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building Muscle on Keto: An Evidence-Based Guide
Brady Holmer
ketosis training
Keto is a weight loss diet...but it doesn’t have to be.
Even though thousands of user testimonials and dozens of research studies have solidified the effectiveness of the ketogenic diet to promote and sustain weight and fat loss, this diet has many more applications than slimming down.
One of those applications is for athletes and individuals who want to get leaner, stronger, and even pack on muscle. However, there is a common myth floating around that the ketogenic diet—which isn’t necessarily a “high protein diet”—makes it hard, if not impossible, to gain muscle.
What’s the source of this belief, and does the criticism hold water? Should bodybuilders be adopting keto?
This article will help to clear the air on the keto diet as it relates to muscle building and dispel some common misheld beliefs along the way. We want to make the case (backed by evidence) that you can maintain and even build muscle mass while adhering to a strict ketogenic diet.
But first, let’s cover some of the basics on how to muscle is built.
Muscle protein synthesis (MPS) is the process that our body uses to build new proteins; it’s essential if we want to gain muscle mass or make our muscles larger—a process known as muscle hypertrophy.
There are a few biochemical pathways that govern protein synthesis. These anabolic (growth-promoting) pathways are activated by things like nutrients from food and, perhaps most importantly, exercise. The exercise has to be specific though.
Overloading the muscle using resistance exercise is essential to increase muscle protein synthesis and ultimately, size and strength.
So, to “get big” you have to “lift big” through weight training. But how exactly does weightlifting increase the size of muscles?
Interest in the mammalian target of rapamycin (mTOR) is growing in the area of longevity. However, this cellular sensor is also involved in the process of muscle hypertrophy and protein synthesis.
mTOR is a nutrient sensor—meaning that it can sense whether the body is in a “fed” or “fasted” state.
mTOR can also sense mechanical forces. This is where its involvement in hypertrophy comes from. When we overload a muscle by lifting heavy weights, mTOR is activated.1,2 Activation of mTOR has two functions—stimulating muscle protein synthesis and preventing protein breakdown. This has a dual effect on helping to increase muscle mass.
Interestingly, the more you activate mTOR, the more you are able to increase muscle growth and strength.3,4 It’s a dose-response effect.
mTOR can also be activated by hormones in the body known as growth factors. These include insulin and insulin-like growth factor—both of which activate mTOR and lead to an increase in muscle protein synthesis.1
All proteins (in the body and in food) are made up of amino acids. That’s why they’re often referred to as the “building blocks” of proteins. Without amino acids, we couldn’t build muscle.
Especially important to the growth and maintenance of muscle mass are the branched-chain amino acids (BCAAs).
These amino acids are also known as Essential amino acids, meaning that we must consume them in our diet because they’re not produced in the body.
Ingestion of BCAAs, especially the BCAA leucine, stimulates muscle protein synthesis through mTOR and other processes.5,6,7 Studies have shown that the BCAAs in particular are the most effective at causing muscle hypertrophy and preventing muscle breakdown, even more effective than the growth-factor insulin.8,9
Amino acids are the reason for the recommendation to consume protein after a hard workout; since this will maximally stimulate muscle protein synthesis and help you recover from your effort. While overall protein balance may be more important for muscle protein synthesis, some data show that consuming 20 - 30 grams of high-quality protein after exercise will maximally stimulate protein synthesis. Make sure to include at least 2 grams of leucine—the most potent driver of protein synthesis.
Given it's advocacy of extremely low carblow intake, the keto diet has been advised against by many in the bodybuilding and sports performance world. The idea that carbohydrates are necessary to induce muscle growth probably came from the fact that insulin and IGF-1, which both rise in response to carbohydrate intake, also stimulate muscle protein synthesis.
Furthermore, many recommendations exist that tell athletes to consume protein plus carbohydrates in the post-workout window to really maximize gains and promote recovery. Again, the thought is that the carbohydrates will stimulate insulin, promoting a greater amount of muscle protein synthesis than protein alone.
However, when studies compare protein ingestion alone to a combination of protein and carbs after resistance exercise, there is no difference in muscle protein synthesis.10,11,12,13 Long story short: the carbs don’t seem to be adding anything extra.This is probably due to the fact that the amount of protein ingested is enough to raise insulin levels and activate mTOR. More insulin doesn’t necessarily mean more protein synthesis, in this case.10,11
This might silence any argument against using the keto diet to build muscle. But another argument against keto for athletes has to do with glycogen (stored glucose) in muscle.
If glycogen stores are low during exercise, this could compromise energy availability and limit performance. Not something that any athlete wants. However, this may be more of a concern for athletes involved in endurance activities where glycogen depletion becomes an issue. Athletes in sports involving heavy lifts or bodybuilding might not experience negative effects from low glycogen.
However, the data don’t support that glycogen levels are reduced on a ketogenic diet—at least after a sufficient period of adaptation occurs.
In fact, keto-adapted athletes who were compared to athletes consuming around 600 grams of carbohydrates per day actually had similar levels of stored muscle glycogen. After exercise, the keto-adapted athletes were also able to replenish their levels of stored glycogen just as well as the carbohydrate-consuming athletes—despite consuming about 75% less carbohydrates during that period.14 Something happens to keto-adapted athletes that allow them to maintain glycogen levels at a high level. But what?
Maintenance of glucose and glycogen levels in the body in the absence of carbohydrate consumption can occur through a process known as gluconeogenesis, or GNG for short. GNG is a process that our body uses to create glucose out of non-carbohydrate sources—mainly amino acids and glycerol from fatty acids.
By “manufacturing” glucose from these other substrates, low-carb athletes are able to replenish and maintain muscle glycogen at similar levels to carb-consuming athletes.
So, the fact that carbs aren’t needed to build muscle or to keep up a sufficient amount of glucose and glycogen to fuel athletic activity is a nail in the coffin against the keto diet for athletes looking to get bigger, stronger, or perform longer.
But we are primarily interested in muscle growth for this article. While the foundation is sound, what does the evidence actually say about building muscle on a ketogenic diet?
Where did the idea that you can’t build muscle on keto come from?
For one, there is the idea that low-carbohydrate diets will fail to sufficiently stimulate insulin/IGF-1 in response to training and therefore, impair your ability to grow muscle or even cause muscle loss. Some people think that if you don’t consume carbs alongside your protein, you won’t maximize muscle protein synthesis.
The second and perhaps most cited reason is that the ketogenic diet is one in which protein is moderated—keto doesn’t encourage a super high intake of protein; keeping it around 10 - 15% of total calories. The theory goes that, since protein is essential for growing large muscles, restricting your intake might lead to a significant loss of muscle tissue or an inability to get bigger.
As we will see, the data don’t really support either of these takes.
This is a generally new area of research, so we don’t have a ton of studies. However, some research has been done that points to a net benefit of the keto diet on markers of muscle growth and maintenance.
Building muscle is great, but another goal of many strength-based athletes is to optimize body composition. A low-carb high-fat diet can do this. Research has shown that athletes who adopt a keto diet experience greater body fat loss than a group of high-carb dieters.15,16 After 8 weeks of a keto-diet and resistance training program, young men experienced reductions in fat mass and visceral adipose tissue—changes that weren’t seen in the non-keto groups.17
It makes sense that fat mass would drop and body fat % go down on a keto diet once you "learn" to efficiently burn fat for energy.
Being keto adapted ultimately leads to a greater ability to utilize fat from food and body storage areas.
As long as lean mass is maintained (which most studies show is the case), increased fat burning capacity will result in improved body composition—less fat and more lean muscle.
Fail to eat enough protein, the saying goes, and you’ll shrivel up, lose muscle, and go frail.This fear is instilled by people who say that keto doesn’t contain enough protein to maintain lean muscle mass.
However, research shows exactly the opposite—that the ketogenic diet actually prevents muscle from being broken down. When an equal number of calories are consumed on diets containing the same amount of protein but differing levels of carbs, the lower-carb diets actually maintain lean muscle mass to the greatest extent.18
Ketosis might actually improve our ability to utilize proteins. This could be due to the fact that the body no longer needs to breakdown protein for gluconeogenesis—instead utilizing ketones, sparing the protein we have. Studies support this. During ketosis and infusion of ketone bodies, it is shown that the utilization of BCAAs for energy is reduced, leading to enhanced protein synthesis and muscle maintenance.19,20
Not only do ketones spare protein for muscle maintenance, but they actually can significantly increase muscle protein synthesis. Athletes who ingested a ketone supplement made of a BHB monoester had increased activity of mTOR, leading to a doubling of protein synthesis.21
Ketosis seems to have some profound effects of various markers of protein synthesis within the muscle. But how do athletes on a ketogenic diet respond to training. Do the studies show that muscle mass can improve?
