use the dreaded term “soy milk”), they’ve just lost a customer. Soy is also widely considered a key, pivotal food (though it doesn’t necessarily have to be) in any vegetarian’s or vegan’s diet. This belief seems to be held by both veg-heads and meat-eaters. If the meat industry can sow the seeds of doubt and fear about soy in the minds of potential vegetarians and thus deter them, they can hold onto a meat-eating customer.

    There is also the issue that some soy foods are in fact probably over-processed, and as famous health icon Jack LaLanne said, “If man made it, don’t eat it.” That’s a good guideline. Anyhow, personally I enjoy my tofu and my unsweetened, organic soy milk without fear.

  • JJ

    I sent this blog post to my step sister who is 42 and just out of surgery, radiation and chemo for breast cancer. Here was her reply:

    “On the article – I generally don’t put much weight on articles about what to eat / not eat as there are so many conflicting views. I’ve seen articles and had nutritionists tell me to avoid soy as ‘studies have found it can cause breast cancer’. So I think it just depends on the person (as in some people may have a different reaction to soy / dairy / etc than others). My personal take on it is there is no prescription for what you should eat (assuming you have a healthy diet to start with, which I think I do) or what you should do other than not internalizing stress. Many of the people I’ve met who’ve had cancer were thin, athletic, vegetarian, etc before they were diagnosed – have yet to meet a fat, alcoholic hamburger guzzling person who smokes 5 packs a day who has cancer, so maybe I should start reconsidering my healthy options ;-)”

    This reply kills me. I really like my step sister. As much as I want to reduce the human population, I’d really like my step sister to make it. How does one reply to something like this? Or maybe there is no reply? She has already made up her mind and facts are not going to change it, because she believes that she has already been given plenty of contradictory facts. What to do???

    As something of an aside question, ARE there really any studies that show that soy *causes* breast cancer?

    Thanks for anyone’s thoughts on this.

  • JJ

    I want to share another response that I got when I tried to tell a co-worker that eating soy was healthy. The response was that too many brands of soy/tofu have hexane in them.

    I did some research on hexane and while some websites seem to imply that hexane is only used in soybean oil production, other websites say that hexane can be found in products like tofu. Do you know how prevailant the problem of hexane is? How bad is hexane? How can it be avoided and still get one’s soy?

    I’d also like to ask about soy and genetically modified food. I get organic soy which I understand to mean that it can’t be a GMO. But my parents are asking about how important it is to avoid GMO food. Cost is an issue for them. I’ve seen websites that say that GMO foods have been shown to cause lots of problems. Are there any studies that link GMO food, especially soy/tofu, to health problems?

    Thanks for any thoughts you may have!

  • JJ

    Two more responses. I sent this blog post to an older cousin who had breast cancer a couple of years ago. She is not a doctor, but she works at a hospital and considers herself well-informed. This was her response:

    “Completely opposite from what I’ve heard but may have to do with the type of breast cancer. I’ll review and let you know what I think.”

    I also sent this blog post to a co-worker who was recently diagnosed with breast cancer. She went through her first chemo treatment recently and it turns out that it completely wiped out her immune system. This is my co-worker’s response:

    “Chemo, unfortunately, does not distinguish between normal fast-growing cells, and cancer cells. White blood cells are among those, and the chemo knocked my white cell count almost to nothing and I got very, very sick. An immune system is a beautiful thing, I have discovered. I ended up in the hospital on Friday, but was well enough to be at home by Sunday, but am under a quarrantine of sorts through Wednesday.
    I have lots of time on my hands here, so appreciate the reading material. Soy is one of those products that absolutely has a lot of medical people divided over its safety and effectiveness related to breast health.”

    Her story puts things in perspective, but it is the last sentence that I want to point out. All of these responses seem to show that spreading the word about healthy eating is a HUGE uphill battle. People are very confused and are getting lots of conflicting information – or are not getting conflicting info and are simply told flat out (as yet another co-worker was told): “Do not eat soy period.”

    What to say to people like this? Nothing? Is it worth spreading this information at all? I’m feeling rather depressed about it after only a few interactions. I can only imagine what you have gone through. What would it take to educate the doctors and nutritionists?

    • Toxins

      JJ, in response to people who have responded to you, I recommend you go through all the other videos Dr. Greger posted about breast cancer and show them the studies. Even I am skeptical when someone shows me an article but a study is more scientific.
      http://nutritionfacts.org/?s=breast+cancer

      • JJ

        Thanks Toxins. I’ve seen them all several times. I’m not the one that needs the education. :-)

        • Toxins

          I posted this not to educate you, but for you to show your friends

    • http://twitter.com/usefulDesign Useful Design

      I think one of the reasons there is so much division amongst healthcare (sickcare) professionals about nutritional issues is that they have no grounding in the concept of holistic thinking on health (nor nutritional education in the first place).

      GPs get told by an industry dairy contains high calcium so to their fragmented way of thinking more dairy = more calcium = stronger bones and less osteo. They don’t consider the other acid forming effects of dairy consumption and what effect that may have on bone health, or health in general.

      Besides MDs are there to treat symptoms and disease not cure it. Hence the rejection of the work on heart disease by Caldwell B. Esselstyn, Jr. M.D, a former heart surgeon who embarked on a quest to cure heart disease which he was became aware surgery was not doing. The very hospital where he was head of surgery for years was the slightest bit interested in a cheaper and more effective control over heart disease which effectively cut out the high-rollers club of heart surgeons.

  • http://www.facebook.com/profile.php?id=765646634 Jana Nielson

    I tweeted today that I really enjoy the taste of my Organic Soy Milk and got several responses. One said that Soy is bad for me. The other told me that only fermented soy should be eaten.

    I am confused.

  • Kelleymac

    I read your info on soy and women with breast cancer. As a women fighting the illness i have to say your not really giving us any real information here. What studies are you referring to so we can research them ourselves? I myself am on estrigen lowering shots once a month. I have already used tamoxifin and femara for 5 years each with positive results. So why would i want to eat any estrogen plant or otherwise? I am interested in what facts you have to share with us. I understand that eating soy before bc is a good thing as the gentler plant estrogen blocks the bodies harshier estrogen and thereby protecing the body from the estrogen. Althogh not all bc’s are estrogen receptive making this issue for some a non issue, but for me my bc is estrogen receptive. So you can understand why i am interested in what you have to say. But am a little flustrated in what little your really telling us in this blog and in your 2 min video. Thanks in advance

    • Toxins

      Kelleymac, I recommend viewing the other videos Dr. Greger posted about breast cancer because they will give you a full profile of soy and other foods to eat.
      http://nutritionfacts.org/?s=breast+cancer

    • JJ

      Kelleymac: Sorry for all the health problems you are dealing with.

      You wrote: “What studies are you referring to so we can research them ourselves?”
      Check out the “Sources Cited” block under each specific video. He usually lists the specific stud(ies) and where possible, even provides links to the study. The trick is, you have to click the “sources cites” text in order to make the sources appear. (It’s true.)

      I’m not sure if you’ve seen the following video, but I think this is the one that talks about soy and tamoxifin (I didn’t re-listen to it). If so, then there are definitely sources cited and you can then look at the original study to see if you think it applies to you or not.
      http://nutritionfacts.org/videos/soy-breast-cancer-survival/

      Hope this helps. Good luck.

  • VIRGINIA

    I AM CONCERNED ABOUT SOY AFTER READING CHAPTER 11 ISOFLAVONES AND HUMAN ESTROGEN RECEPTOR: WHEN PLANTS SYNTHESIZE MAMMALIAN HORMONE MIMETICS. PATRICIA DE CREMOUX AND YVES JACQUOT @ UNIV. PIERRE & MARIE CURIE
    - 2 MOST ACTIVE GENISTEIN METABOLITES ARE EQUOL AND O-DMA AND THAT O-DMA PRODUCED BY 80% OF POPULATION AND EQUOL BY 30-40% OF THE POPULATION SUGGESTING INTER INDIVIDUAL DIFFERENCES. – IT IS GUT BACTERIA DEPENDENT.
    - GLUCURONID > 80% OF ELIMINATED FORM OR SULFATE CONJUGATED AGLYCONES ELIMINATED URINE AND BILE. HOWEVER, BACTERIA CAN CATALYZE DECONJUGATION LEADING TO RE-ABSORPTION THROUGH ENTEROHEPATIC RECYCLING. ACCORDINGLY, A SECOND PLASMA PEAK THAT CORRESPONDS TO RE-ABSORPTION IN BILE IS USUALLY OBSERVED. FINALLY, IT SHOULD BE NOTED THAT ISOFLAVONOID AGLYCONES DISTRIBUTE EASILY IN FAT TISSUE, SUGGESTING THAT RETENTION CAN OCCUR IN WOMAN WITH HIGH BODY MASS INDEX. THIS IS FROM CHAPTER 11. CHAPTER 10 BY AN ITALIAN GROUP STATED OK GENISTEIN PRE-MENOPAUSAL WHEN THERE IS MORE ESTROGEN BINDING TO ER-ALPHA IT PREFERS ER-BETA. POST MENOPAUSAL IT WILL OCCUPY ER-ALPHA.
    I AM POST MENOPAUSAL SO NATURALLY I AM CONCERNED. IT COULD BE THAT JAPANESE ARE PROTECTED FROM OTHER DIETARY HABITS LIKE HIGH OMEGA 3 & LOW OMEGA 6 DIET ALONG WITH GREATER VEGETABLE INTAKE. I AM A RECENT CONVERT OF YOURS TO VEGAN. CAN YOU OR YOUR TEAM GIVE ME FEEDBACK? THE BOOK IS ISOFLAVONES: CHEMISTRY, ANALYSIS, FUNCTION AND EFFECT EDITED BY VICTOR R. PREEDY 2013. YOU CAN READ MOST OF IT ON GOOGLE SCHOLAR.

  • Valerie Heim

    Can lunasin really lower cholesterol and help prevent some cancers? And is it necessary/helpful to take a pure lunasin supplement to get the full benefits?