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How Much Soy is Too Much?

If animal proteins promote cancer because they boost our blood levels of the growth hormone IGF-1, what about the few plant proteins that have amino acid ratios similar to animal proteins such soy foods? One of soy’s selling points is that it has “high quality” protein, but as I explored in my video Higher Quality May Mean Higher Risk, higher quality protein may mean a higher risk of cancer.

In my 2-min. video Animalistic Plant Proteins, I show that animal protein consumption is associated with significantly higher levels of the cancer promoter IGF-1 and non-soy plant protein is associated with significantly lower levels. There was no significant association with soy protein, though. This suggests that if all we do is replace animal protein with soy protein, we may not see as dramatic a drop in IGF-1 as that enjoyed by those replacing meat, eggs, and dairy with a variety of plant proteins. You can see what lower IGF-1 levels can mean for prostate and breast cancer growth in my videos Ex Vivo Cancer Proliferation Bioassay and The Answer to the Pritikin Puzzle.

In my 3-min. video Too Much Soy May Neutralize Benefits I show that vegans consuming the equivalent of 7-18 servings of soy foods per day may end up with circulating IGF-1 levels comparable to those who eat meat. For more on the cancer reversal study mentioned in the video, see Cancer Reversal Through Diet. It’s important to remember in this discussion that soy food consumption is associated with an array of health benefits. See, for example The Effect of Soy On Precocious Puberty and Soy Foods & Menopause. But how much may be too much?

It seems that 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 a lot of soy appear to have a lower risk of getting breast cancer and a better chance of surviving breast cancer than those who don’t (see Breast Cancer Survival and Soy). So is there some magic number of soyfood servings we should shoot for?

In my 2-min. video, How Much Soy Is Too Much, I run through all the studies to date that have measured the effects of varying levels of soy consumption on IGF-1 levels. Five to ten servings per day increased IGF-1 levels, but two to three servings did not. The bottom-line is that legumes are one of the healthiest things we can eat and should be a part of everyone’s daily diet. This means lentils, peas, and/or beans every day—in fact, ideally every meal! Soy is an excellent choice, but we should probably stick to no more than 3-5 servings a day.

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.

Discuss

Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, 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.


55 responses to “How Much Soy is Too Much?

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  1. Timely! I just finished reading ‘Vegan For Life’ at your suggestion and was planning to radically step up my soy consumption, from seldom to ~3 servings per day. This further eases my concerns about the 3 servings per day level.




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  2. There are several things I’d like to mention with regard to vegetable protein that were not included in this article:

    1. Soy is a high allergen food. See http://www.responsibletechnology.org/gmo-dangers/health-risks/articles-about-risks-by-jeffrey-smith/Genetically-Engineered-Foods-May-Cause-Rising-Food-Allergies-Genetically-Engineered-Soybeans-May-2007

    2. Most (85-90%) USA-grown soy is genetically engineered (GE) and the long-term ramifications of eating GE foods have not been studied long enough in either animals or humans. Several animal studies indicate serious health anomalies can arise.

    3. If switching to high vegetable proteins, consider eating non-GE/GMO, i.e., organically grown, for various reasons. See this http://www.globalresearch.ca/potential-health-hazards-of-genetically-engineered-foods/8148




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      1. I have deadly soy, milk,eggs,banana,latex and avacado allergies! I have had them since I was born, there are literally 56 derivatives of soy! I memorized all of them, my diet consists of meat, fruit, veggies, and made from scratch desserts. Life is extremely hard with allergies, most people don’t have to read labels to find an ok Juice to drink! I can’t eat at a restaurant, I can’t drink anything from Starbucks etc. I have a Healy lifestyle, while I may be skinnier and weigh little, I am healthy and living life to the fullest! Thank you for this article!




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    1. Catherine,

      I’m in Toronto, and I buy soy milk made by a company called Natur-a. I buy the unsweetened variety. All their soy milk is made from whole soybeans, and certified organic and non-GMO, so I have no qualms about enjoying it.




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  3. Too much of anything is not a good thing. Too much protein is actually something vegans must watch out for. Cut tofu in small pieces. Soy is pure protein. I seen SOY BREAD made of soy flour – one single slice has a whopping 5 grams of protein the same as a huge hunk of steak! Yet the soy bread tastes just like regular white bread.




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  4. Dear Doctor Greger: Thank you for all you do and I sure wish I had known of your important service throughout my long life experimenting with food-as-medicine. Ironically, I started my professional life out as a Product Developer & Home Economist for an industry-founding soy “health food” company in the late 1960’s. Fast forward to today and after a lifetime of high-protein plant-based eating which included soy and other legumes (and high-phosphorus seeds and vegetables), I am now in mid-stage CKD, along with millions of other older Americans who can no longer consume our beloved high-phosphorus foods such as soy. My contribution to this subject today is this: kidney disease in its many forms, is one of the fastest rising medical issues in the world; the standard medical dietary advice is pathetic and needs help. They are telling us to eat what has essentially been the last foods we would ever eat – processed grains and the least nutritious vegetables! I wish someone like you would take up this subject and help us figure out how to manage deteriorating kidneys without removing legumes and the mostly high-phosphorus vegetables.




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    1. Seven to eight servings is quite easily done; but, seven to eighteen as Dr. Greger stated, would probably be easy for a vegan bodybuilder.

      One pack of 14 oz. tofu contains five servings of soy at lunch and dinner with veggies. Then add the cup of soy milk you use in you morning cereal, the cup you use in your two cups of coffee and voila … you’re at seven servings of soy.




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    2. Seven to eight is quite easily done, but seven to eighteen as Dr. Greger stated, would probably apply to a vegan bodybuilder.

      A 14 oz. box of tofu contains five servings of soy in one’s lunch and dinner. Then add the cup of soy milk used in a morning cereal, a cup used in two cups of daily coffee, and voila … seven servings of soy a day.




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  5. When you say animal protein does this include fish as a protein source? Many people think that fish is in another category and is therefore a healthy protein.




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    1. Yes, @Fran , this includes fish. You can learn more about why fish is not a health food by looking up “fish” or “seafood” on this web-site’s search engine or under the “Heath Topics” section.




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    2. Yes, fish are living beings and are animals. Watch Earthlings and you will see that our waters are so contaminated that fish are no longer the safer meat. Plus, fish go through as much pain when pulled from their home as humans do when drowning.




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  6. How is “serving” defined. I have no way to understand 2-3 “servings” could be 2-3 grams, could be 2-3 kilograms. I am sure it is neither of those, but how do I measure a “serving”?




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    1. Paul, I’m taking a guess, but I would think a single serving would be 6-8 oz. of soy milk, 1/4 of a block of tofu, one soy patty, or one soy hot dog.




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    2. An answer to this question copied verbatim from the how much soy is to much thread:

      “If 3-5 servings a day (http://nutritionfacts.org/vide… then multiply the amount of grams used in this study (http://www.ncbi.nlm.nih.gov/pu… which was 5-22 grams soy per serving, then you end up with 15 to 110 grams per day of soy which is in the safe range.

      Personally I would look at about 50-60 grams per day for a nice middle ground.”




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  7. I realize that consuming soy has many health benefits -especially lowering cancer risk due to its phytoestrogens. But do these benefits hold true for post-menopausal women? Wouldn’t adding ANY estrogen in under those circumstances be a negative? Thanks.




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    1. Except that soy does not have real estrogens. I’m not an expert, but I can’t see why having some soy pre- or post- menopause would be any problem. If you look at populations which consume soy in traditional diets, it is my understanding that the post menopausal women do very well. Just some thoughts for you.




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      1. Soy contain phytoestrogens that behave like estrogens. When I went through menopause, I had one serving (one slice) of Mori Nu Organic silken tofu per day in a fruit –berry–and banana smoothie, which greatly reduced my hot flashes as long as I did not ingest other foods like coffee, or sugar, or animal foods, which increased the the hot flashes. It worked great!




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  8. After watching lots of your videos, six weeks ago I embarked on a Vegan diet to lower my blood pressure. It was starting to climb (138/87) and since I was not thrilled about going on medication I thought I would take your advice and reverse it with a plant-based diet. After the first couple of weeks of eating vegan I found my blood pressure had risen a bit (140/90) but I continued on being careful to not exceed 1200 sodium. The only new food I was eating were soy protein items such as soy cheese, soy milk, soy protein powder and soy burgers. By the 4th week my blood pressure had jumped to 156/97. I had no idea what was happening, but three days later I ended up in the ER in a hypertensive crisis with my blood pressure soaring to 200/115. I was given IV medications to lower it and went home with a couple of high blood pressure drugs which helped to bring it down to 144/96. I began researching hypertensive crisis and discovered a case report that involved soy and hypertensive crisis. It appeared that in some people soy produced a what is commonly referred to as the “cheese effect”. Essentially, a tyramine overdose which acts as a vasoconstrictor and increases blood pressure. When you combine the soy with all the other vegan ‘tyramine’ containing foods over an extended period of time you end up with the ‘cheese effect’. I don’t know what the odds are of people with this type of sensitivity, but it’s important to let your readers know that if they ever get the opposite result (higher blood pressure vs. lower) after following a plant-based diet that they need to ask their doctor what may be the cause or follow an elimination diet to determine the cause. I did both and found that three days following my crisis I ate soy protein and within an hour my blood pressure had jumped considerably. Currently, I am following a low Tyramine Diet and taking Metoprolo 100 mg a day and my blood pressure has returned to 133/83. I hope to be off the medication soon.




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    1. A plant based diet means eating mostly plants, fruits, and whole grains. A bit of soy is fine but most people who quit meat immediately switch to fake meat replacements which can be just as highly processed as the burgers they are leaving behind. And they contain high levels of sodium.




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  9. Is there a list of all animalistic plant proteins? I’m a 24-year vegan
    with high IGF-1 (197). I eat a few slices of tofu most days, no soy
    milk. I have a serving (3T) of hemp seeds in my daily green smoothie. What other proteins might elevate IGF-1?




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  10. What is your opinion regarding fermented vs unfermented soy. There is so much contradicting advice out there. We eat a decent amount of tempeh, which I know is a very healthy soy option. But I’m nervous about my young kids eating edamame, soy milk, yogurt and ice cream, even if they are all organic. Is there any validity in my concerns?




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    1. The only contradicting information comes from the unscientific Weston Price foundation and their lackeys.

      “Some people who write about soy suggest that fermented soy foods are the most healthy, and that isolated soy proteins are the most unhealthy. Fermented soy foods are tempeh, miso, and natto. As will be discussed below, for the most part, the evidence does not suggest that fermented soy foods are healthier than traditional non-fermented soy foods (such as tofu and soymilk). And much of the research on soy showing benefits has been performed on isolated soy protein.”

      http://www.veganhealth.org/articles/soy_wth




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  11. How about soy for men? I’m sure its fine, but I’m also sure you heard these arguments before, that soy spikes your estrogene levels and its bad for men, etc etc.

    obviously, i know its phytoestrogene. but i would love to see the best studies on the subject showing that it isn’t bad for men.

    thanks




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    1. Just read the wikipedia article on phytoestrogens; current consensus is that they have an array of benefits and they have no effect on men.




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  12. Thanks for this informative article. I’m left with one question: What quantity constitutes “a serving”? Thank you.




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  13. So, 3-5 servings is probably good. But how much is 3-5 servings?

    I found a reference:

    “A rough guide is that one serving of soy equals 1 cup of soymilk, or 1/2 cup of tofu, tempeh, soybeans, or soy meats.”

    http://www.veganhealth.org/articles/soy_wth

    I don’t eat a lot of soy, but I eat a lot of lentils and beans, which I assume are similar… If you take a serving = 1/2 cup, then the amounts you mention, 7-15 servings, sound suspiciously like the entire daily solid diet. One wonders whether the problem is the soy or the lack of non-soy that’s really the problem.

    But seriously. Would it be possible to get a recommendation in cups?




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    1. Each type of soy varies. One serving could mean 1 cup of soymilk, 1/2 cup cooked soy bean, 1/3 cup or 1 oz. soy nuts, 1/2 cup of tofu. I wrote a post about soy here.




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  14. Is an elevated IGF-1 risk widely accepted? I noticed that The Mayo Clinic website states, “IGF-1 or IGFBP-3 IGF-1 cannot be reliably used as risk indicators or
    prognostic markers in breast, colon, prostate, or lung cancer.”




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        1. Thanks for sharing. I read the article because I thought IFG-1 could be a good predictor, or at least show trends. For example, those with more IGF-I tend to have greater risk of cancer. I would still argue this to be true, unless others have research to set me straight? I surely do not mind being wrong or changing my stance. From the mayo article it’s hard to see exactly what citation they are basing the claim and at any rate they use the words “may not be reliable”. Sure, it is not 100% reliable that’s fine. We know simply having more IGF-I doesn’t mean we’re due to develop cancer for certain, however it may mean our risk is higher? Plenty of studies like this one show High levels of IFG-I increase cancer risk. My review on applying the precautionary principle to nutrition and cancer shows “Putative mechanisms by which milk contributes to increased prostate cancer risk include the ability of a large oral calcium
          dose to suppress vitamin D activation [7, 10] and the tendency
          of milk to increase serum IGF-I concentrations [11, 12].” Hopefully this sheds some light on the subject. Thanks again!




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  15. Is soy the only protein-dense vegan food for which the IGF-1 consequence was studied? How about the trendy vegan protein powders, such as rice protein, hemp protein, pea protein, etc.? Would one expect the effect here to differ significantly from soy protein isolate or whey protein powders?




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    1. Great questions. Perhaps soy has just been more readily studied? Here are a few studies on pea protein, but nothing on IFG-I I could find. I couldn’t find anything on rice or hemp. Maybe others can jump in? I did conduct some research on whey let me know if that may help?

      Best,
      Joseph




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  16. Does consuming plenty of vegetables with your (soy) protein source moderate IGF-1? This study seems to indicate that may be so:

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2377147/

    “High intakes of vegetables and tomatoes or tomato-containing products
    were associated with lower levels of IGF-I or its molar ratio.” This same study also found that a high intake of polyunsaturated vegetable oils appears to *raise* IGF-1.




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    1. Sure! One serving is equivalent to 1 cup of soy milk, 1/2 cup cooked soy beans, 1/3 cup or 1 oz. soy nuts, and 3-4 oz tofu/tempeh. I write more about this below. Hope that helps.




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  17. Because the amount of soy protein, as measured in grams of protein, varies with each kind of soy food, the question could be framed like this: What is the optimal amount of daily soy protein intake as measured in grams or ounces of protein? (Someone might want to check my figures, below, as well as the framing of the question.)

    1 ounce of tempeh = 5.26 grams of protein

    1 ounce of tofu = 3.16 grams of protein

    3.5 ounces of tempeh = 15.78 grams of protein
    3.5 ounces tofu = 12.1 grams of protein




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  18. Unfortunately I think these studies are showing that we are better off using whey and egg proteins for bodybuilding purposes since the IGF-1 is so much higher on soy.




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  19. What is considered a serving of soy? I’m especially interested in what amount of tofu is a serving and what amount of say, Gardein brand meatless foods would be considered a serving? Sure, one could use so many grams of tofu is a serving of soy … but when it comes to the meat alternatives (such as Gardein), you can’t just weigh it because there’s more than just soy in the product.




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  20. Hello Dave,
    Interesting question. First, I disagree with your statement that weightlifting increases circulating IGF-1 “substantially”. Here is the actual quote from the Results section of the abstract to which you provided a link:

    “During the first 13 wk of resistance training, circulating IGF-I increased by approximately 20% in both the 1-SET and 3-SET groups (P = 0.041). No further increases occurred between 13 and 25 wk. In the 3-SET group, IGFBP-3 decreased 20% between 13 and 25 wk (P = 0.008). Training did not alter IGFBP-1.” So you’re only talking a 20% increase in the first 13 weeks, and in the next 13 weeks, one type of IGF then DECREASED by 20%.

    Second, there are many benefits to weight training: increased muscle mass, decreased risk of cardiovascular disease, increased self-esteem, etc. So even though IGF-1 may increase slightly, that’s not a good reason to stop weight training. Just like someone who runs, and gets benefits of relaxation, better mental health, lower blood pressure, and better cardio-pulmonary health, should think twice about stopping running if (s)he reads (s)he is at increased risk of knee and hip damage. (Of course in that case, they should consider a less high-impact exercise such as swimming).

    I hope this helps. Dr. Jon




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    1. Hi Jon. No, your answer doesn’t really help. Here’s why: You are correct that weightlifting does not increase cancer risk (according to studies), but it does increase IGF-1 significantly. A 20% increase in IGF-1 is not a small increase. Given a 20% increase in circulating IGF-1, why wouldn’t you expect an increase in cancer risk? When you consume too much protein or animal protein and get a 20% increase in IGF-1, you would expect an increase in cancer risk, yes? Also note that *IGF Binding Protein* decreased in that same study. That is certainly *not* IGF-1. The original question stands: WHY doesn’t a 20% increase in IGF-1 due to weightlifting increase cancer risk? Is a higher circulating IGF-1 not actually a big deal after all? DR. GREGER: CAN YOU CHIME IN HERE PLEASE?




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  21. 7 to 18 servings of soy a day??? One would have to be an idiot to consume that much in a day! There was a story that hit the news a while back about a man in Texas that grew breasts because of his over-consumption of soy milk. The link below appeared in the UK media regarding a London man who encountered the same problems from too much soy in his diet:

    http://worldnewsdailyreport.com/england-man-grows-breasts-after-drinking-too-much-soy-milk/




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