Doctor's Note

Why might we want low levels of IGF-1 in adulthood? See IGF-1 is a One Stop Cancer Shop. As we saw in How Plant-Based to Lower IGF-1?, vegan men have higher testosterone levels, which can be a risk factor for prostate cancer and enlargement, but given the average IGF-1 levels of those eating plant-based diets this may not be an issue. See Developing an Ex Vivo Cancer Proliferation Bioassay and Prostate Versus a Plant-Based Diet. Having said that, if they eat excess "high quality" protein, they may not retain their IGF-1 advantage. SeeHigher Quality May Mean Higher RiskAnimalistic Plant ProteinsToo Much Soy May Neutralize Plant-Based BenefitsHow Much Soy Is Too Much?, andIf you haven't yet, you can subscribe to my videos for free by clicking here.For more context, check out my associated blog posts: Stool Size and Breast Cancer Risk and Vegan Men: More Testosterone But Less Cancer
  • http://nutritionfacts.org/ Michael Greger M.D.

    Why might we want low levels of IGF-1 in adulthood? See IGF-1 is a One Stop Cancer Shop. As we saw in How Plant-Based to Lower IGF-1?, vegan men have higher testosterone levels, which can be a risk factor for prostate cancer and enlargement, but given the average IGF-1 levels of those eating plant-based diets this may not be an issue. See Developing an Ex Vivo Cancer Proliferation Bioassay and Prostate Versus a Plant-Based Diet. Having said that, if they eat excess “high quality” protein, they may not retain their IGF-1 advantage. See Higher Quality May Mean Higher Risk, Animalistic Plant Proteins, Too Much Soy May Neutralize Plant-Based Benefits, and How Much Soy Is Too Much?.

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

    • HemoDynamic, M.D.

      So what you are concluding is you don’t have to eat the Beef-Steak to be a Beef-Cake! 
      ;-}

  • Mike Quinoa

    I always get a chuckle out of those bunnies.

  • Marc

    What is your take on soy protein isolate as the main ingredient in “fake meat” such as veggie burger? Should we avoid consuming it everyday and aim at eating tempeh and natto instead, or is this unfounded fear?

    • Toxins

      Soy Protein isolate promotes IGF-1 more significantly than cows milk. I would advise staying away from the stuff!
      http://www.ncbi.nlm.nih.gov/pubmed/12629084

      • Chung Gouy

        What about soy protein concentrate. I know it’s not as refined as isolate, but is it best to avoid it too? The soy milk I drink contains soy protein concentrate rather than the soy bean.

        • Toxins

          In general, there is no dietary need to suppement protein as excess is stored as fat. Protein needs and energy needs are equivalent, and if you need more protein, naturally you would consume more food which would provide the protein.

          • Cody

            are you kidding me? excess protein is not stored as fat.. get out of the 50′s and into 2014 please.

          • Toxins

            If protein is not used for energy or functional needs, it is stored as triglycerides. This is true of carbohydrates and lipids. This is basic common nutrition knowledge you would learn in an introductory nutrition course. I am not inventing these facts.

          • Geoffrey Levens
          • Geoffrey Levens
          • Toxins

            No, it is not incorrect. Stored fat can actually serve to store essential fats as well. There is a point of storing too much fat though. We should be on the lower end of our “ideal” weight. It is not healthful for men to dip below 5-3% body fat and for women to dip below 10-8% body fat. Low fat whole foods plant based eating will maintain perfectly healthy body fat percentages.

          • Easy

            Where does the excess calories go, then, Cody? Thin air?

  • Geoffreylevens

    It has been sort of defacto tested in the gym. You have only to look at competitive “natural” body builders and compare them to the anabolic steroid and growth hormone injecting “big dogs” to see the results. Of course, there is that pesky issue of cancer risk.  So I guess it just depends on your goals;  A long healthy life as a more normally endowed person, or get really big and die young and screaming… ;)

    • Bradleyandflynn

      Geoff your post talks about anabolic steroids which we know enhances muscle growth in humans. This article deals only with igf1. I used Igf several times for pedriods of months as a bodybuilder. It had no benefit.

      • GeoffreyLevens
        • GeoffreyLevens

          oops… does not benefit everyone of course.  I had very low free testosterone, symptoms mostly low energy and depression. I tried HCG injections and also topical T cream, went from very low to dangerously off the charts high in blood and saliva tests and experienced zero effects on any level. Maybe, maybe slightly faster beard growth at high levels…  Physiologies differ.  I may be wrong buy someone who claimed to know him when, told me that Ahnold used growth hormone as his juice of choice.

          • JD

            This video is regarding insulin growth factor 1, which is one of many hormones your body produces, but yet is still different then testosterone and HGH that your referring too. The relevance of this video is that IGF-1 is heavily associated with an increase in cancer probability.

        • Mark

          Just because they do it, doesn’t mean that it is helpful. Body-builders do a lot of dumb things, just like everyone else.

          Their increase in muscle mass is most likely attributable to their extreme training, high calorie diets, creatine supplementation, and use of anabolic steroids. The rest is mostly hooey and snake-oil.

  • abeleehane

    Why Michelle Obama ??

  • WholeFoodChomper

    Like Marc below, I’m also interested in hearing what your opinion is regarding isolated soy proteins, specifically TVP. I have just finished reading “The Fat Vegan” chapter in Dr. McDougall’s _The Starch Solution_ and he’s pretty clear about staying away from the stuff: “Removing meat, poultry, fish, shellfish, eggs, and dairy are well recognized dietary changes that lower IGF1 levels. Isolated soy proteins should be added to the top of that list.” What do you think the scientific evidence indicates? Is it safe to eat TVP?

    I can see based on Toxins’s response, that isolated soy proteins are best to be avoided, but what is your professional opinion Dr. Greger?

    • Toxins

      I
      would advise staying away from the
      stuff and i am sure Dr. Greger would agree! soy Protein isolate raises IGF-1 twice as much as does cow milk. http://www.ncbi.nlm.nih.gov/pubmed/12629084

      • WholeFoodChomper

        Thanks, Toxins. Although, I am still curious what Dr. Greger and the current research has to say about it.

        Personally, I’m not that crazy about TVP, but my BF is fond of it as a meat replacement in certain recipes (chili, tacos, spaghetti sauce). I already took away meat and dairy from him, if I take TVP away too, I’m afraid he will give up on the whole plant-based eating plan. Although he has made some tremendous changes to his eating habits, he is not as gung ho about the plant-based eating thing as I am. Is TVP (eaten occasionally) worse than meat? (We use Bob’s Red Mill TVP, not sure if that makes a difference.)

        On a related note, what do others use besides TVP in recipes that usually require ground meat. We’ve tried lentils and tempeh. Again, I like them, but the BF is not keen on those either.

        Just trying to make plant-based eating as yummy and practical as possible. I’m finding that sometimes it just is not that easy.

        • GeoffreyLevens

          Have you tried big chunks of mushrooms, like Portobella? And combine that w/ beans for “ballast” and umami flavor adds like a little miso or nutritional yeast.

          • WholeFoodChomper

            Great ideas, Geoff. Actually, you reminded me that I once made an awesome chili with chopped portabellas as a base. The beauty of TVP is that it is super fast and easy and does not require all the prep time as the shrooms do. But, I do like the idea. Still holding out that may TVP is not that bad,

          • GeoffreyLevens

            TVP highly processed, no nutrients, yada yada. I think not even in same ballpark w/ critter though. Plant protein in concentrated form like that will jack up IGF-1 but also increases IGF-1 binding hormone as well that partially mitigates. Not bad on occasion but if eaten regularly just takes the place of truly beneficial foods. ALL mushrooms apparently have pronounced anti-cancer effects…

      • WholeFoodChomper

        Recently, I have come across a product called Instant Soy Milk Powder made by Now Real Food. I like it b/c I feel it is more versatile than buying soy milk, it provides more bang for the buck, and it conserves space (e.g. storage, camping, emergency prep kit, etc.).

        Any sense what the verdict is on powdered soy milk in terms of isolated soy proteins? The ingredients listed simply state that it is “Non-GMO (Non-Dairy) Soy Milk Powder.” Additional product info states: “Soy Milk Powder is a rich and creamy beverage mix that dissolves easily in water. It is derived from whole, non-genetically engineered soybeans and is a good source of vegetable proteins and Omega-6 fatty acids. … It also typically contains 28 mg of Soy Isoflavones per serving. …”

        What do you think? Use or avoid?

        • Toxins

          It seems perfectly fine to me! Its just dried soymilk judging from the ingredients.

          • WholeFoodChomper

            Thanks for chiming in, Toxins. That is what I suspected. Thank’d for your input on the matter. :)

  • Bataleon

    What is the reason for vegans and vegetarians having higher testosterone levels than meat-eaters? I’ve always thought a diet high in saturated fats promoted an increase in free testosterone levels. Thanks.

    • http://www.DonForresterMD.com/ Don Forrester MD

      I haven’t seen an article addressing that specific question however there are related studies. PCOS (polycystic ovarian syndrome) is a condition affecting up to 5% of women which has elevated testosterone and insulin resistance. It responds well to a whole foods plant based diet(PBD). There testosterone levels functionally go down for three reasons… higher fiber tends to decrease both female and male hormones going out of the body via the intestine due to increased fiber and transit time see… http://nutritionfacts.org/video/food-mass-transit/ and see… http://nutritionfacts.org/video/relieving-yourself-of-excess-estrogen/, the steroid binding hormone in the body goes up with a low fat PBD so more of the active hormone is bound in the blood and not available to tissue, and lastly b/o the lack of meat consumption the amount of artificial male hormones ingested disappears see… http://nutritionfacts.org/video/anabolic-steroids-in-meat/. As a cyclist I’ve always wondered whether as a vegan my testosterone level is lower and if it effects my strength however when you look at the advantages… better arterial health, less cancer, less body fat, less chance of diabetes/back problems/sexual dysfunction/dementia/macular degeneration/kidney stones… the list is long.. in my opinion there is argument against PBD. Of course if the ratio of male to female hormones determines femininity or masculinity sense both hormones are affected my guess there is overall effect. This would support your opinion that a diet higher in saturated fat with less fiber and more meat results in higher testosterone levels with it’s associated increase in Prostate Cancer. Hope this helps.

      • Bataleon

        Thanks for the extremely detailed reply, I found it very informative.

  • Johhny

    No way in hell do vegans have higher testosterone levels. How come there are very few strength athletes who are vegan?

    • Toxins

      I disagree, not that this has any base in science, but a quick google search can find plenty of vegan athletes. I myself am a competitive rock climber and noticed significant strength and endurance gains once I switched.

      http://en.wikipedia.org/wiki/List_of_vegans

      http://www.mnn.com/food/healthy-eating/photos/9-superstar-athletes-who-dont-eat-meat/joe-namath

      • Miguel Berumen

        Some of the “vegetarian” athletes in this list are highly questionable, as the term “vegetarian” does not strictly mean you don’t consume animal flesh, some eat fish and call themselves vegetarians. In light of this I do know of a vegetarian boxer, one of the best a Brazilian by the name Eder Jofre, also Timothy Bradley the current WBO welter champ goes vegetarian the last couple weeks of training before a fight, to help him cut weight. Never the less I don’t know of any vegan strength athlete.

        • Toxins

          Not that it matters..
          Mac Denzig: http://www.ufc.com/news/Mac-Danzig-Diet-The-Truth-About-Vegan

          Robert Cheeke: http://www.veganbodybuilding.com
          I dont know the health of their diet but the point is vegan does not equate to weakness.

        • Thea

          Miguel: Toxins gave you some great links. Here is the information I give out when I get this question. (And now I’m adding Toxin’s links to the list.) Note that the text below includes some links to books that include actual diet advice. I haven’t read the books myself, but they are worth checking out for people who are interested in the subject. Hope this helps.

          ————————-
          (from meatout mondays)
          Vegan Bodybuilders Dominate Texas Competition

          The Plant Built (PlantBuilt.com) team rolled into this year’s drug-free, steroid-free Naturally Fit Super Show competition in Austin, TX, and walked away with more trophies than even they could carry.

          The Plant Built team of 15 vegan bodybuilders competed in seven divisions, taking first place in all but two. They also took several 2nd and 3rd place wins.

          For More Info:
          http://www.plantbuilt.com/

          ———————
          When Robert Cheeke started VeganBodybuilding.com in 2002, being the only vegan athlete he knew of, he may not have imagined that the website would quickly grow to have thousands of members. Robert says, “We’re discovering new vegan athletes all the time, from professional and elite levels… to weekend warriors and everyone in between.”

          For More Info:
          http://www.veganbodybuilding.com/
          —————–
          There was that other guy who just did a world record in weight lifting. “Congratulations to Strongman Patrik Baboumian who yesterday took a ten metre walk carrying more than half a tonne on his shoulders, more than anyone has ever done before. After smashing the world record the Strongman let out a roar of ‘Vegan Power’…” For more info:
          http://www.onegreenplanet.org/news/vegan-strongman-patrik-babaoumain-breaks-world-record/

          —————–
          Here’s another site that I like:
          http://www.greatveganathletes.com/

          I found this story on the above site: “Pat Reeves has set a new world powerlifting record at the WDFPA World Single Lift Championships. The 66 year old lifter, who has been vegan for 46 years, lifted 94 kg to set a record for the under 50.5kg weight class while competing in France in June 2012. The lift was more than 1.85 times her bodyweight, which is exceptional for her division. Pat is now officially the oldest competing weightlifter in Europe.”

          Hope everyone finds this helpful.

          ————————-

          SJS (Guest):

          Jason, Robert Cheeke, a vegan bodybuilder has a book on Vegan bodybuilding. It has gotten good reviews on Amazon. https://mail.google.com/mail/u/0/?shva=1#inbox/1441cb65c23e6217

          11:51 a.m., Monday Feb. 10
          ————————–

          For those who want a more thorough dietary guide, I suggest Thrive: The Vegan Nutrition Guide to Optimal Performance in Sports and Life by Brendan Brazier. His book is exclusively about vegan sports nutrition and contains a variety of great tasting recipes along with a 12-week daily meal plan.
          (someone on Amazon)

  • Elizabeth

    Usually, the captions on these videos are spot-on. But “millews” for “milieus”? Please correct!

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

      fixed!

  • Name

    Dr. Greger, I was wondering about how lower IGF-1 levels in vegans might affect their height?

    • Geoffrey Levens

      A trip to India might tell you. I am a 5’3″ man and I was one of the very tallest people on the street in New Delhi. Only people taller were other Westerners and the rare, obese, super well dressed, and obviously rich Indains

      • Name

        Well the only thing that makes me suspicious about drawing conclusions from all of these nations where the people have a vegan or primarily vegan diet, is that I have done some research that claims the height can arise from genetics, as well as if a person is receiving enough food (now whether or not these studies went off of correlation and did not test actual causation, I do not know). Even if a person receives enough nutrition to survive, if they do not have access to adequate amounts of nourishment, their body will not grow beyond the limits at which said person could acquire the necessary amount of food.

        • DanielFaster

          Yet Americans have been shrinking. http://www.theguardian.com/world/2004/apr/04/usa

        • emjayay

          From what I know, height is far more nutrition based than heredity. Netherlands men are now on average the tallest, and hundreds of years ago (there are some kind of records, besides all the short little suits of armor from the Middle Ages)were far shorter. The baby boom generation is taller than their parents. 6 feet tall Asians were rare and for their kids in the US common. Fifteen years ago I stood at the head of a line of a Japanese retired people group and could see over the top of every head, and I’m 5’10. Even given a little shrinkage, they were definitely all really short.
          Mexican families in the US are typically very short and fat (just observation) with short fat kids, who they no doubt feed the same way. We’ll see how tall the kids get – they will start eating some vegetables and protein besides beans with the new school lunch criteria. Maybe once they get into school they will catch up in a few years.
          I don’t know if anyone has figured out entirely what nutritional components have the biggest effects on this, or if it’s IGF or what.

  • oliver

    you missed the whole point bb’ers eat meat protein.it’s nothing to do with igf, it’s the completeness of the protein. if I want 200g a day of complete protein, it’s easy with animal sources as all the protein is complete. with non animals, you have to mix and match complementary foods to get the full amino acid profiles, it’s very messy and not very precise. if you look at vegan vs normal bber’s, you’ll see a big difference in muscularity.

    • Geoffrey Levens

      But that is the point. The reason “complete protein” is so effective and desire by body builders is that it stimulates IGF-1 release which in turn stimulates rapid muscle growth. Oh and by the way rapid cancer growth. The real point is that “getting big” and being super healthy and living a long time may well be incompatible goals

    • Toxins

      I will share what Jeff Novick has shared regarding this issue.

      Firstly, I would like to quote the American Dietetics Association on their view of vegetarian diets and protein.

      “Plant protein can meet protein requirements when a variety of plant foods is consumed and energy needs are met. Research indicates that an assortment of plant foods eaten over the course of a day can provide all essential amino acids and ensure adequate nitrogen retention and use in healthy adults; thus, complementary proteins do not need to be consumed at the same meal ”

      http://www.vrg.org/nutrition/2009_ADA_position_paper.pdf

      Many say that plants foods are incomplete

      If “incomplete” means not containing all the essential amino acids then…. (the incomplete protein theory)

      1) All plant foods are complete as they contain all the essential amino acids.

      2) the only food that is not a complete protein is an animal food, gelatin.

      If “incomplete” means lacking in sufficient quantity of one or more amino acids…(the limiting amino acid theory)

      1) Getting all the amino acids in at once at the same meal, or even in the same day, as some may suggest, is not necessary due to the amino acid pool, which is a circulating level of amino acids in the blood, that the body can draw from if needed. As long as one follows a whole foods plant based diet, the amino acid pool will maintain a sufficient stock of any potentially needed (or limiting) amino acids.

      2) However, as long as one consumes enough calories, eats a variety of food, and limits junk foods and refined foods, and is not an all fruit diet, then they will get in enough protein and enough amino acids in sufficient quantity. There will be no limiting amino acids

      3) there is some evidence that the amino acids that are slightly lower (but adequate) in plant foods, may actually be a benefit to health and longevity and not a concern. This evidence stems from the fact that eating foods that resemble the protein structure of humans causes the liver to release excess amounts of the growth hormone, IGF-1, which accelerates aging and promotes tumor growth. (https://www.facebook.com/notes/rami-najjar/igf-1-and-cancer-growth/10151343380800828)

      Most every major health organization including the NAS, the WHO and the ADA all recognize these statements to be true.

  • Derrek

    Is 40/40/20 bad for body? In other words is that much protein harmful? I’m trying to gain muscle but as healthy as possible. I heard 80/10/10 is effective but hope this doesn’t hurt my gains. Thanks!

    • Isaac

      Definitely don’t do 80-10-10. Fruitarianism is not sustainable. It’s a fantasy, I’ve tried it, and it does not work. Protein and healthy fats are good for gaining. I eat about 33/33/33, as I believe carbs simply turn to glucose and don’t store (or only store as adipose(fat tissue)), while proteins/healthy fats go directly to body composition.Eat nuts, seeds, avocados, salads, mung bean soup, sweet potatoes with grass fed butter, and make sure to get vit. D3 and plenty omega-3′s. I eat eggs and salmon occasionally too. They may have toxins, but considering we’re eating a very healthy diet, a small amount of eggs/salmon will help muscle mass with a small expenditure of toxins. In other words, high protein and high (healthy fats, avocado, grassfed butter, coconut oil (we need some saturated fats) and omega 3s in flax, walnuts, and oily fish are great sources of nutrient dense foods.

      • Toxins

        Glucose does store actually in the form of glycogen in the liver and muscles. Proteins have no storage mechanism and are used on an as needed basis. If we consume excess protein, it is stored as fat tissue.

        The emphasis of diet on this website is to consume a low fat diet.

      • Dan

        Grass fed butter? I would be interested to visit a butter ranch, never seen butter in its natural habitat before lol

  • Harry

    Convenient that you would hand-pick studies that state the hypothesis you support: IGF-1 has no effect on muscle mass. Too bad other studies say otherwise. The pioneering GH study done in 1990 I believe, took about 25 60-year old dudes and gave them GH. The result? It seemed they turned back the clock 10-20 years in terms of muscle and bone mass.
    The conclusion? You’re biased. Big surprise. Vegan queers!!!! hahahahahahahahah++++++++

    • Toxins

      Do you have the study link on hand or is that a 3rd hand account of the study?

    • http://www.DonForresterMD.com/ Don Forrester MD

      I would also appreciate the reference to the study you cite.

    • Geoffrey Levens, L.Ac.

      Vegan queer here and proud of it! I do remember that study though I don’t have links etc. They also (the GH group) showed up with increased arthritis, diabetes, and a host of other problems in a fairly short time frame. I do agree, that GH has effect on muscle mass/growth. The real question in my mind is do you want to be a great big, macho man and die young and screaming, or a scrawn-dog, veiny, plantarian and live a very long and healthy life? Perhaps you get quite a bit of choice in the matter. Pass the broccoli please?

      • Toxins

        Not to say that people eating plant based cannot gain muscle mass and be competitive athletes! I myself am a competitive rock climber and have developed strength faster then pre vegan, although anecdotal.

        • Geoffrey Levens, L.Ac.

          YOu betcha! Quite a few prof. athletes reporting faster recovery, better endurance, able to train longer and harder etc. But for some “size” REALLY matters ;) Being “bulked” I would think not such a good thing for rock climbing. You want functional muscle, go not show. Don’t know how GH effects that variable but personally, old surfer/snowboarder/martial arts for fun kinda guy, fo me it doesn’t really matter. Being the strongerst, fastest, toughest kid on the block sort of wears a bit thin when you show up w/ a cancer diagnosis, eh?

          • Toxins

            True indeed, that is why body builders can never climb well. Its heavy muscle with no real use other then for show!

          • DanielFaster

            Works for bike racing too, at least climbing and sprinting! Stick to ‘Italian weigthlifting’ [pedaling in a hard gear].

          • Geoffrey Levens, L.Ac,

            Just be sure to keep RPM’s high or you can easily blow a knee.

          • Thea

            Geoffrey: Nice post!

            For fun, ya gotta check out the following story/picture. This vegan record-breaker body builder has some serious bulk. :-)

            http://www.thestar.com/news/gta/2013/09/08/vegan_strongman_shoulders_550_kg_a_record_perhaps_at_vegetarian_food_fest.html

          • Geoffrey Levens, L.Ac.

            One word, “WOW!!!”

        • Eisenhorn

          Check out Nick Diaz MMA fighter… Also VEGAN!

  • Guest

    Dear Dr. Greger,

    http://www.proventivenutritional.com/harmonized-protein-2/ is a whey protein that reports to “promote the release of growth hormone.” Considering your stance on IGF-1, would it be reasonable to say that we want to avoid the release of growth hormone, such as through consumption of a product like tihs?

    • Toxins

      Precisely, all supplemental proteins should be eliminated. There is no dietary need to consume supplemented protein.

  • mickus

    I’ve read somewhere that Vegan diet can lower IGF 1 whilst raising HGH, anyone know if this is true? Also, does HGH have similar side effects to IGF 1?

  • Miguel Berumen

    I was a vegetarian for 3 years and a vegan for 2, I supplemented my diet with everything possible from nuts, seeds, whole grains, algae, pseudo-grains, chlorella etc. Always have been an athletic person with more emphasis on full contact sports (boxing, muay thai, etc.) and never have I felt so weak and had muscle lost and over all body mass lost as when I was a vegetarian and more so a vegan. This is something I have observed with other vegan-vegetarians, I met some “vegan” body builders they looked good but later I came to find out they where being “assisted”. I am interested in opinions if possible from vegan athletes if possible from full contact sports in their personal experiences, as this is my personal experience and though research and studies are good and always shed some light, most don’t convert to real life with all it’s variants, thank you.

  • Zaz Zaz

    If you work your muscles hard enough /often enough, rest enough, sleep enough, & consume enough calories, you’ll get enough protein to build as much muscle as your genetics allow. Diet should focus on supplying fuel to burn at workouts,(carbs).

  • Craig

    Dear Dr. Greger, I want to be a plant based bodybuilder, but my energy levels are much less and recovery periods 3 times longer after heavy exercise when I remove fish and protein shakes from my diet. I’m 50 yo, and slim, I eat a can of sardines twice a week and 31 gm of whey protein isolate daily and have tons of energy and better recovery than if I only eat my beans, brown rice, nuts, and fruit and vegetable shakes and vitamin supplements. I don’t eat sugary or salty or processed food either. I don’t want to die of cancer but I also can’t afford to sit around doing nothing all day. What am I doing wrong?

  • Larry Taylor

    Dr Gregor. I have a related question. I am a 100% high carb vegan. Presumably i have lower serum IGF-1 levels than the meat & dairy eating population. If i switch from endurance exercise to weight training am i likely to weaken that advantage? Do vegan bodybuilders have higher serum IGF-1 than vegans in general?