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How Much Soy Is Too Much?

To maintain the low IGF-1 levels associated with a plant-based diet, one should probably eat no more than 3-5 servings of soy foods a day.

October 5, 2012 |
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Supplementary Info

How Much Soy Is Too Much?, 4.8 out of 5 based on 8 ratings

Sources Cited

Shu XO, Zheng Y, Cai H, Gu K, Chen Z, Zheng W, Lu W. Soy food intake and breast cancer survival. JAMA. 2009 Dec 9;302(22):2437-43.

Wu AH, Yu MC, Tseng CC, Pike MC. Epidemiology of soy exposures and breast cancer risk. Br J Cancer. 2008 Jan 15;98(1):9-14.

Nagata C, Shimizu H, Takami R, Hayashi M, Takeda N, Yasuda K. Dietary soy and fats in relation to serum insulin-like growth factor-1 and insulin-like growth factor-binding protein-3 levels in premenopausal Japanese women. Nutr Cancer. 2003;45(2):185-9.

Dewell A, Weidner G, Sumner MD, Barnard RJ, Marlin RO, Daubenmier JJ, Chi C, Carroll PR, Ornish D. Relationship of dietary protein and soy isoflavones to serum IGF-1 and IGF binding proteins in the Prostate Cancer Lifestyle Trial. Nutr Cancer. 2007;58(1):35-42.

Arjmandi BH, Khalil DA, Smith BJ, Lucas EA, Juma S, Payton ME, Wild RA. Soy protein has a greater effect on bone in postmenopausal women not on hormone replacement therapy, as evidenced by reducing bone resorption and urinary calcium excretion. J Clin Endocrinol Metab. 2003 Mar;88(3):1048-54.

Maskarinec G, Takata Y, Murphy SP, Franke AA, Kaaks R. Insulin-like growth factor-1 and binding protein-3 in a 2-year soya intervention among premenopausal women. Br J Nutr. 2005 Sep;94(3):362-7.

Acknowledgements

Images thanks to viviandnguyen_ via Flickr.

Transcript

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. So is there some magic number of soyfood servings we should shoot for?

So far we know that somewhere between 7 and 18 is bad, so more than 18 definitely gets the axe. This two year study found no effect on IGF levels of adding 2 servings of soyfoods day, whether they were tofu, soymilk, soy nuts, or the concentrated soy isolate found plant-based meats, protein bars or protein powder (green with ? region shrinking).

Still got a big range here. This study suggested 5-10 servings a day was bad— increased IGF—so nutritional science has slowly but surely been narrowing it down. Same year in Japan, 3 servings a day cleared the IGF radar… And then… that’s it. That’s all we got so far.

The bottomline is that legumes should be a part of everyone’s daily diet, which means lentils, peas, and/or beans every day, of which soy is an excellent choice, but I recommend that we should probably stick to no more than 3-5 servings a day.

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 Kerry Skinner.

To help out on the site please email volunteer@nutritionfacts.org

Dr. Michael Greger

Doctor's Note

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. See Protein Intake and IGF-1 Production, Higher Quality May Mean Higher Risk, Animalistic Plant Proteins, and Too Much Soy May Neutralize Plant-Based Benefits. For the role soy plays in extending breast cancer survival, see my latest video on the subject Breast Cancer Survival and Soy. I've got two dozen other videos on soy (and hundreds of others on more than a thousand topics).

For some context, please check out my associated blog post: How Much Soy Is Too Much?

If you haven't yet, you can subscribe to my videos for free by clicking here.

  • http://nutritionfacts.org/ Michael Greger M.D.

    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. See Protein Intake and IGF-1 Production, Higher Quality May Mean Higher Risk, Animalistic Plant Proteins, and Too Much Soy May Neutralize Plant-Based Benefits. For the role soy plays in extending breast cancer survival, see my latest video on the subject Breast Cancer Survival and Soy. I’ve got two dozen other videos on soy (and hundreds of others on more than a thousand topics).

    If you haven’t yet, you can subscribe to my videos for free by clicking here.

    • Karen

      I’m having a hell of a time working out how much soya milk, tofu, tempeh, or soya isolate (ie. TVP) is in “a serving” – each site I’ve found on serving sizes has widely varying amounts listed. It’d be really helpful to have pointers to good, solid resources on serving sizes for soya products (in general, I mean; not for each specific product).

      • HemoDynamic, M.D.

        The serving size cited in one of the above studies “Maskarinec” used the Chinese Food Composition Table which counted one serving size as 100 grams.  this is equal to about 3.5 ounces–about the size of a deck of cards.
        Here is a link to the International Food table: http://www.fao.org/docrep/x5557e/x5557e07.htm#pulses, nuts, and seeds.
        If that link doesn’t work then click this one: http://www.fao.org/docrep/x5557e/x5557e00.htm Go down to Table 1 and click on Pulses, Nuts and Seeds.

        I hope this helps.
        ;-}

        • Misterimpatient

          I appreciate the link to the table. With respect, I don’t actually think that table answers the question. 100 grams of what? The protein (and calories) in 100 grams of tofu is substantially different from the protein in, for example, soy flour. 

          I think the answer everyone is looking for is how many grams of soy protein per day is safe?
          In theory, for a male of my size, I need 60 grams of protein per day. Is it okay if 20 grams per day are soy? How about all 60? Could this be losing the forest for the trees?  Perhaps, but this is a science driven site and solid numbers are part of the science. “Servings” is not a number. Look at junk food servings. They’re all over the place. Thanks again.

          • Toxins

            A cup of soybeans and soy milk = 1 serving
            A half cup of tofu= 1 serving.

            there is no dietary need to supplement protein as all whole plant foods contain complete proteins and caloric intake and expenditure is equivalent to protein needs.

            Soy protein powders are different from soy beans, as this is soy protein isolate lacking all original nutrients found in the bean. Soy protein isolate raises IGF-1 levels in humans twice as much as dairy does in 40 protein gram equivalents.

          • beccadoggie10

            Soy Protein Isolate (powdered soy) is generally recombinant DNA which as a whole bean has received vast amounts of Glyphosate (Roundup), Dicamba, or possible 2,4-D, an herbicide contaminated with 2,3,7,8-TCDDioxins.
            Could that have anything to do with the increased risk of cancer from this form of soya, in addition to it being more concentrated?
            I only use Miso and tofu from certified organic soybeans. Eden Organic miso and MoriNu certified organic soy.

          • HemoDynamic, M.D.

            Misterimpatient,
            Take the time to read the sources cited.  I promise you you will find the answer you are looking for.

          • http://www.facebook.com/emilie.gagniermarandola Emilie Gagnier-Marandola

            Hi. I have read the sources cited. The ONLY number that I was able to find was 11g/day of soy protein in the context that consuming more showed no improved protection against breast cancer. That seems rather low since 100g of tofu has more protein than this. I also looked at the chart that you posted above indicating the protein content in various soy products for 100g. Soy protein content varies greatly. I do not know how to interprete these values. I understand that you want us to search and think for ourselves, and I really have done my best to find the number. Can someone please help me and plainly answer the question: How many grams of soy protein a day should be consumed at most total (not per serving)?

          • HemoDynamic, M.D.

            If 3-5 servings a day (http://nutritionfacts.org/video/how-much-soy-is-too-much/) then multiply the amount of grams used in this study (http://www.ncbi.nlm.nih.gov/pubmed/16176606) 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.

            How much soy is too much for Billy Simmonds below?

          • BrianR

            I agree. I’m trying to find out how many grams of soy protein per day is ideal. Maybe it’s somewhere in the articles that HemoDynamic posted but surely someone has read it and can post here so we don’t all have to read it.

            The most complete article I’ve seen on soy is: http://www.johnrobbins.info/blog/what-about-soy/. When I read it before I understood him to say not to go over 20 grams but I can’t find that now so maybe he’s changed it. Elsewhere it is recommended to have at least 25 grams of soy protein so I would stick to that amount just to be sure unless the info above supersedes it.

          • HemoDynamic, M.D.

            Here is a Video that Dr. Greger make on how much soy. http://nutritionfacts.org/video/how-much-soy-is-too-much/

            Do a search for SOY on the front page search engine and you will be given ample info on how much soy.

    • HemoDynamic, M.D.

      The Joy of Soy!
      ;-}

  • Liz

    Would quinoa fall into the same category as soy since it’s also a whole protein?  I’m sure most people don’t eat as much quinoa as soy, but it increasing in popularity.  There are lots of recipes that call for quinoa and tofu.

    • Veganrunner

      No. Quinoa is a seed.

      • Liz

        I realize that it’s a seed, but it’s a complete protein just like soy and animal products. The point of the video is that since  soy is a complete  protein, like meat, out bodies make more IGF-1.  Since quinoa is a complete protein, like meat, will it also cause our bodies to produce more IGF-1.

      • Toxins

        Quinoa is a seed, but nutritionally it is a grain, as peanuts are bean, but nutritionally a nut, as tomatoes are a fruit, but nutritionally a vegetable.

        • Veganrunner

          Toxins, you are so amusing.

          I guess my point was more that the series was on soy not quinoa.

          Today’s video (0october 9th) will upset quite a few. I hope you are armed with the appropriate articles. Someone has to do it!

          • Toxins

            Ah you mean the paleo diet video? I am always ready to debate a radical paleolithic diet advocate. 

          • Veganrunner

            Yes and I think dr. Greger must enjoy it or he wouldn’t use the word Fad in the title.

            Buckle your seat belts!

    • Thea

       Liz: I don’t
      know if quinoa has been studied as extensively as soy or not.  So, how would we know?

      But I did want to point out that the concept of “complete” protein
      doesn’t make sense.   All proteins are complete proteins.  The
      difference is that some proteins have closer chemical make-ups to human flesh
      compared to other proteins.

      I have also heard about quinoa being a “complete” protein.  Even
      though this description is irrelevant, I would guess that people use it to mean
      that quinoa has a closer profile to mammal proteins, just like soy.  So, I
      think it is possible that your idea could be correct.  But I think it
      would depend on the answer to the question: just how close is the quinoa
      protein to animal protein?  Is the difference significant enough to make
      quinoa behave more like other plant proteins or more like soy?

       

      I don’t think we know the answer to this question.  However, I have an idea for you.  if you are interested, you can go to
      the following site and get protein profiles (amount of each type of amino acid)
      in various foods.  You could use this
      site to compare percentages and see how say soy and quinoa differ in amino acid
      percentages from say chicken and beef. 
       It would be interesting even if
      not conclusive to anything.

      http://nutritiondata.self.com/
      To get to the protein profiles: (1) Type a food at top and press search.  (2) click into the food that you are
      interested in.  (3) scroll to the part
      that mentions the protein and click the little down arrow/tab.  When you do that, you will see a list of the
      amino acids and the amounts of each one. 
      (4) copy that data into a spreadsheet to calculate percentages if you want.

      • BPCveg

        Thea:

        I like the way you answer questions and I think you are very smart!

        • Thea

           Wow.  That’s like the best compliment ever. You have made my day!

          And may I also say that I enjoy reading your posts as well.  I think that the comments under the videos are an important part of this site.  Your good quality comments add to the whole.

    • Toxins

      Liz, the concern is with getting too much of the protein, not just the “completeness” of it which only has to do with ratios. A cup of soybeans has 22 grams of protein while a cup of quinoa has only 8. If IGF-1 levels were an issue with quinoa, which i doubt, one would have to eat several cups worth to get to 1 serving of soy.
      http://nutritiondata.self.com/facts/cereal-grains-and-pasta/10352/2
      http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2925/2

  • Johan Abom

    Very interesting. But how much is the amount of 3-5 servings in “grams of protein, derived from soy”?

    • HemoDynamic, M.D.

      Read my reply to Karen above
      ;-}

  • Maria

    What is considered 1 serving?? 

    • HemoDynamic, M.D.

      Read my reply to Karen above.
      :-}

    • beccadoggie10

      1/2 cup cooked for soy, or the size of a deck of cards, if it’s a slice of tofu.

  • Misterimpatient

    I’m with the folks asking “what is a serving”? For me, a serving has been:

    8 ounces of edamame (in the pod0.
    7 ounces of tofu
    11 ounces (by weight) of plain unsweetened soy milk (about 1/3 of a quart container)

    • HemoDynamic, M.D.

      Read my reply to Karen above.
      :-}

  • Coacervate

    A serving is the amount that will fit int he palm of your hand.  Usually about a half cup or 120 ml.

  • Coacervate

    Dear USAmerica,

    We need you to please adopt the metric system of weights and measures (again).

    Yours truly,
    The World

  • Bgrune

    Didn’t yesterday’s video say that IGF-1 binding increased along with  IGF-1 levels in those eating lots of soy which explained why east Asians who consume lots of soy do not get the cancers of those with high IGF-1 levels obtained from animal protein?

  • Rckamen2

    Thanks for offering the science that finally clears up the controversy!

  • stacy

    Now we know how much soy is “safe” to eat to not raise IGF levels…but what about how much soy is safe to consume to not affect the thyroid and hormone balance due to the possible phytoestrogens and goitergens?

    And does the sprouted soy offer the same “protective benefits” as fermented soy?

    • Toxins

      Goitergens are found in relative abundance in the plant world, not just in soy. Cooking deactivates this compound so goitergens are not of a concern. Phytoestrogens do not have a negative impact on hormonal levels.
      http://nutritionfacts.org/video/dairy-sexual-precocity/

  • Kcin

    Has anyone looked into the effects of hemp seed on IGF.

  • Radamscooks

    So how does this impact the dose of soy isoflavones recommended by PCRM this past April for treating hot flashes?

  • http://www.facebook.com/judith.mcconnell.33 Judith McConnell

    Thanks for your talk tonight at Joyce Beers Community Center!

  • Humbullpie

     I eat extra firm tofu everyday but I don’t know what is one serving. Can someone tell me in grams or ounces?

    • Veganrunner

      Maybe it’s just a US thing but it is on the label here.

      • Toxins

        A half cup of tofu constitutes a serving

  • Bill

    What constitutes a “Serving” of Soy?

    • beccadoggie10

      100 grams constitutes a serving of soy.

  • Mel

    Hi Dr Mike,  I emailed you recently and you asked me to publish in the comments.  I cant find an exact topic that suits so Im asking here:

    1.  Can you explain the difference (in chemistry and the way our bodies utilise it) between “estrogen” from animals and “phytoestrogen” in plants which mimics estrogen in humans?

    2. Is there any evidence for the effects on vegan diets for Poly Cystic Ovarian Syndrome (PCOS) ?

    Thanks again and keep up the good work!

    Mel

  • Angela Drury

    I thoroughly enjoy your videos and am so excited to have found your website, Dr Greger. Thank you for providing this great resource!

    I am new to the principle of limiting animal protein intake to prevent cancer. After reading the ‘China Study’ two years ago, I changed my family’s diet. This was the information that I had been searching for, as my oldest son had been subjected to a lot of x-rays when he was a toddler. The realisation that all this radiation could result in problems later in life, made me hunt for a way of reducing any risks to his health. Since then I have also discovered un-denatured whey protein. The clinical studies certainly indicate that whey is useful for preventing and treating cancer. I immediaitely put my family onto whey protein and find that it certainly boosts the immune system as we all have far fewer colds despite having young children who bring home anything that is going around at school.

    I know that this is off the topic, but after watching all these videos reinforcing the role of animal protein in the promotion of cancer, I cannot help but wonder if whey protein is as good as our experience demonstrates it to be. I wonder if anyone can clarify whether the benefits of un-denatured whey protein (increase in glutathione) outweigh the negatives of consuming animal protein.

    Also, any advice on what else to do to prevent the potential negative effects of the radiation would be appreciated. I am slowly ploughing through all the videos but I will be grateful for any shortcuts.

    Thank you!
    Angela

  • Nikoleseverance

    How many ounces of soy is considered a serving?

    • Nikoleseverance

       Sorry, I didn’t read down.  I see this has already been discussed

  • noelene S.

    Has anyone else come across the suggestion (e.g. as from Share-International.org) that it’s fermented soy which is best for us? That means tempeh, miso and tamari soy sauce – the last two high in sodium!! Does the fermentation process alter the sodium for the better??

    • Thea

      noelene: I have heard several people report that fermented soy is best. However, I have also read (now I can’t remember where) that that is a myth. And Dr. Greger’s videos along with other sources seem to indicate that soy does not have to be fermented to be beneficial. Hope that helps.

    • beccadoggie10

      Naturopath physician, Joseph Mercola, NMD, who is not a vegetarian or vegan, has indicated that the only soy one should eat, assuming it is certified organic, is fermented soy because he says fermented soy has vitamin K2, a little known vitamin which is amongst other data, is beneficial in keeping calcium in the bone and not leaching out into the blood stream. He cites fellow naturopath, (and grass fed meat eater) Kate Rheaume-Bleue, a graduate from Toronto’s Canadian College of Naturopathic Medicine in 2002. More about Dr. Kate at
      http://www.amazon.com/Kate-Rheaume-Bleue/e/B005HEPCWK/ref=ntt_athr_dp_pel_pop_1

      She authored the book: “Vitamin K2 and the Calcium Paradox: How a Little-Known Vitamin Could Save Your Life,” available at http://www.amazon.com/Vitamin-K2-Calcium-Paradox-Little-Known/dp/1118065727.

      Dr. Andrew Weil, M.D. also recommends supplementing with vitamin K2 especially if one has been diagnosed with osteoporosis, which I have. But, I would rather get some vitamin k2 from food and flavor my dark leafy greens with Eden Organic Shiro Miso, which is lower in sodium content than most other misos. According to Eden Foods, the Shiro has 330 mg sodium per tablespoon. Additionally Eden (is certified) Organic and non-GMO Project verified. This is one of the few food company’s worthy of trust, in my opinion.

      I would still be interested in reading Dr. Greger’s input on this book as well as scientific studies.

  • debbie

    what should your igf-1 level be? I have seen many of your videos and I dont find what the level should be?

    • Dr Connie Sanchez, N.D.

      A study to determine normal values of serum IGF-1 in adults, ages 21-70 years old, found that there was no difference in the values observed between healthy men and women. However, a progressive reduction in IGF-1 levels was seen in advancing age. Below is what the study found (1).

      Reference values (mean ± 2 SD) Age IGF-1

      21-25 years 115-345 μg/L

      26-30 years 116-324 μg/L

      31-35 years 112-300 μg/L

      36-40 years 105-280 μg/L

      41-45 years 97-263 μg/L

      46-50 years 90-249 μg/L

      51-55 years 84-236 μg/L

      56-60 years 78-222 μg/L

      61-65 years 72-210 μg/L

      66-70 years 66-198 μg/L

      71-75 years 61-186 μg/L

      76-80 years 57-174 μg/L

      81-85 years 52-164 μg/L

      1. Rosaria P W., Normal values of serum IGF-1 in adults: results from a Brazilian Population. Arq Bras Endocrinol Metab 2010;54/6.

  • Patricia

    Hi, I recently read an article suggesting people should avoid foods such as tofu, soymilk and tofurky because they contain soy protein isolate. The article was concerned with the fact that SPI is highly processed. Granted whole foods are better for me, but as a vegan, I eat a lot of tofu. It’s convenient and tasty. Is SPI really something I should avoid?

    • Thea

      Patricia: I’m not an expert, so I can’t comment authoritatively. However, it is my understanding that normal traditional soy foods like tofu, soymilk, and tempeh contain NO soy protein isolate. Yes, they contain soy protein, which as far as we know is very good for you as part of a traditional soy food. However soy protein and soy protein isolate are two different animals. It’s like talking about beets and beet sugar. One is good for you. The other? No so much.

      Now, “processed” foods (non-traditional foods sold in packages like tofurky and snack bars) on the other hand, often DO have soy protein isolate added. THOSE foods are probably not so good for you in large amounts anyway. At least I have read that soy protein isolates can increase ifg-1 levels as much or more than dairy. I don’t know if that is true or not, just repeating what I have heard.

      I have read several essays and chapters on soy and gone to lectures from experts and watched Dr. Greger’s videos. The bottom line is: the science currently tells us that traditional soy products (including tofu) are not only NOT bad for you, but likely have a protective/healthful effect.

      Hope that helps and best of luck.

  • ConcernedCitizen

    Were the participants involved in this study fed organic soy or GMO soy? Also known as Roundup ready soy crops. That bit of information would be helpful in determining how effective this study was.

  • Miriam

    Thank you so much for this video, being a vegan it’s very helpful. My question is, how much is a serving? (in grams).

  • Lisa

    Tofu, soymilk, soy yogurt are an extract from soy beans, with okara being the remaining pulp. Would eating okara with tofu etc have an effect? Thanks

  • Shawn

    Is there any truth to the idea of soy having a feminizing effect on men?

  • beccadoggie10

    Soy is a legume native to East Asia, widely grown for its edible bean. Quinoa is a grain-like crop grown primarily for its edible seeds. Quinoa is closely related to species such as beets or spinach, according to Wikipedia. Quinoa can be substituted for rice and eaten with soy or other beans and lentils..

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