You need this many carbs to maximize muscle growth

Chapters:

00:00 Intro

00:47 Our new study

02:07 The result

03:09 My Online PT Course

03:33 Carbohydrates as a fuel source

06:23 Other mechanisms of carbs influence on muscle growth

07:27 Muscle growth

09:00 Conclusion

Transcript:

Fats, not carbohydrates, are the body’s preferred fuel source. Fats can provide the body with a lot of energy for a long period of time in a very efficient manner. However, when you engage in high intensity exercise, such as lifting weights, the body has to resort to burning carbohydrates as the fuel source. Carbohydrates become the dominant fuel source for lifting weights and other forms of high intensity exercise because carbohydrates can provide energy faster and without access to oxygen, in contrast to fats. Since carbs are the fuel source that your body relies on when you’re lifting weights, it would make sense that carbohydrates are necessary to fuel performance, and therefore a high carbohydrate diet should improve lifting performance So high carbohydrate diets improve muscle growth right. Wrong. That is not what we found.

We just published the first systematic review and meta-analysis on the effect of carbohydrate intake on muscle growth. You would think that this analysis had been done before, but actually no one had systematically reviewed all the available literature on this topic and meta-analyzed them in a proper manner to see what kind of the average effect is in the literature. We dug through over a thousand scientific studies, and included only studies that met the following criteria: We only included randomized controlled trials, which are the scientific gold standard, to see if an intervention causes a certain effect. The studies had to compare at least two different carbohydrate intakes and measure muscle growth using a somewhat reliable measure, usually using a two compartment model such as DEXA scans or directly measuring muscle growth via ultrasound.

We excluded studies that relied on unreliable methods such as skin folds or circumference measurements. The participants had to be performing strength training for a period of at least six weeks, and they had to be healthy adults. Importantly, we excluded studies that differed in protein intake between the groups, whether by design or statistical significance in their reported intakes because protein intake is a huge confounder in many of these studies. Many keto bros like to cite low carb studies that had higher protein intakes and therefore found superior results in the low carbohydrate group. After scouring through all the papers, we found 11 studies that met our inclusion criteria, and we analyzed them using a meta-analysis.

The result was surprisingly straightforward. There was no effect of carbohydrate intake on muscle growth. This effect was consistent in our sensitivity analyzes, meaning we left one study out and then saw if there was still an effect. The effect was robust to publication bias, there was no evidence of publication bias, and our results were consistent in our subgroup analysis. We specifically looked at studies in which energy intake was equated between the two groups. And we looked at studies in which muscle growth was directly measured instead of inferred from total fat free mass. The result was consistent in all of these cases, and in fact the result was consistent across every single study in the analysis. There was no significant effect of carbohydrate intake on muscle growth.

Our results are perfectly consistent with our previous systematic review on the effect of carbohydrate intake on strength development. In 16 out of 17 studies, there was no positive effect of carbohydrate intake on strength development, and the only study in which there was a positive effect – that study was confounded by higher energy intakes in the higher carbohydrate intake group, so the effect was likely caused by higher energy intake, not the higher carbohydrate intake. So if we need carbs for performance and our body relies on carbohydrates as the fuel source to produce high intensity movement, how can it be that higher carbohydrate intakes don’t improve performance and muscle growth?

The reason for this is that your body primarily relies on stored carbohydrates, namely glycogen that is stored in our muscles. When you’re training a muscle group, most of the energy that that muscle group uses comes from within that muscle group. It’s already stored there. It’s glycogen, a stored form of glucose. The reductions in glycogen stores from a typical strength training session are at most 40%. Even very high volume training in bodybuilders has often led to less than 30% reductions in total glycogen stores. Strength training simply doesn’t burn that much energy. It relies heavily on eccentric muscle actions, which are very energy efficient, and there are very long rest periods in between your sets. So the total amount of energy production, and specifically the total amount of energy production that has to be sourced from carbohydrates is simply not that high.

You can easily run some numbers and conclude that if you burn 400 calories above basal with a strength training session, even if all of that were stored from carbohydrates, you would be burning about 100g of carbohydrate. And most athletes store about 500g of glycogen in their bodies. In reality, much of the energy production during high intensity exercise comes from the creatine phosphate system, not carbohydrates, and there’s also a very significant component of aerobic metabolism, meaning fats are still used for energy relying on oxygen, because a lot of that can take place in between sets. And even during the sets, there’s still a baseline level of energy production that comes from fats, not from carbs.

So mechanistically, it makes perfect sense that if you’re not doing obscenely high training volumes, you simply don’t burn enough of the glycogen that is stored in the muscles to maintain high performance. You don’t reach critically low levels of depletion. And afterwards the body has multiple pathways by which it can re-synthesize the glycogen, even on a low carbohydrate diet, as long as it has at least 24 hours to achieve this. If you have less time than this, then you do need a high carbohydrate intake to rapidly re-synthesize glycogen stores. If the body has many hours in between strength training sessions for the same muscle group, it can easily re-synthesize most of the glycogen back using the Cori cycle, the glycerol backbone of triglycerides, meaning fats actually fuel the glycogen re-synthesis, and the body can, of course, also use whatever carbohydrate you still consume and even the protein that you consume if you consume in excess of it. The latter is obviously not desirable though.

So if you’re not training fasted and you’re not doing ten plus sets per muscle group per session, then glycogen depletion is generally not a factor. I would note that strength training differs considerably from sports like tennis, in which the level of glycogen depletion is far, far higher. Many team sports induce glycogen depletion levels in a range of 50 to 90% if the volume is high enough and performed at a high intensity without adequate carbohydrate intake. The total amount of glycolytic energy expenditure is simply far, far higher in most team sports than it is from a weightlifting session.

You might think that there are also other mechanisms by which high carbohydrate intakes could improve muscle growth outside of the effect on performance. Most of these mechanisms, though, are very ill defined and the best mechanism doesn’t make any sense. The best mechanism is that carbohydrates are needed for insulin, and insulin reduces muscle protein breakdown. This is true, but protein intake makes carbohydrates completely redundant because protein is also insulinogenic. So when you consume enough protein in your diet, as you shoot on a high protein diet as a lifter, you already produce enough insulin from the protein to make it unnecessary to also consume carbohydrates on top of that. There is no further benefit to elevating insulin levels beyond this level. You would need to start injecting very high dosage of it, probably combined with growth hormone and other stuff that pro bodybuilders do, but for a natural lifter, it’s not a consideration.

The same goes for insulin like growth factor 1 which is heavily reliant on insulin production. Some people also believe that high carb diets are good for testosterone production. The truth is exactly the opposite. Research is very, very clear that low carb diets, because they are high in fat, are better for testosterone production than high carb diets. So all the scientific findings and the theory actually perfectly align.

While on a superficial level you might think more carbs = = more performance = more muscle growth, it just doesn’t pan out that way. You just don’t need that many carbs for performance, and as a result you don’t need that many carbs for muscle growth. Muscle growth is primarily determined by mechanical tension on the muscle fibers. This is determined by how much weight you’re lifting and how much time on the tension you have. So it’s basically a function of your total training volume. If total training volume was not affected, there’s also no effect on muscle growth.

However, in practice, high carbohydrate diets may still be preferred. If we look at the literature on a granular level we see some trend with a weak effect size of high carb diets resulting in more muscle growth, specifically in the studies in which people overeat as a result of the high carb diets. Typically, when you restrict carbohydrate intake significantly, especially if you go fully keto, you basically cut out most carb sources from your diet entirely, most people have difficulty sticking to a high energy intake. This is obviously great if you’re trying to lose fat, and many of these studies in fact find unintentional fat loss. But it’s not great if you want to stick to a high energy intake and you’re trying to bulk. So in practice, low carbohydrate diets might be easier for adherence for a fat loss diet, whereas for a muscle growth diet and bulk, when you’re trying to be in energy surplus, high carbohydrate diets might make that easier.

This also explains what we see in practice, that people on low carb diets typically get lean relatively easily, but they have difficulty building muscle, whereas people that do high carb diets, they have more difficulty getting lean, but they build muscle easier. This is not because of carbohydrate intake, it is because of energy intake. Talk long; didn’t watch. So here’s the conclusion. Most natural lifters don’t need high carbohydrate intakes. In fact, they don’t need pretty much any carbs for maximum muscle growth, provided that their energy intake and their protein intake are sufficient.

Some exceptions to this are people that do bro splits, when you do at least ten sets per muscle group per session. It has to be per muscle group, not per body, because the body burns the energy from that muscle in that muscle group. So the energy, the glycogen that is stored in a certain muscle group is used specifically by that muscle group. So only the volume per muscle group is what matters. If you’re doing ten plus sets for one muscle group per session, you might actually induce critical levels of glycogen depletion, specifically in your type II muscle fibers. However, this is probably a bad idea anyway.

As I explained in my recent video, the evidence shows that very high volumes per session like this have massively diminishing returns, and you are better off splitting that volume off to a separate workout. This conclusion also assumes that you’re not training fasted. I have videos on fasted training here, in general, it seems to be a bad idea, though recent research shows that the effect is not as large as we previously believed. Which again aligns with the current findings that the carbs are just not that important for either performance or muscle growth for lifters.

Which brings us to the last caveat: This specifically refers to people doing strength training, weightlifting, Olympic weightlifting, powerlifting, bodybuilding, something like that, not team sports that are far more glycolytic and rely on far more glycogen expenditure during a workout. So these findings do not apply to most other sports, if bodybuilding or weightlifting is even a sport to begin with. Basically, our findings provide strong evidence that carbs are overrated for muscle growth. If you like this type of evidence based content I’d be honored if you like and subscribe.