Can You Build Muscle on the Low Carb Ketogenic Diet?

By now I’m sure that you know that the ketogenic diet features very low amounts of carbohydrates (5-10% of calories) plenty of fat (75-85% of calories), and low to moderate protein (10-15% of calories). You probably also know that people use the keto diet for weight loss and to suppress their appetite. But what if your goal is to maintain or gain muscle mass? On the surface, keto doesn’t quite sound like the right diet for bulking up. Don’t we need a ton of protein to build muscle? What about those carbs? We need carbs to stimulate insulin for muscle growth, right? Doesn’t keto actually cause loss of muscle?

Despite these concerns, many people claim they maintain or gain muscle mass on keto. In fact, research agrees that most of the weight loss on keto is fat (after some initial water loss), not muscle (Volek2002) (Willi1998). Before we look deeper into the studies on the effects of keto on muscle mass, let’s review some basics about the biochemical mechanisms involved in muscle growth and maintenance.

What is required and not required for muscle protein synthesis

A special protein called “mTOR” is a major player in building muscle mass. It seems appropriately named given this role, as it may bring to mind the God of Thunder in Viking mythology, similarly named “Thor” and associated with power and strength. While, (disappointingly!) there’s actually no connection to Thor, mTOR (mechanistic target of rapamycin) anchors a powerful signaling pathway that switches on the cellular “machinery” the body uses to manufacture muscle protein (Yoon2017).

Resistance Training

You’ve probably heard of the old saying ‘use it or lose it!’ This is very relevant to muscle growth, with resistance training being a key trigger for muscle growth. Throughout life, our muscle mass is maintained by a tightly regulated balance between protein synthesis and protein breakdown. Inactivity can lead to protein degradation and muscle loss, while resistance training such as weightlifting (“mechanically overloading the muscle”) activates the mTOR pathway to increase muscle protein synthesis and counter muscle breakdown (Yoon2017) (Sandri2013). This can lead to an increase in muscle size (aka: hypertrophy) and strength. Exercise that is more intense leads to greater activation of mTOR and increased muscle growth (Schoenfeld2010) (Terzis2008).

Natural Hormone Release

Apart from resistance exercise, major triggers that activate mTOR include insulin and insulin-like growth factor 1 (IGF1). Both are potent anabolic (tissue building) hormones. These hormones are important for muscle growth but not essential. 

Essential Amino Acids

There’s no muscle building without amino acids! In addition to being “building blocks” for muscle protein, essential amino acids from protein foods directly stimulate mTOR and muscle protein synthesis – and to a much greater extent than insulin (Fujita2006) (Atherton2012) (Fujita2007). 

Among the essential amino acids, the branched-chain amino acids (BCAAs) – particularly leucine – are the most effective at not only triggering muscle growth, but also at suppressing muscle breakdown (Fujita2006) (Shimomura2010) (Duan2015).

During the post exercise recovery period, the general consensus is to consume 20-30 grams of protein to maximize muscle protein synthesis. This protein source should provide ~ 2 grams of leucine – a key driver of protein synthesis (Reidy2016) (Glynn2010). Animal-source protein is more effective at building and sustaining muscle mass than plant-source protein (Wu2016). Consuming enough high-quality protein with each meal may actually be more important for muscle maintenance when you’re not training. Dietary protein can provide the stimulus for mTOR activation and protein synthesis that’s missing on rest days (English2010) (Gorissen2015) (Atherton2010).

Carbohydrate?

It’s clear that protein consumption after resistance training promotes muscle growth. So, what about those carbs?

According to current dogma, ingesting carbs along with protein following workouts will enhance the anabolic effect of exercise by raising insulin levels. However, the evidence does not support this claim. Several studies have shown that the combined effects of carbohydrate and protein ingestion after resistance exercise does not further increase muscle protein synthesis versus protein intake alone (Staples2011) (Koopman2007) (Miller2003) (Glynn2013). The relatively low concentrations of insulin stimulated by dietary protein (e.g., whey protein) is sufficient to achieve maximal increase in muscle protein synthesis and/or reduce protein breakdown. The additional rise in insulin levels triggered by carbs does not appear to provide an even greater stimulus for protein synthesis (Staples2011) (Koopman2007).

Another common belief is that carbs are necessary after all workouts to replenish muscle glycogen (stored carb energy) levels. However, after a long period of adaptation to ketosis, muscle glycogen levels are the same as in athletes who eat a normal, higher carb diet! In a ground-breaking study, elite ultra-marathoners and ironman triathletes who were keto-adapted for an average of 20 months had similar rates of glycogen repletion post-exercise compared to athletes on a high carb diet. The low-carb athletes consumed only 4 grams of carb and 31 grams of fat after exercise, whereas the high-carb group ingested 43 grams of carb and only 14 grams of fat (Volek2016). So where is the glycogen coming from if there are no carbs in the diet? The synthesis of glycogen in the low-carb athletes was likely due to a process called ‘gluconeogenesis’ whereby non carbohydrate molecules such as lactate, amino acids, and glycerol (from fat burning) are used to make glucose in the liver. The “new” glucose is then transported to muscle tissue where it is stored as glycogen (Volek2016) (Evans2017). 

So, you don’t NEED carbs to trigger protein synthesis, and you don’t NEED carbs to make muscle glycogen. But do you NEED carbs to actually do resistance training, which we know is one of the most important triggers for muscle growth….? The short answer is not really. Compared to endurance training, glycogen is less important for resistance work. While muscle glycogen is reduced by more than 60% after two hours of running (Volek2016), high-intensity resistance workouts (6-9 sets per muscle group) result in only 36-39% depletion of muscle glycogen (Aragon2013).  A post workout drink with whey protein, along with exercise-induced lactate, may be sufficient to restock muscle glycogen via gluconeogenesis (without the need for carbs).

Building muscle on keto – the evidence

Keto Burns Fat

Many features of the ketogenic diet make it ideally suited for building muscle and optimizing body composition. When on keto, carbs are not required for muscle growth or glycogen replenishment. Thus, the potential for gaining body fat from excess carbs/insulin is avoided. Instead, low levels of insulin resulting from low-carb consumption enable you to access and burn body fat for energy, helping to ‘shred’ down and achieve aesthetic and weight goals. 

Keto Spares Muscle Protein Breakdown

At the same time (as increasing fat burning), ketosis spares muscle from being broken down to provide amino acids for gluconeogenesis. This is evidenced by a study comparing three diets with equal amounts of calories and protein but differing amounts of carbohydrate. The diet with the fewest carbs (30 grams/day) caused an increase in ketones and resulted in more fat loss than the other diets. Importantly, lean tissue was preserved to the greatest extent on the keto diet. Thus, the utilization of protein is improved during nutritional ketosis. This allows you to eat less protein on keto while still maintaining muscle mass. [Note: Protein should nevertheless be prioritized over ketones, especially in older adults.]

Blood levels of branched-chain amino acids (BCAAs) are significantly increased on the keto diet. In addition to their ability to promote muscle growth, BCAAs can provide direct energy to muscle cells. Ketones and BCAAs are structurally similar. During ketosis, ketones may be preferentially burned for energy, thus sparing BCAAs for muscle maintenance (Volek2012). Intravenous infusion of the ketone beta-hydroxybutyrate in volunteers resulted in decreased use of leucine for energy and enhanced protein synthesis (Nair1988).

Ketones Activate mTOR

A “protein boosting” effect has been seen with exogenous ketones. When a ketone ester was taken after exercise, beta-hydroxybutyrate markedly enhanced mTOR signaling stimulated by leucine. This increase in mTOR activity led to a doubling of protein synthesis (Vandoorne2017). Since carb was not restricted, these results suggest that exogenous ketone esters may potentially be used by athletes who need carbs for quick-burst high-intensity performance yet benefit from muscle building as well. Alternatively, adding C8 MCT oil (which churns out the most ketones) can be added to your post-workout whey protein beverage.

Balancing Protein Consumption on the Ketogenic Diet

In some people, excess protein can kick them out of ketosis (Volek2012). Conversely, others can get into ketosis without restricting protein (Tan-Shalaby2016). For muscle building, then, it’s a win-win! Even if you need to curb your protein intake to stay in ketosis, less protein is wasted and more is used to drive muscle growth. However, priority should be given to protein over ketones! You can boost your ketone levels by supplementing with C8 MCT oil, practicing time-restricted eating, and by exercising intensely.

Human Studies of The Ketogenic Diet for Body Composition and Muscle Growth

A limited number of human studies have investigated the ability of a low carbohydrate ketogenic diet to support gains or in muscle mass with resistance training. In a recent study in college aged athletes, the anabolic effects of the keto diet were compared with a traditional Western diet having identical calories and protein. Following 10 weeks of resistance training, gains in muscle mass and reductions in body fat were found to be similar for the two groups (Wilson2017). 

Surprisingly, keto-induced muscle gains without the inclusion of a structured resistance exercise program have even been reported. A 6-week carbohydrate-restricted diet resulted in a significant but unexpected increase in lean body mass (along with decreased body fat) in a group of healthy, normal-weight men. These men transitioned from a diet of 48% carb to a keto diet of 8% carb (Volek2002).

While other studies examining resistance exercise on the keto diet did not show similar muscle gains, they at least demonstrated muscle preservation. In one such study, elite gymnasts followed a keto diet for 30 days during which they performed their normal training program. This resulted in a substantial decrease in body fat and fat percentage without compromising strength and power performance. Muscle mass was basically maintained (though there was a non-significant increase) (Paoli2012). 

Similarly, in a study in non-elite crossfit athletes, the keto diet induced major losses in body fat while preserving muscle mass. Crossfit is a high-intensity training that incorporates weight lifting and other resistance exercises. All the participants in the study significantly improved total CrossFit performance time and overall power (Gregory2017).

The positive effects on body composition without performance impairment as shown in these studies can be of great benefit to weight category athletes. For example, a wrestler who needs to make weight can use a short-term keto diet to burn body fat without undermining strength and muscle mass. 

Studies designed to specifically target muscle building on the keto diet are clearly needed. An important confounding issue with studies on ketosis is the length of time allowed for keto-adaptation. This often varies from study to study, and can certainly affect outcomes.

Summary and conclusion

Many people today are successfully building muscle on the ketogenic diet. It’s hard to argue against the keto approach, unless your only concern is muscle mass and not body fat. It’s well established that low-carb keto is a powerful tool for shedding extra body fat. 

With a calorie surplus from protein and/or fat, combined with resistance exercise, muscle growth can be pulled off as well. The payoff is a more favorable body composition. 

While adequate total protein is crucial for building muscle, eating 30-50 grams of high-quality protein per meal will supply enough leucine to trigger mTOR and switch on muscle protein synthesis. This is not an excessive protein intake. Moreover, ketones themselves are anti-catabolic, i.e., they spare muscle protein from being degraded. 

No need for carbs to build muscle. On keto, the insulin effect from protein is sufficient to promote muscle protein synthesis. Protein also serves to refill depleted glycogen stores via gluconeogenesis.

Ultimately, while building muscle is certainly possible on keto, it can still be challenging… Research on the benefits of exogenous ketone esters shows promise that they could help with building muscle. In addition to being a “super fuel,” a ketone ester drink, or C8 MCT oil, can used as a post-workout recovery supplement to encourage muscle growth and repair, while slowing muscle breakdown. It is an interesting new tool keto-athletes can use to help with muscle growth without adding carbs into their diet.

We would love to hear your experiences of using the keto diet, ketone esters, or C8 MCT oil for muscle gain and body composition optimization. Comment below and let us know how it is going!

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