Doctor's Note

See Protein Intake & IGF-1 Production and Higher Quality May Mean Higher Risk for some immediate background, and IGF-1 as One-Stop Cancer Shop for why we’d like to see these levels low in adulthood (though not in childhood—see Cancer-Proofing Mutation). Is there a level of soy food consumption at which one might see IGF-1 levels comparable to those induced by animal protein? The title of my next video kind of gives it away: Too Much Soy May Neutralize Plant-Based Benefits.

For further context, be sure to check out my associated blog post: How Much Soy Is Too Much?

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  • See Monday’s video Protein Intake and IGF-1 Production and yesterday’s video-of-the-day Higher Quality May Mean Higher Risk for some immediate background and  <a href="IGF-1 as One-Stop Cancer Shop“>IGF-1 as One-Stop Cancer Shop for the reason we’d like to see these levels low in adulthood (though not in childhood—see Cancer-Proofing Mutation). Is there a level of soy food consumption at which one might see IGF-1 levels comparable to those induced by animal protein? The title of tomorrow’s video-of-the-day kind of gives it away: Too Much Soy May Neutralize Plant-Based Benefits.

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

  • Bbfarm

    But this newly released study,, found a positive correlation of low IGF-1 and Alzheimer’s Disease in men.

    • Thea

       Bbfarm:  Interesting study.

      I would like to point out that there are studies showing “that compared to long-time vegetarians, those eating meat (including poultry and fish) appear to have three times the risk of developing dementia.”
      Check out Dr. Greger’s blog post on Alzheimer’s:

      So, if plant eaters have less IGF-1 (as this current set of videos shows) and have less Alzheimers (as the blog post shows), but low IFG-1 might be associated with Alzheimers in men (as your study seems to think), where does that leave us?  Also of interest it to note that your study actually did include women, but found no connection.  The whole thing seems unclear. 

      It would be my off-the-top-of-my-head *guess*/speculation that the study you found is one of those cases where correlation is not related to cause and effect.  But that’s just a hunch.

    • Mike Quinoa

      What’s confusing here is their conclusion: “We report a significant association between low IGF-I and IGFBP-3 serum levels and AD in men, but not in women.”

      The above statement seems to say that low IGFBP-3 is associated with AD in men. But, if I remember correctly, vegans have high levels of IGFBP-3. Maybe this offsets a lower IGF-1. The other obvious question is the comparitive “lowness” of IGF-1 between vegans and sufferers of AD. Maybe men with AD have extremely low IGF-1(?).

      • Plat

        The lowness is because AD lowers igf-1 because those people with AD aren’t eating. Not eating isn’t the same as eating a wfpb or even Paleo for that matter.

        Glad I can be of service.

  • Robinparker

    Hi Dr G, thank you for this recent thread and for the work you do. I’m eating vegan, but concerned of course about getting enough protein, not just because of the misinformed hype about it, but also because after 3 months of vegan eating I feel kind of tired. I am taking b 12. So I’m eagerly following this series of videos and hoping for some practical tips. Best regards from Toronto, Robin Parker

    • Hey Robin,

      I don’t know exactly what your diet is like, but if you consume mostly whole foods, avoiding processed foods (even vegan processed food), you should be fine. 

      As for protein, the Recommended Dietary Allowance (RDA) for yourself would be a calculation:

      1) Divide your weight in pounds by 2.2 to get kilograms.
      2) Multiply your weight in kilograms by 0.8.

      You’ll probably be surprised at how little protein one needs. If you’re an athlete, then you may want to consider the following:

      “Protein recommendations for endurance and strengthtrained athletes range from 1.2-1.7 g/kg (0.5-0.8 g/lb) body weight per day. These recommended protein intakes can generally be met through diet alone, without the use
      of protein or amino acid supplements. Energy intake sufficient to maintain body weight is necessary for optimal protein use and performance.” (p.2)

      However, I assume you’re guessing your low energy level is due to your apparent lack of protein. However, it could be something else. I have heard people say that it could be the withdrawal of steroids from animal products, but I don’t know about that. I’d lean on finding out exactly what you may be lacking.

      At the beginning of the summer, I had lack of energy in my legs and I suspected I was vitamin D deficient from lack of sunshine. I did the blood work and I was correct. So I supplemented D2 (vegan) and got plenty of sunshine. My energy slowly came back, and now it’s much easier for me to do my high intensity workouts; I now run long distances, and easily blast up hills (that includes Riverdale, hehe).

      As a side note: my B12 levels were fine for some reason, but I supplement it anyway.

      What I’m saying is that you may want to do some blood work and see if you’re lacking in any macronutrients, vitamins, and minerals.

      I would like to suggest you get a solid book on nutrition like Becoming Vegan by Davis and Melina. You’ll get ll the nutritional information you need backed by solid sources.

      Best wishes.

      • Robinparker

        Thanks! I’ve always eaten a mainly whole foods diet, even before I became vegan, so I will look into the blood work. Good idea.

      • BPCveg

        Sounds like great advice!
        Thanks for providing the Canadian dieticians position paper on diet and athletic performance.
        I strongly agree with you that “Becoming Vegan” is a solid book.

        • You’re welcome. Glad the Davis and Melina books are getting around.

          I just want to clarify that the paper is a joint work: Dietitians Of Canada, American College Of Sports Medicine, and American Dietetic Association. So I’d say that’s even better.

    • kk

      Hi, try adding different types of mushrooms.

      • Placing your mushrooms in the sun for 20 – 30 mins before consuming them causes them to produce Vitamin-D like we do. Just a fun tip.

    • Daniel

      Make sure you are getting enough calories. Sounds obvious but sometimes it’s just lack of calories that makes people tired rather than a lack of some particular macro nutrient. 

      • Great point that I should have included. Transitioning to a new diet can cause one to miscalculate calories because of the unfamiliarity of the food and access to it.

    • TiagoCartageno

      Hi Robin. I´m 95% vegan for 5 months ( I´ve been eating eggs and cheese once or twice in a month) and I´ve felt also tired. Then I took a B Vitamin and I felt a big boost of energy in my body, and now I´m taking it everyday.It´s very important for vegans to take the whole B Vitamin complex not only the B12. You´ll notice a big difference. 

  • gz

    Admittedly I’m not sure what the numbers actually mean, but at a quick glance the IGF #s for the people who drank 1/2 a pint of soymilk or more in the chart at 1:15 seems to be more than a borderline increase.   No soymilk had IGF numbers averaging 23.2 and 1/2 a pint or more was in the upper 29s.  That seems pretty significant to me, what am I missing? 

    • Ted


      “Significance” in this sense means “statistically
      significant.” If the P-value shown was
      0.05 or less, then the trend would have been considered significant and the
      results of increased level of IGF-1 due to the additional soymilk.  However, since the P-value is 0.054, the apparent
      trend is not “significant” meaning the increase in IGF-1 can be attributed to
      chance and not the additional intake of soymilk.

    • BPCveg

      In medical research, “significant” has been arbitrarily taken to mean that the difference in an average value (e.g. IGF number) between the two groups being compared (e.g. soydrinkers versus control group) only has a 5% chance (i.e. p=0.05) to have been detected by chance alone (i.e. be a false positive). Often results are only publishable if they cross this arbitrary threshold. This is based on a number of questionable assumptions (i.e. normal distributions, equal variance, etc) , so the trending values (e.g p=0.054) that was rejected as not-significant could really be a real effect that was undetected by a poorly designed study. 

      What often obscures the ability to detect an effect as significant is the amount of variability in the data and the number of people in each group. So a better quality study would control more sources of variability (e.g both groups should exercise the same amount) and use more people. This would then lead to a study having higher “statistical power”, which means it would be more likely to differentiate true differences from those that are due to random effects. Hope this helps.

  • Thinkaboudit

    I’m trying to find the video that states that vegan men had higher levels of testosterone and lower levels of prostate cancer. Could someone direct me to that video? Thanks.


  • Geoffreylevens

    Another question I would ask is what about if some eats an old school, “Diet for a Small Planet” meal that combines different plant protein sources and so ends up with a “high quality” amino acid balance, like beans and whole grains together?

  • Coacervate

    There seems to be a lot of lit focus going back some 50 years on formation of lysinoalanine in soy and dairy protein.  Glycinin and casein (soy and dairy protein, resp) seem somehow primed to the formation of these covalent crosslinks.  I wonder if we are finally seeing a physiological effect of these long-studied modifications.

  • Mary

    What a about isolated pea protein?  I use it in my smoothies and I’m now wondering…if isolated soy protein can have a negative impact on IGF-1 levels, does pea protein have the same issue?

    • Toxins

      There is no dietary need so supplement protein. Not getting “enogh” priotein is more of a marketing fad than truth. All wholep lant foods contain complete protein and protein needs and caloric needs are equivalent. If your eating whole plant foods when your hungry till your full you are getting enough protein.

    • Veganrunner

      Hi Mary,

      There is a convenience aspect. After coming back from a long run it sure is nice to throw a little bit in a blender and be done with it.

  • Toxins

    There is no need to supplement with a B complex, as all b vitamins except b12 is present in plant foods. Eating a starch based diet tends to satiate and provide adequate nutrition as opposed to eating only greens, nuts and fruits.

  • Seanab

    Hi Dr. Gregor, 

    I just watched the series on saturated fat and endotoxins, and wondered if you could comment specifically on plant-based saturated fat, like coconut milk. Is it also associated with increased endotoxins in the blood, or does the fact that it does not include an infusion of dead bacteria lower the endotoxin load? 

    Similar question regarding cheese: is there a lower dead bacterial load, and is there therefore less of an endotoxin load transported with the saturated fat?



  • Malley

    What about if you have organic or non-GMO soy products, does that make a difference?

    • Toxins

      It shouldn’t make any difference as the amino acid structure does not change with organic vs conventional.

  • zohar

    What vegetarian substitutes would you recommend with high protein value? and doesn’t soy contains Estrogen alike enzymes (or hormones)

  • Derrek

    Is Dr. Greger against most supplements like BCAA’s? I know he doesn’t suggest protein and caffeine and gree tea.

  • Paul

    I’m currently on a fruit-based diet, with very minimal amounts of protein. Will adding beans to my diet lower my IGF-1 even further?

    • Geoffrey Levens, L.Ac.

      No idea what adding beans will do to IGF-1 level but if you do add them, and subtract isocaloric amount of fruit, you will reduce your likely high risk of immune dysfunction, systemic fungal infections, and tooth decay from the 80-10-10 super high sugar intake from all that fruit!

  • Mindaugas Raulinaitis

    Totally conused again :( Just after reading this fresh info:

    When IGF-1 levels are too high, some forms of cancer grow more easily (mainly prostate and breast). However, when IGF-1 levels are low, risks of cardiovascular disease, dementia, Alzheimer’s, and sarcopenia are all much higher. In fact, death to cancer is also much more common with low IGF-1 too, possibly due to increased risk of cachexia (muscle wasting).