You probably heard about insulin before.
It’s the hormone that’s released when you eat those tasty carbohydrates and that makes you fat. At least, that is what all your diet books have told you right?
But if insulin is so bad for your physique, then why do bodybuilders inject insulin?
Well I’m glad you asked.
Insulin 101
One of the main functions of insulin is too keep your blood sugar under control. Your body can become resistant to insulin and this results in diabetes.
In recent years, insulin has gotten a bad name as ‘’the evil storage hormone’’.
Insulin is demonised as a hormone that stores the food you eat as body fat and prevents your body from using body fat as a fuel. This is principle where most low carb diets are based upon: eating less carbs results in less insulin release, which results in less body fat.
While that sounds nice in theory, things are nowhere near as simple as that. A topic I’m sure I’ll be talking a lot about in the future.
So a lot of people are afraid of insulin because they think it’s bad for their health and weight. Yet many dedicated gym rats intentionally try to increase insulin levels through food strategies or even injections because they think it will help them build muscle mass.
But are they right or wrong?
Insulin and building muscle
Chances are if you have the guts to read one of my research reviews, you’ve been reading about fitness for a while. In that case, I’m wondering what you currently believe the effect of insulin is on building muscle? Is it extremely effectively, totally useless, somewhere in between?
Second question: how sure are you of your answer?
Because not all scientists agree with each other on this question. Simply because there’s quite a few studies saying it’s working, but just as many who say it does nothing.
And that’s why I conducted a systematic review on this topic.
Specifically, we looked at the effect of injected insulin, rather than insulin release in the body in response to food.
We did this because eating does not only results in insulin release, but also provides energy and provides nutrients that turn on all kind of processes in the body. This makes it really hard to say if it’s the insulin that is causing the muscle growth or one of these other effects of food.
How does insulin affect muscle protein synthesis?
Before we go to the juicy results of the review, it’s important to know some background information to make sense of it all.
We muscle physiologist often measure a process called muscle protein synthesis. It’s the process of building new muscle tissue.
There’s two ways how insulin is thought to influence muscle protein synthesis:
The first is that insulin directly stimulates the cellular pathway in the muscle that regulates muscle growth. Basically, it goes to a muscle cell and turns its muscle building machines up a few notches.
The second is that insulin increases blood flow to the muscle. Thereby, more nutrients, hormones and the like can get into the muscle which can stimulate muscle protein synthesis and provide the building blocks for growth.
The effect of insulin in combination with high doses of amino acids
After I indexed the whole scientific literature, I found the results where a coin flip. About half of the studies reported that insulin increased muscle protein synthesis, while the other half reported that insulin had no effect.
So I started to look if there were differences in the studies that might explain the different results.
A lot of studies didn’t just inject insulin, but also injected high doses of amino acids (the building blocks of protein and muscle).
All these studies found that the combination of insulin and a high dose of amino acids increased muscle protein synthesis. However, these studies cannot conclude that insulin stimulates muscle growth, because infusion of high doses of amino acids can stimulate muscle growth on their own.
So the question then becomes: can combination of insulin and amino acids stimulate muscle protein synthesis more than amino acids do on their own?
And that is exactly what was investigated in a very nice study. In this study four groups of subjects where infused with a high dose of amino acids. All four groups received insulin as well, but all four at a different dose from very low to very high. And no matter what dose of insulin was infused, muscle protein synthesis was equal in all groups.
So the first conclusions from my review are of my review is:
The effect of insulin on amino acids
Of course, there are also a lot of other studies that infused insulin without infusing amino acids.
There’s one problem with that though.
Insulin lowers the amount of amino acids in the blood. And since amino acids stimulate muscle protein synthesis, these studies basically shoots themselves in the foot.
So to no surprise, insulin did not stimulate muscle protein synthesis in any of the studies in which it lowered the amount of amino acids in the blood.
Therefore, the second conclusion of the review was:
What is the effect of the insulin dosage?
An obvious difference between all the studies was the dose of insulin infused.
The dose actually didn’t seem to matter much, except when extremely high doses were injected that increased the amount of insulin in the body to levels that the body cannot produce itself. We call this supraphysiological levels.
These supraphysiological doses have not been studied a lot, partly because they are very dangerous. But in all those studies, insulin did increase muscle protein synthesis.
Therefore, the third conclusion of the review was:
Does age play a role in the effect of insulin?
The 3 previous categories provided pretty clear conclusions as to when insulin works and when it doesn’t. But we’re were still left with a lot of studies that not fall in the previous catogories and reported different results.
All of the remaining studies solved the problem of amino acids dropping in response to the insulin infusion in one of two ways.
The first option is to infuse a small amount of amino acids to keep the amino acids at normal levels (not high enough to stimulate muscle protein synthesis on their own).
The second option is to infuse insulin only locally in a muscle. For example, infuse insulin only into the circulation of one leg. That way, the insulin has no effect in the rest of the body and the blood continually delivers the leg with fresh blood that has normal levels of amino acids.
The last step we did was to separate the studies based on age of the subjects.
We did this because there is some indication that the elderly are less responsive to the effects of insulin.
We found that 3 studies found no increase in muscle protein synthesis in the elderly, but one study did. Interestingly, that study used the highest dose of insulin of all four studies.
Therefore, our fourth conclusion was:
So does it work or not?
So in the end, we took these 4 factors into account:
– whether amino acids were being infused at high doses along the insulin
– whether amino acids in the blood dropped
– whether the concentration of insulin in the blood was normal or supraphysiological
– whether the subjects where young or old
This allowed us the get the best possible picture of what insulin does without a lot of other variables that might influence the results.
Despite that, it still wasn’t entirely clear what the effect of insulin was.
We were left with 21 studies, of which 8 concluded that insulin improved muscle growth, but 13 concluded it did not.
Therefore our fifth conclusion was:
Practical Implications
So how can we apply what we’ve learned.
Let’s go back to the bodybuilders who inject insulin. They inject insulin at incredibly high doses that cannot be produced in our body naturally, and yes that approach seems to be effective to increase muscle protein synthesis. Warning: it’s extremely dangerous and NOT recommended.
So what about regular fitness people who use dietary approches to manipulate circulating insulin levels?
In the fitness world it’s common advice to eat carbohydrates after resistance training to stimulate insulin production which is supposed to stimulate muscle growth.
However, the majority of the scientific literature suggests that it won’t help.
It’s much more important to get your protein after resistance training.
A protein shake or meal provides you with the amino acids needed to stimulate muscle protein synthesis. And as my review pointed out, there’s not a single study that shows that insulin has any benefit for muscle protein synthesis when you have enough amino acids in your blood, which is the case if you drank your protein shake.
In line with these insulin injection studies, the addition of carbohydrates to protein also has no effect of muscle protein synthesis (1).
What about muscle breakdown?
Now some of you will scream: but muscle protein synthesis is only one side of the coin! What about muscle protein breakdown? I’ve heard insulin slows down muscle protein breakdown!?
Indeed, it’s pretty well established that insulin reduces muscle protein breakdown.
However, this effect occurs at low levels of insulin with no further effects at higher levels. Eating a decent protein meal will already increase insulin levels high enough for the maximal effect (2).
What about muscle glycogen?
So carbohydrates and insulin are not directly helping you to build muscle.
But what about carbohydrates to recover muscle glycogen (storage form of carbohydrates in the muscle), which in theory could help increase training volume?
Muscle glycogen repletion is one of the most important factors in recovery from endurance-type exercise.
However, resistance training with moderate volume (6-9 sets) only depletes ~36-39% muscle glycogen (3) (4) (5). While some athletes have considerable larger training volumes, it usually comes at the expensive at training frequency. For example, body part splits train muscles with very high volume, but only train each muscle group once or twice a week.
Ironically, unless you’re on a low carb diet, muscle glycogen should always be replenished between resistance training sessions for the same muscle group.
However, don’t mistake this as a ”avoid carbohydrates” message. Carbs are absolutely fine, and if they fit your macronutrient plan, you might as well have some surrounding your training.
Now here’s what I want you to do…
I would love to hear from people who heard that it’s essential to eat carbohydrates after resistance-training ASAP because the insulin release is crucial for optimising the growth response in this ”anabolic window”.
Leave a comment.
Great article. I came here looking for research on the topic of the relationship between carbohydrates and anabolism. I’ve noted that when I’m on a low carb diet, esp when intermittent fasting, I seem to lose considerable muscle mass. It’s not just fat it’s definitely muscle that’s being lost. I know as I’m an ectomorph with a fairly high metabolism. I decided to reduce carbs as I found out I was prediabetic. I feel much better now but the only downside is less muscle. I’m also consuming the same account of protein. Maybe the solution is to increase my protein and keep the carbs low in order to regain my size. Long story short, in my experience carbs and insulin definitely do seem to be anabolic.
Hey Darren,
Thank you for the nice words and sharing your experience.
Keep in mind that carbohydrates and insulin are not the same thing. Insulin release, is only one of the metabolic effects of carbohydrates. So carbohydrates may be anabolic, but that does not mean insulin is. The anabolic (and/or anti-catabolic) effects of carbs may be mediated via the energy in carbs, effects of glycogen etc.
Kind regards,
Jorn
I’m a Type 1 diabetic, insulin dependent. Downside to taking insulin is weight gain, at least in diabetics, because it normalized but also changes metabolism. HGH is optimal when fasting, but type 1 diabetics find it hard to fast while adjusting insulin. The upside is I put on muscle mass very fast, but this to me is a downside as I put on muscle mass almost faster than I put on strength. But in the plus side working out, especially lifting weights, uses up glucose so a diabetic needs insulin, but the downside is that the muscle uptake of the sugars can happen hours from when you worked out, so your blood sugar can plummet while you sleep.
Basically it is complicated even for a diabetic, so non-diabetics should be wary of trying to increase artificially what you can do naturally.
Yes, type 1 diabetics are continiously tracking their carbohydrate intake, glucose levels, and insulin levels, and it’s still quite hard to keep everything in the healthy range.
Bodybuilders don’t have that experience, and often use much higher doses of insulin, making it quite dangerous.
Interesting to hear, I’m also type 1 since age 12 , 37 now and over the past 2-3 months have been hitting a weight training program pretty hard in an effort to gain muscle mass and weight . I have always been super slim and very high metabolism. 6′ 4” 177.8 pounds last checked . It seems for me in my experience so far that my body is requiring much much more insulin on a daily basis of regular and an increase in 24 hour insulin as well . It is true that i eat more while training but not to the level i have been taking , it’s almost like as soon as i take fast acting insulin it gets used up by my muscles leaving me needing more ? IDK kinda weird You would think it would be opposite . Also i do take creatine and BCAA’s along with Protein for muscle gain . Mabye that could have something to do with the level of inulin needs , and yes i monitor levels like 8-10 times daily during this time . Cheers 🙂
So I am probably coming from a different place from most of your commenters, I am diabetic, I now work on a pump but for years I used syringes to inject insulin, primarily into my thighs, which were huge, all my diabetic friends have noted the same thing, wherever the injection site was, muscles were large and dense and stronger than their peers. Not a statistical sample to be sure, but the pattern was common enough that when you’d talk to an endocrinologist about it they all were familiar with it and said yes it was a thing they’d noticed and recommended rotating injection sites because insulin has a different rate of action when injected into muscle vs fat. Also doesnt insulin lower amino acid levels because it makes the surrounding cells absorb them? Isnt that why you want them in your bloodstream in the first place?
Hey Doug,
Thank you for sharing your experience. If insulin is disproportionately increased in a local compartment (e.g. thighs), it can indeed stimulate muscle protein synthesis in that compartment. This happens, because the local increase in insulin results in increased vasodilation and increased blood flow in that compartment. The muscle of that compartment can then take up more amino acids. But realize this is at the expense of amino acids availability elsewhere, you’re not increasing whole-body anabolism, you are just shifting more of it to the injected compartment.
When insulin is systemically elevated, it does not lower amino acid levels by making cells absorb those amino acids. It does so mainly by making cells release fewer amino acids.
Great article, thank you for your reseaches.
I have been following no carbs diet. I m at my physical best..had followed normal bodybuilding approach all these years with not so favorable results in the area of fat loss specially. We don’t need to refill glycogen tank. Good we eat after work out takes 12 hrs to digest n go to the cells.. so all the anabolic wi Dow is a myth. It’s all about protien synthesis which is activated by m-tor which is activated by insulin which u get from protien sources or incidental carbs that u mite get from other fat n protien sources. One tea spoon of sugar is enuf to have desired level of insulin to activate mTor. We don’t need to consume extra carbs to get insulin spike. Insulin and growth hormone work in opp ways. When u have insulin in blood then Growth hormone is shut and then vice versa. Also workout in fasted state as igf 1 levels are highest if ur fasting close to 15 hrs. Also there is always a danger of insulin resistance when u over eat carbs. So stick to 0.5 gm per pound of bodyweight of protien n high fats n v low carbs. U ha e much more benifits than just fat loss.
If we eat 5 egg whites after intense resistance session of about 60-95 mins. If yes then how will our body fill its glycogen stores. I mean if we continue this post workout for about a month or so our body glycogen stores will deplete slowly and we will be dying to eat carbs what should you do now ….???
Second thing we cannot replace carb from protein because —
1- protein is expensive than carb.
2- carbohydrate is primary source of energy.
3- protein will not fill up glycogen stores of liver and muscles.
And last thing I want you to please study that can insulin along with growth hormone and testosterone increase muscle protein synthesis or one of them can do it on its own.
And it would be great if you can suggest me some good certifications.( nutritionist/ trainer).That i can do to improve my knowledge
Thank you ……..
First part: without eating carbohydrates you won’t replete glycation levels. My post does not suggest you should not eat carbs (either post-exercise or any other time), it’s just saying that carb/insulin do not directly stimulate muscle growth.
Second part: my answer at the first part also covers this. I do not recommend to avoid carbs.
Third part: Unfortunately, I can’t just study what I want. It depends on what you can write a successful grant on, and performance-enhancing drugs in athletes is not a topic that many institutes care a lot about.
Four part: This is a good online course on sports nutrition: https://www.sportsoracle.com/nutrition/home/
Carbs are to b replaced with fat not protiens. Fat us a better source of energy than carbs. Heart works well from the energy from ketones as compared to Energy from Glucose. Carbs are non essential macros. They have no exclusive function. Insulin has more adverse effects than good ones bcoz it’s easy to go over board with insulin as carbs are everywhere around us. Which is y people don’t loose weight
Ketones limit VO2 max to about 70%… without glycogen you can NEVER perform at maximum capacity. Your red blood cells and some brain cells require glucose/glycogen and can not fuel at all with ketones. When you approach zero dietary carbs, your body just converts protein to fill the gap…
Hi Jorn,
Great read, I have a few questions for someone who is skinny fat working to build muscle and lose fat but not looking to lose weight. I’ve read a bunch of studies stating that the less insulin spikes you have the less fat you will have. I’m curious how this then works for muscle building and if switching to a low carb high fat high protein diet is recommended based on the effects of carbs and insulin not being a large factor in muscle building.
Thanks!
Joe
Hey Joe,
Insulin is often considered the bad guy that makes you fat, and it’s therefore often stated you should eat low carb. In short, that if just incorrect.
A high protein diet is beneficial for body composition, but the CHO:fat ratio of the diet is not an important factor for body composition.
Excellent article and dialogue in the comments. I always feel enlightened when I learn something that debunks gym dogma. Thanks again, Ryan.
Thank you for kind words Ryan!
Hey Jorn, I was wondering if you could give me some direction on how this would work with intermittent fasting. Thanks.
In short: I wouldn’t worry much about insulin with regards to body composition.
Theoretically, insulin would be at fasting levels during part of your non-eating window (keep in mind that a 16 hour ‘fast’ doesn’t mean your actually fasted for 16 hours, you’ll likely still be digesting food for many hours). Those low insulin levels may allow muscle protein breakdown to be slightly elevated. It could theoretically also lower muscle protein synthesis rates a bit, but that shouldn’t be much of a concern as MPS can’t really be elevated much in a fasted state anyway.
Hi Jorn will you also compare whey isolate and concentrate sometime?
i was just buying isolate but can not help wonder if its worth the extra cost. unless im (somewhat) lactose intolerant which i do not know
Thanks for the great articles and videos
Hi Alexander,
We don’t have that exact comparison plannend. But we have some new data that is relevant to that question. Be on the look out 😉
Regards,
Jorn
Hi Jorn,
Interesting article indeed. What about insulin (carb intake) to promote better Creatine uptake for muscle hypertrophy?
What’s your take on this one? When Cr is used, then carb become important for hypertrophy?
Thanks!
Hi Durrah,
Insulin indeed promotes better creatine uptake. However, this has little practical benefit. It is relatively easy to saturate your muscle creatine levels (having the maximal amount of creatine in your muscle). If you don’t have reached your maximal creatine levels, insulin can help you get there a bit faster. But once your levels are maximal, insulin has no additional effect. Even without insulin, after a couple of days of loading you reach maximal creatine levels.
Hi Jorn
One thing I’m interested in which will never likely be studied is the effects insulin has on Mtor in bodybuilders.
There’s the recent ‘train low’ studies showing that low carb training can augment better training adaptions in terms of mitochondrial biogenesis and adaption to exercise factors which are essentially eliminated in a high carb training environment. I think James Morton is one of the principal guys on this.
My question is since insulin can have an effect on Mtor would injecting insulin around workout or having a lot of carbs around workout serve a similar limiting effect on the adaption to hypertrophy training stimulus?
I’m studying on the ISSN diploma so have seen the information on train low and also the limiting effect antioxidants around workout can have so logically there may be a similar limiting effect on Mtor response and possibly degree of adaption (muscle growth) by making the training environment insulin rich?
I’m an assisted bodybuilder so interesting for me the effects of exogenous insulin.
Thanks for your time. Good article.
Hi Tom.
It doesn’t seem likely that insulin will be studied directly in bodybuilders (not a population the government is all that interested in). But there’s no reason to assume that the physiology of insulin is different in bodybuilders.
With regards to ‘train low’, this concept is specifically developed for endurance exercise. Carbohydrates/insulin may have detrimental effects on endurance training adaptations. Carbohydrates/insulin have never shown any negative effect on anabolic pathways (e.g. mTOR). In fact, quite the opposite, sometimes they appear to stimulate anabolic pathways. However, as discussed in this article, once you consume sufficient protein, additional carbohydrates or insulin (at physiological doses) has no additive effect.
Do you have to worry about possible detrimental effects of carbs or insulin on hypertrophy:
– No.
Can injecting insulin increase muscle mass in bodybuilders?
– Yes. Because the doses bodybuilders use have been shown effective in studies.
Hi Jorn
Thanks for that reply. I’ve a concern that using insulin pre and post workout may be detrimental in terms of effects on the liver glucose output maybe leading to insulin resistance.
Because of that I generally would only use in small amounts with meals.
Hypothetically of course what would you think to be the best way to use it?
Do you think there’s any benefit to using insulin pre or post workout with carbs or would it not make a difference due to training stimulus on Mtor.
In your study in 2015 I think it was concluded that exogenous insulin does not increase MPS. If this is the case why does it increase muscle mass in bodybuilders?
In my 2015 review I concluded that a physiological amount of exogenous insulin does not stimulate MPS (infusing an amount on insulin that you could achieve if you ate a large meal).
However, a few studies investigated the effect of infusing SUPER high doses of insulin, MUCH higher than what you can achieve by eating. And in those studies, exogenous insulin did work. Bodybuilders inject those super high doses. So it all depends on the dose.
If I would have to speculate, I would guess that insulin can further increase MPS* compared to exercise alone. This is just based on the fact that in the bodybuilding world, they typically claim that insulin (in those insane high doses) is super effective.
*I don’t like to talk about mTOR or other molecular markers of anabolism. They often don’t translate to muscle protein synthesis of muscle mass gains.
That’s great info thanks. Are those studies available open access on pubmed? It’s a topic I’m really interested in.
Plus would be good to see a study on insulin where steroids were also not a mitigating factor.
Thanks for the info.
Hi Jorn
That’s really interesting thank you.
Are the super dose studies open access? I’d like to look at them.
Where they done in the absence of steroids as this would obviously distort any anecdotal doses used by bodybuilders of insulin.
Thanks for your time. Very informative
I think this one is open access? Done in the absence of steroids.
http://www.ncbi.nlm.nih.gov/pubmed/9611157
Thanks F.A.T.
Paleo works fine for building muscle as it has lots of protein. The lower amount of carbs in the paleo diet is not really a problem for building muscle as discussed above.
However, as the paleo diet does not allow processed foods, you’re left with natural foods that generally are lower in energy density. That is great when you’re trying to lose weight, but may be a problem for some if you’re trying to gain muscle. Energy intake is an important factor to build muscle.
As long as you can get your calories in, paleo is fine. But for ectomorphs that have trouble gaining weight and have a small appetite, it may be difficult to consume enough calories while on the paleo diet.
Hi Jorn,
Nice article with a lovely writing style. Base upon your article I was wondering about your opinion on the paleo diet for optimal muscle building since the paleo diet often contains less carbo’s and a lot of proteins and fats compared to a ‘normal’ diet.
I really appreciate this dialogue. As a Personal trainer and Fitness Nutrition Specialist this one area of carbs verses protein has been a big issue for me…issue meaning a topic of continued attempts of understanding.
First, the 20grms of protein post workout doesn’t fit everone of course while genetics, sex and size play the major role. Since both protein and carbs provide same levels of energy i don’t see the added benefit of just using protein to replace energy. One’s total energy balance can be set off as easy with protein as with carbs…
Second, Jeanemarie makes a good point about “What is a workout?” The comment i have is that anaerobic workouts should be considered major depletion of glycogen stores rather than just assuming aerobic workouts do that…they primarily use oxidation cycle of fat stores anyway. After an hour or more intense weight training workout one’s sugar is very low and that is typical of someone trying to build muscle.
This is of real interest to me because many in fitness industry believe carbs are evil for reducing body fat and producing lean muscle. I am NOT an RD as Jeannemarie but nothing in my nutrition studies has proven that to be the case…in fact just the opposite. I’m very interested in understanding more! Thanks for this discussion!
Hi Bruce,
You’re absolutely right that general ”optimal” recommendation still need tailoring for individual needs. With regards to protein intake. 20 gram of protein has the maximal effect for someone of around ~80 kg. However, exact dosing might depend on lean body mass. So if you’re much heavier you probably need a bit more, same if if you’re 80 kg at 5% bodyfat compared to 20% bodyfat. Women generally tend to have less LBM as men at a given weight, so they might need slightly less.
I’m absolutely with you that carbs are not evil. Taking carbs before, during and after a workout is absolutely fine. However, many articles recommend that you MUST take them ASAP post workout in a specific dextrose:maltodextrin ratio to make optimal use of the post workout anabolic window (or something like that). And some designer supplements are marketed as awsome insulin booster for the sole purpose of increasing MPS.
The point I’m trying to get across is that carbs are not needed to optimally stimulate MPS or inhibit MPB. That doesn’t mean you should avoid them. If people are designing nutrition plans, they shouldn’t think adding 50 grams of sugar post workout is mandatory as they are told by many.
Hi,
Can you tell me what you mean by “workout” and does it even matter? My understanding is also that following an endurance or aerobic workout, you want to have protein and carbs as the protein will stop muscle breakdown and help resynthesize muscle, the carbs is not so much for muscle as it is to replace glycogen. I can see where carbs are not required following a mostly strength-training workout but to just say “workout” is a little generalized and I think it would matter the goal and type of exercise.
All that said – your article is great. Just asking for a little clarification. Thanks!
Hi Jeannemarie,
With ”workout” I mean resistance-type exercise. Indeed, carbs might still be required for different outcomes such as glycogen recovery. I’ll edit some parts of the post to make this more clear. Thanks!
Thanks Bruce.
Twenty grams of high quality (rapid digesting, leucine rich) protein is enough to maximally stimulate MPS (1,2). Whey protein is the best, other animal sources are good as well.
Is some of the protein you ingest oxidized for fuel? Absolutely. Luckily, that’s not a big deal. Because despite that some of a 20 gram protein bolus might get oxidized, it’s still enough to optimally stimulate muscle protein synthesis. So you don’t need to ”protect” your protein with carbs. Perhaps adding carbs to a sub-optimal amount of protein can be beneficial for the reason you describe, but in that case it would be better to simply eat more protein instead
My review focused on exogenous insulin, but in my blog I reference the 2 most current studies with the best methodology who investigated whether adding carbs to protein was beneficial for MPS. Both found that adding carbs to protein did not increase MPS (3,4).
So am I saying you shouldn’t eat carbs post workout? Nope. When their caloric load fits in your overall food plan, you might as well take some. However, you should not take unnecessary carbs post workout because you think they are helping you build muscle when you are dieting if you can’t afford those calories. .
Carbs might still be beneficial for the recovery of liver and muscle glycogen stores as you indicate. That mostly applies to endurance-type exercise/concurrent-type exercise, because resistance-type exercise is not that glycogen depleting.
1) http://www.ncbi.nlm.nih.gov/pubmed/19056590
2) http://www.ncbi.nlm.nih.gov/pubmed/24257722
3) http://www.ncbi.nlm.nih.gov/pubmed/21131864
4) http://www.ncbi.nlm.nih.gov/pubmed/24628553
I read the entire article, and, while your research looks thorough and you conclusion is appropriate, I’m having trouble believing injecting insulin doesn’t promote muscle growth. The anecdotal reports of many big men on insulin plus protein are all over the Internet and bodybuilding. Are you saying they are wrong or experiencing placebo effect?
Hi Arlow,
There are TONS of anecdotal reports big men are doing that seem wrong. However, in this particular instance, they may be right. Not that our review concludes that supraphysiological amounts of insulin do stimulate muscle growth (i.e. in amounts MUCH higher than the body can normally produce, and what bodybuilders inject).
Very interesting article and I enjoyed reading it very much! Keep them coming! My comment is this: Carbs after workout help preserve proteins from being used as energy thus saving them for protein synthesis. Carbs are thus muscle sparing. Adequate amounts of amino acids are the building blocks but if those blocks are needed first to fuel the “bricklayer” then they never get to build the “wall” so to speak. The vast majority of the amino acids used in protein synthesis come not from the diet but from body proteins. To much protein from the diet is broken down to carbon skeletons which are then used for either energy (if not supplied glucose from Carbs) or fatty acids (stored). Since the body prefers to use Carb sources for energy having adequate carbs protect the amino acid pool and supports protein synthesis as needed. One possible reason measuring insulin effects only does not reveal much is because the body uses Glucagon hormone when glucose levels are low, a post workout condition. Glucagon stimulates gluconeogenesis to gain glucose from protein. So, in short, I still promote adequate amounts of carbohydrates post workout to preserve muscle building proteins and restore glycogen to the muscles and liver.