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The Truth about Building Muscle on a Ketogenic Diet

by | Apr 26, 2025 | Body Composition, CrossFit, Exercise Performance, Health and Fitness, Health Science, Ketogenic Diet | 0 comments

The Debate Rages on

If you’re following a ketogenic diet or thinking about starting, you may be wondering about the impact it will have on your athletic performance and ability to gain muscle. If you’re anything like me, you’ve been overwhelmed with experts telling you that you need carbs, keto will kill your gains, and being fat-adapted isn’t sustainable. On the flip side there are also experts who have tried a ketogenic lifestyle and/or studied it in a clinical setting who are saying that it’s just as effective, with some possible additional benefits, as traditional nutrition recommendations.

Some of the most animated and passionate arguments I hear are from people fighting to maintain that carbs are essential for building muscle. I don’t understand the vehement conviction this topic elicits from people. I think anyone truly interested in optimizing performance would be curious about new ways to achieve that goal.

This is one of those classic situations where neither side is strictly right or wrong, but the language used and the context applied make all the difference in the world. Hopefully this article will help you understand what’s really going on.

In this article, I’m going to review a little background of what the current thought around carbs for building muscle is. I’ll explain where some of the logic misses the mark in light of newer data. Then, I’ll explain what happens and how a ketogenic diet supports gains just as well, if not better, than eating a pound of rice every day.

What most people hear and understand

The common thought that carbs are a requirement to build muscle comes from studies that make recommendations like this,

Then you have the thousands of social media famous PhDs, strength and conditioning coaches, body builders, and other experts who steadfastly defend and promote carbohydrates as the best option to fuel muscle growth.

“Benefits of the High-Carb, Low-Fat Diet: https://rpstrength.com/blogs/articles/case-high-carb-massing

  • Increased Insulin. Insulin is a major player in anabolism, the building of muscle. Simply put: carbohydrates secrete insulin, and insulin makes you more jacked.
  • Excess carbohydrates are less likely to be stored in the body and more likely to be used as energy. High-carb dieting provides more training energy. By eating more carbohydrates than you need for training minimums, you nearly guarantee that fuel source will not be a limiting factor for hard training in the gym.
  • Higher carbohydrate consumption might allow for quicker rebound hunger for consistent eating. The entire timeline of digesting a high-protein and super high-carb meal shrinks to lower than that of a mixed meal with fats, even when calorie-equated. This allows you to eat more often, which allows you to eat more carbohydrates and grow even more!
  • Increased anabolism via glycogen. Stored glycogen directly promotes muscle gain. The more carbohydrates you eat daily, the higher your average glycogen stores will be, and the higher your muscle-growth rates will be.
  • Carbohydrates are powerful anti-catabolic regulators and are the preferred fuel source for most energy-consuming bodily processes. The more carbohydrates you take in, especially around your workouts (which tend to risk catabolism more than other conditions in your day), the more likely you are to prevent muscle loss and let muscle accumulate to higher amounts over time.
  • Carbohydrates reduce cortisol production. Cortisol is a stress hormone catabolic to muscle tissue, promotes fatigue, interferes with sleep, and negatively impacts most recovery and adaptive processes. High-carb eating means lower cortisol levels and all-around better recovery and adaptations to training.”

The dependence on calories over nutrition aside, there are many inaccuracies in statements like these that we only know about, now, because the science is new. I don’t fault many of the proponents of carbs for their knowledge or views based on what they’ve been taught and experienced.

The catch is that using carbs as a fuel source works. It’s been a mainstay in bodybuilding and sports performance for decades. The idea that fat can provide the energy needed and support building muscle does not equal carbs being bad or that they aren’t a viable option. They absolutely are. However, there are many reasons someone may want to follow a ketogenic diet and there is no evidence that a keto-adapted person will have any problems in sport performance or building muscle. These ideas are not mutually exclusive.

What I’ve seen over the last 7 years.

This isn’t a hypothetical argument for why I think you “should” be able to build muscle on a ketogenic diet. The purpose of this article is to provide a logical, mechanistic explanation for why the narrative of a carb requirement to build muscle is inaccurate and how a ketogenic diet supports the same potential for growth.

My personal experience of following a carnivore diet since May of 2018 has been nothing but amazing. Everything I’m going to explain in this article is something I have experienced as an over 50 CrossFitter who has only seen improvements in all aspects of fitness performance since making the change.

I have helped numerous runners, cyclists, swimmers, CrossFitters, bodybuilders, powerlifters, etc…, transition to a ketogenic diet. Every single one has seen improvement in their training volume, recovery, overall health, and performance. The process of transition for athletes is repeatable and consistently successful when it’s done properly.

I have many colleagues who perform at high levels in their sport who follow a ketogenic diet. Here are a few that you can see are doing quite well.

  • Natalie Grasso @theketobikinipro (Bodybuilding)
  • Robert Sikes @ketosavage (Bodybuilding)
  • Robbie Moyles @robbie.moyles (CrossFit)
  • Zack Bitter @zackbitter (Ultra-marathons)
  • Shawn Baker @shawnbaker1967 (Rowing and Power Sports)

There is a lot of perspective to be gained when you can look at the data and evaluate its consistency against what you’ve seen with your own eyes. There is not a single finding or conclusion of a study that can contradict what we see in the empirical evidence around us.

OK, I’m straying a bit from focusing on muscle building, so let’s get into the main points of what we need to build muscle and where inaccuracies in the current narrative come from.

What we need to build muscle

Beside the need for energy to enable training, there are only four specific inputs required to build muscle mass. This shouldn’t be a surprise to anyone who has listened to, or read, any of my content the last few years. The fundamental components to building muscle are protein to build, adequate stimulus (training with progressive overload) to signal the need to build, sufficient recovery to allow time to build (supercompensation), and we need enough sleep to optimize anabolic hormone activity.

That’s it. Protein, training, recovery, and sleep are the building blocks of muscle gains.

Notice I didn’t mention fuel or calorie surplus. We’ll talk about the fuel piece in this article. You’ll have to wait for the calorie deep dive. That one will be a great read.

Confusion, apples, and the infancy of ketogenic research

Before I go any further, I want to clarify three things that must be considered in this discussion.

A major paradigm shift

First, the processes involved with glucose availability, storage, utilization, and replenishment is not dependent on exogenous sources of carbohydrates. Does the body need glucose? Absolutely. However, that does not equal a requirement to eat carbs (more on that later).

Many of the protocols around carbohydrates as the primary fuel for building muscle are based on muscle glycogen depletion during exercise. The problem with this basic concept is that muscle glycogen depletion in resistance training doesn’t happen to the point where it impacts performance. Current data for carb-fueled athletes is that performance doesn’t take a hit until around 50% or more depletion. Here are two studies to consider.

Concerns about glycogen depletion are predominantly discussed in the context of endurance activities that last more than 1–2 hours https://link.springer.com/article/10.1007/s40279-013-0079-0

In fact, we’re finding that hypoglycemia (low blood sugar) plays a more impactful role in fatigue than muscle glycogen stores. https://pubmed.ncbi.nlm.nih.gov/39786965/

Opinion: I think lactate threshold and electrolyte balance play a bigger role than we give credit for in mechanical efficiency and energy availability during resistance training. These all need to be considered in the equation for improving performance.

As the basis for why we “need” to eat carbs for building muscle, the idea that there is a performance decrease due to a lack of available muscle glycogen during resistance training is inaccurate, especially in the context of a ketogenic diet.

  • “Muscle glycogen is an important substrate for resistance training because repeated contractions of near-maximal loads stimulate glycogenolysis, resulting in a reduction in glycogen stores of 25%–40%. However, based upon the available literature, it appears as though low muscle glycogen levels do not impede muscle protein synthesis or the overall anabolic response to resistance training”. https://pmc.ncbi.nlm.nih.gov/articles/PMC6019055

Apples to Oranges

Secondly, research on non-keto-adapted athletes is not viable as a 1:1 correlation for keto-adapted metabolic function. There are several differences in the expected outcomes of a carb-loaded athlete that just don’t have the same results in a keto-adapted athlete. Here are a few examples:

  • Ketones inhibit glycolysis and reduce the amount of glucose used for fuel
  • Shifting to a ketogenic diet reduces lactate production and increases lactate threshold performance
  • It’s well documented that keto-adapted athletes use fat for fuel at much higher intensities and for longer than carb-fueled athletes.

Most traditional research does not take these things into account. The recommendations being made are based on and should be categorized as “For Carb-Fueled Athletes” instead of an assumption that everyone should follow them.

Ketogenic science is just getting started

Lastly, up until the last 20 years, few studies have been conducted on the metabolic effects of ketogenic adaptation in sports performance.

These three findings upset the status quo by challenging the accepted notion that glucose is the predominant fuel at high intensities and that the body’s ability to store glycogen is the primary determinant of performance.

You can’t build muscle without eating carbs.

Earlier in this article I included an excerpt from Renaissance Periodization as an example of the most common items used in the argument for carbs as a requirement to gain muscle.

Lately I’ve been hearing a new, less hardline narrative from several well-known fitness influencers. The new language around this topic is a softer stance on the “need” or “required” wording. There has been a shift to acknowledging that while it is possible to gain muscle without eating carbs, it’s easier and faster to do it with carbs. This is no more valid an argument than the initial one.

This scope review makes reference to just about every point on the pro-carbs punch list. https://pmc.ncbi.nlm.nih.gov/articles/PMC6019055

Here is what much of the existing literature says and what you’ll hear from many of the experts out there.

  • Carbs are the body’s preferred fuel source for high-intensity exercise, which is crucial for muscle building.
  • When we consume carbs, they are converted to glycogen and stored in our muscles, ready to be used for energy during workouts.
  • By providing sufficient carbs, we prevent our body from breaking down muscle tissue for energy, allowing protein to be used more effectively for muscle repair and growth.
  • Eating carbs after exercise helps replenish glycogen stores, facilitating faster muscle recovery.
  • Insulin promotes glycogen storage and amino acid uptake by the muscle

Ketogenic Muscle Building

Alright, we’ve finally arrived at the big reveal. Let’s walk through some of the specific mechanisms and functions of the body that explain how we get energy for resistance training without eating carbs and how that impacts our capacity to build muscle.

“Preferred Fuel”

Any claim that a substrate is “preferred” over another is usually misapplied logic. The human body is designed to adapt and make the best of whatever situation it is in. If you overload it with carbs, it will prioritize carbs as a fuel source. If you load up on alcohol, it will prioritize alcohol as a fuel source.

Oxidative priority plays a role in how the body determines what nutrients it will process first. The biggest factor in that selection is how much storage does the body have for it, and how much of it is floating around in the body already. Here’s a graph that breaks down the order and provides a quick explanation.

The definition of preferred fuel is dependent on the internal environment that is created in the body.

The question is not what fuel the body prefers. The thing we should be looking for is what fuel provides the most consistent and available energy at the lowest metabolic cost. The answer to that question is unequivocally, fatty acids.

Not only does fat provide fuel for longer and at higher intensities of work than we ever thought, but it also provides the ideal pathway for replenishing glucose and stored muscle glycogen.

Glycogen storage

I’ve already demonstrated that in the realm of resistance training, concerns about carb depletion are unfounded. Another aspect of muscle glycogen storage is the idea that we need carbs to replenish them as fast as possible and there is an inability to do that without exogenous carbs.

Remember, earlier, when I said that we absolutely need glucose for energy but that doesn’t mean we have to eat carbs to get it?

Enter, Gluconeogenesis (GNG).

Little known fact, ketogenic adaptation supports GNG by providing a readily available substrate in an environment where it has no competition for utilization. When carbs are restricted, a few really cool things happen.

  • Because Fatty acids provide an increased source of energy during resistance training there is less of a need to break down muscle glycogen
  • Ketones attenuate glycolysis so even available glucose is used less overall
  • Ketones potentiate lipolysis which increases the breakdown of body fat for energy.
  • Increased lipolysis makes more glycerol available to GNG to replenish glycogen stores.

What we end up with is a situation where not only is glycogen breakdown inhibited, but a highly efficient substrate to replenish it is now freely available. We see the effect of this in a number of studies that show comparable, post-exercise, muscle glycogen levels in both carb and fat fuel athletes. (Notice the references to length of adaptation.)

  • “Glycogen resynthesis after such depletion may be complete within 24 h even on low carbohydrate intakes via carbohydrate-independent pathways, especially in trainees habituated to the training in low-carbohydrate conditions.” https://www.mdpi.com/2072-6643/14/4/856
  • “Compared to highly trained ultra-endurance athletes consuming an HC diet, long-term keto-adaptation results in extraordinarily high rates of fat oxidation, whereas muscle glycogen utilization and repletion patterns during and after a 3 hour run are similar.” https://www.sciencedirect.com/science/article/pii/S0026049515003340?via%3Dihub

Think about it this way. Excess glucose is stored by being converted and moved into body fat. What is the purpose of this, if there wasn’t a way to reverse the steps and access the glucose when it’s needed? Is it possible that our biology has the processes in place to support its own needs and we don’t have to force feed carbs in order to be optimal?

Muscle preservation

The argument for carbs being anti-catabolic stem from the idea that they are “protein sparing” and prevent the breakdown of muscle by providing an alternate fuel. There is one major flaw in that logic.

Any substrate other than protein, will spare protein. It’s not a benefit of carbs. It’s simply the presence of something else the body can use. Ketones actively increase the availability of fatty acids for fuel which is also protein sparing.

Even more amazing is that ketones interact with other processes to attenuate proteolysis and directly prevent the breakdown of protein in the body. On top of all that, ketones also influence and promote muscle protein synthesis.

Different from glucose being protein sparing as a consequence of simply being an alternative fuel, ketones actively reduce the breakdown of proteins for energy and support the building of muscle..

Post-workout recovery

A topic often used to support carbs, is to help replenish glycogen stores during recovery periods. Since I already covered this, let’s discuss something few proponents of carbs discuss, the impact of oxidative stress and its effect on recovery.

In conditions of excessive stress or inefficient function of processes in the body, we get an increase in free radicals and oxidants that can wreak havoc on every aspect of metabolic function. This is referred to as oxidative stress and sometimes, inflammation. https://www.sciencedirect.com/science/article/pii/S2095254620300399

Oxidative stress is a result of exercise because exercise is a stressor. We see this as delayed onset muscle soreness (DOMS), increased fatigue, and longer recovery times. The challenge is getting enough exercise to receive the benefit without creating a situation where the oxidative stress is more than the body can manage. The recovery process is defined by how well the body can clear and reduce the oxidative stress created by the workout.

This is where nutrition makes a big difference.

Carbs at worst, increase oxidative stress and at best, don’t reduce it. Ketones produce fewer free radicals, act as antioxidants, and promote the production of antioxidants.

By creating less stress during exercise and helping the body clear and manage stress post-exercise, a ketogenic diet supports higher volumes of training and faster recovery times. This increases the Maximum Recovery Volume (MRV) of athletes and can dramatically improve long-term sustainability and improvements in performance.

Note: Much of the research done in this area has only been performed on animals. My stance on this topic is based on information about biological mechanisms in the context of my clinical experience and results of reduced incidents of injury, faster recovery, and increased training volume in athletes who become keto-adapted.

Insulin

Insulin is considered to be an important anabolic hormone. This is why bodybuilders inject insulin regularly. The prevailing thought is that insulin increases glycogen storage and amino acid uptake into muscle. This is also why many experts recommend eating carbs due to the insulin response they produce.

Here’s a couple of things to consider.

Insulin and body fat

Insulin not only increases glycogen storage but also the conversion of excess glucose to body fat. This is a big reason why bodybuilders get fat when they go on bulking cycles to try and build more muscle. The problem with this is the process essentially has to be reversed when they go into a cutting phase to lose the body fat. Most of the muscle gains they may have made, are lost in this process.

This is not something a keto-adapted athlete has to consider. A ketogenic metabolism increases the breakdown of body fat for fuel, while supporting muscle building and preservation pathways in the body. It’s a win-win.

Insulin isn’t as anabolic as you think

The idea that insulin is a powerful anabolic hormone is all bro science. I know, this surprised me too! I had to rewrite drafts of this section a few times as I researched for this topic.

The overall consensus of the literature is that insulin is effective as an anabolic hormone in its ability to preserve protein and prevent muscle breakdown. Insulin is only seen to play a role in muscle protein synthesis when overall amino acid concentrations in the blood are very high. Even then, the research isn’t sure if it’s the insulin or just the high amino acids that help the process.

Basically, when it comes to building muscle, insulin does the same thing as ketones. Both of them show benefits by reducing proteolysis and preserving muscle tissue.

  • “Several studies investigating whether exogenous insulin administration can further amplify muscle protein synthesis during hyperaminoacidemic conditions consistently failed to discern an incremental effect. These outcomes suggest that while concurrent hyperinsulinemia and hyperaminoacidemia may elevate muscle protein synthesis, particularly in healthy young subjects, this effect seems predominantly attributed to hyperaminoacidemia.” https://sportsmedicine-open.springeropen.com/articles/10.1186/s40798-024-00697-6
  • “it is demonstrated that, in healthy humans in the postabsorptive state, insulin does not stimulate muscle protein synthesis and confirmed that insulin achieves muscle protein anabolism by inhibition of muscle protein breakdown” https://journals.physiology.org/doi/full/10.1152/ajpendo.00003.2006
  • “insulin does not stimulate muscle protein synthesis in the presence of increased circulating levels of plasma BCAA alone. Insulin’s suppressive effect on proteolysis is observed independently of the levels of circulating plasma BCAA.” https://pmc.ncbi.nlm.nih.gov/articles/PMC5241558/
  • “Insulin appears to have a permissive role in MPS in the presence of elevated AAs, and plays a clear role in reducing MPB independent of AA availability.” https://link.springer.com/article/10.1007/s00125-015-3751-0
  • “Changes in muscle protein synthesis were strongly associated with changes in muscle blood flow and phenylalanine delivery and availability. In conclusion, physiological hyperinsulinemia promotes muscle protein synthesis as long as it concomitantly increases muscle blood flow, amino acid delivery and availability.” https://pmc.ncbi.nlm.nih.gov/articles/PMC2804964/
  • “Insulin potentiates protein synthesis rates under conditions of hyperaminoacidemia and inhibits protein breakdown in skeletal muscle.” https://www.sciencedirect.com/science/article/pii/S1550413121001273

A way to optimize insulin?

We don’t need to worry about insulin to optimize building muscle. What if we could get some of its muscle sparing benefits without the concern of developing insulin resistance or adding a bunch of body fat?

Using carbs to stimulate insulin reduces the impact it has on protein because it has to simultaneously store glycogen and preserve amino acids.. If only there was a way to stimulate insulin without having to worry about excess glycogen. Oh wait, there is!!

Did you know that protein stimulates insulin too?!

Protein has been shown to stimulate insulin, in some cases more than carbohydrates. In many instances it also maintains a longer steady state of elevation than the spikes that carbohydrates cause. It’s possible that following a whole foods, animal-based ketogenic diet could layer the muscle sparing benefits of insulin on top of what we get from ketones.

But, Cortisol?

Everyone knows that cortisol is the stress hormone and if you let it get out of control it will mess up all the work you’ve put into building those bulging biceps! Cortisol is catabolic and promotes the breakdown of muscle. That’s kind of the opposite of what we’re trying to do here.

A common argument I hear is how important carbs are to managing cortisol. I hear it in the sports world and more recently in the health realm as a solution to help women in menopause. The message is that we “need” carbs to manage cortisol and support endocrine function.

Do carbs help in these area? Yes, they can, but how and are they the only thing on our list of options?

I want to emphasize that I looked at over a dozen studies on this topic. I did not find a single one that tested a specific mechanism of action. One of them even said, “The mechanism by which they occur remains elusive.” https://pubmed.ncbi.nlm.nih.gov/1549000/.

All of them only evaluated the ingestion of carbs to the level of cortisol. Since no one really knows how carbs make a difference here, let’s go over the main idea floating around as to how carbs apparently reduce cortisol.

Insulin is an antagonist to cortisol. When insulin goes up, cortisol goes down. It’s a pretty straightforward concept and it makes the most sense. Fortunately, carbs are not the only way to influence insulin. Again, we are faced with the idea that carbs may not be obligatory for cortisol management.

NOTE: The insulin discussion also includes the idea that insulin has an impact on serotonin, which can help with regulation of the Hypothalamic-Pituitary-Adrenal (HPA) Axis. https://pmc.ncbi.nlm.nih.gov/articles/PMC4314547/

Eating carbs is not a requirement for managing cortisol or anything else we’ve discussed. Cortisols impact on building muscle is not problem for a keto-adapted athlete any more than it is for a carb-fueled athlete. Overtraining and poor stress management need to be emphasised at all times, regardless of the dietary protocols in place.

Additional Considerations

I want to wrap up this discussion with a few things I think are important to the conversation about energy and fatigue during workouts, the adaptation process, and a major change in energy utilization on a ketogenic diet.

Adaptation takes time

First things first. Any study that evaluates a ketogenic diet in the context of exercise science or sports performance has a low chance of validity if it’s less than 4–8 weeks. I ‘d liked to see more studies last 8–12 weeks. I will write about this in the future, but there is a lot more to adaptation than ketosis. Unfortunately that is the standard that many researchers are using and it is producing an unfortunate amount of bad data and faulty conclusions.

There are benefits from ketosis and the increased quantity of ketones in the blood do have a positive impact on function and performance. That is only a minor aspect of the bigger picture.

Improvements can be made in metabolic function in shorter times, but most of the negative data and results from modern research of the ketogenic diet can be directly tied to incomplete or poorly executed adaptation protocols.

Lactate Threshold

Lactate production decreases and turnover increases on a ketogenic diet. This should be an obvious benefit to anyone looking to improve their performance in physical activities.

Brain Energy

20% of the body’s energy expenditure happens in the brain. Ketone utilization in the brain is another way that a ketogenic diet supports glucose sparing. Ketones are actually preferred by the brain over glucose. The brain will use ketones immediately the more they are available, even with no reduction in glucose. https://pmc.ncbi.nlm.nih.gov/articles/PMC7699472/

Not only are ketones great fuel for the brain, but they also improve cognitive performance across the board. This needs further study to see its impact on sports performance, but there seems to be some obvious benefits. https://alz-journals.onlinelibrary.wiley.com/doi/full/10.1002/alz.059627

Discussion

When compared to a carbohydrate rich diet, isolating the factors of muscle building capacity only, a ketogenic diet demonstrates no significant difference in capacity or effectiveness of increasing muscle mass.

In my clinical experience, I have not seen any indication that the capacity for building muscle is decreased on an adapted ketogenic diet. In actuality I have seen the ergogenic and recovery improvements from the reduction of inflammation, the potentiation of lipolysis, and increased metabolic efficiency. These holistic improvements to many aspects of training have a synergistic effect on improving overall performance.

Regardless of the nutrition protocol being used, training and performance protocols should be focused on sustainable, effective doses of stimulus and recovery compared against performance results. Ideally, the nutrition protocol is managed as part of the overall training solution. This includes, evaluation of performance impacts beyond energy availability or body composition.

The challenge for many, is being aware of information that goes against current knowledge and engaging in open-minded review and experimentation to see what the results may be. This is not something I see happen in the exercise and sports performance space. Especially on this topic. Few, if anyone, who argues against a ketogenic diet for sports performance has actually used a ketogenic diet in a clinical or applied manner themselves.

Collection of evidence

Here are a handful of studies and reviews that clearly demonstrate the ineffectiveness of exogenous carbs to improve muscle gains and the clear ability to maintain the same or better gains on a ketogenic diet.

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