Will I Lose Muscle on a Ketogenic Diet?

The ability to simultaneously gain muscle and lose fat is a rather controversial topic amongst those in the fitness industry; however, this seems to be the desired goal of anyone looking to optimize body composition. One of the biggest conundrums we face is that in order to shed body fat, we tend to cut calories so much that we lose muscle mass, and in order to build muscle mass, we tend to bring along some fat gain for the ride. These changes in body composition can happen for a number of different reasons, a few of which we will touch on in this article. In any case, the evidence is clear that a properly implemented ketogenic diet exhibits a protein sparing effect, which may allow one dieting to preserve more muscle mass than if he/she hadn’t been ketogenic. This means that we can ideally shed off that pesky lower abdominal fat, all the while keeping those prized muscles we have worked so hard to build. In this article we are going to discuss some of the mechanisms of fat loss and muscle maintenance on a ketogenic diet and why a ketogenic diet may be more ideal for attaining these goals than a traditional low fat diet.


One particular piece of dietary advice that people tend to give is the “calories in, calories out,” hypothesis which indicates that it doesn’t matter what you eat or how you eat it, just as long as you eat less than you expend. This is true to a certain degree, but far too often we tend to simplify what both of those equations mean without taking into account other variables (e.g. fiber, thermogenic effect of protein, brown adipose tissue, etc.). If you put yourself in a caloric deficit, it is likely that you will experience weight loss; however, it is possible that some of this weight loss will not come strictly from body fat, and that some of it will be a result of muscle loss. Restricting calories may cause weight loss, but the actual composition of that weight loss (i.e fat, muscle, etc.) is what truly matters. I’ve seen countless people in research and in everyday life who have maintained a relatively stable weight even after working out hard and dialing in their diet. In these instances, one could be gaining muscle at a similar rate that they are losing fat mass. Therefore it is important not to take the number on your scale at face value. If it is possible to gain muscle and lose fat at similar rates, then why do so many people tend to have a difficult time dieting and maintaining muscle mass? How could a slight alteration in their macronutrient content play a role in preserving muscle mass?

How Can I Lose Fat While Still Maintaining Muscle?

A typical ketogenic diet is comprised of only 15-25% protein, yet some research indicates that even during a caloric deficit, being in a state of ketosis can preserve muscle mass. It is critical to understand that in some of the literature a low-carbohydrate diet may not actually be a true ketogenic diet. To illustrate, some studies have shown that a very low carbohydrate diet (C:4 F:61 P:35) has similar effects to a traditional low-fat diet (C:70 F:10 P:20) on weight loss. In other words, both groups demonstrated similar losses in fat AND muscle mass (10). However, Dr. Layman (5) performed a study comparing a high protein, moderate fat, and low carbohydrate diet to a high carbohydrate, moderate fat, and moderate protein in conjunction with resistance training. Fat and total calorie intake were equal between experimental groups. Average weight loss was the same between groups but the composition of the weight loss differed. Low-carbohydrate dieters lost more fat mass and less muscle compared to the high carbohydrate group. This data suggests that increasing protein intake during a caloric deficit can help mitigate some of the muscle wasting that often accompanies dieting.

But what happens during a true ketogenic diet? A meta-regression study done by Dr. Krieger showed that diets low in carbohydrates (<7%) and moderate in protein (<25%) resulted in greater weight loss and a greater maintenance in muscle mass than a diet low in fat (4). Interestingly, the ketogenic-dieting subjects in these studies didn’t even train!


Dr. Jeff Volek performed a similar study in obese males that also looked at possible effects of resistance training in combination with the diet. In this study, Dr. Volek used a true ketogenic diet consisting of high fat and low carbohydrates. He found a comparable pattern and magnitude of change in body composition to the aforementioned study (6). He later performed another study including men and women. In this study (7) the participants were instructed to not change any physical activity behaviors and to continue with their daily lifestyle habits. The two diet intervention groups consisted of a very low carbohydrate, ketogenic diet (VLCD: 9%C: 63%F: 28%P) and a low-fat diet (58%C: 22%F: 20%P). The amount of calories that were restricted for both groups was based on the individuals’ resting metabolic rate (RMR). The women in the low-carbohydrate, ketogenic group responded much more favorably to the diet, especially in terms of trunk fat loss. Meanwhile, both men and women lost significantly more fat in the VLCD group than in the low- fat diet group. As expected, RMR decreased in both groups; however, the men in the VLCD group maintained a much higher RMR relative to their body mass than those the low-fat condition did. This has important practical applications, as most people who diet tend to have decreased metabolisms that make take a long time to recover back to baseline and in some cases may never fully return to normal.

Muscle Maintenance Methods of Ketones

There are a number of possible mechanism that may contribute to this preservation of muscle, but we are going to touch on three key mechanisms.

Ketones Can Spare Muscle


We know that the main source of fuel during a ketogenic diet comes from fat and ketones. The liver produces ketone bodies in the absence of excess glucose (during fasting, starvation, or ketogenic dieting). They then flow to extra-hepatic tissues, such as the brain and skeletal muscle, to be used as fuel in place of glucose. Ketones themselves contain a protein-sparing property, preventing the breakdown of lean muscle tissue when we become keto-adapted. When muscles are saturated with substrate available for oxidation, such as fatty acids and ketone bodies, the oxidation of muscle protein-derived amino acids can be reduced. More specifically, the major ketone body beta-hydroxybutyrate (BHB), produced by keto-adapted individuals, has been shown to decrease leucine oxidation and promote protein synthesis (11).

Adrenergic Stimulation

The second mechanism that may contribute to the preservation of lean mass is adrenergic stimulation. We know that a ketogenic diet typically results in decreased blood sugar. When blood glucose lowers, our bodies transmit a potent counterregulatory stimulus to the adrenal gland to release epinephrine. Skeletal muscle protein mass is affected by adrenergic influences due to their hormonal ability to inhibit proteolysis (breakdown) of skeletal muscle (12). This increased level of adrenaline may strongly influence the muscle protein sparing effects of a ketogenic diet.


Protein Intake

The final mechanism we are going to look at is one we touched on earlier, dietary protein. On the road to becoming keto-adapted, our bodies are very sensitive to the types of macronutrients we ingest. In order to achieve a state of ketosis, one must be cognizant of the macronutrient composition of his/her diet. When carbohydrates are restricted under normal physiological conditions the body can tap into consumed protein and amino acid stores in an attempt to maintain energy production and various bodily functions. However, in keto-adapted individuals, utilizing fat and ketones for energy allows the body to depend on these alternative fuel sources instead of protein and amino acids. For this reason, what some might consider to be a low or moderate protein intake, turns into a rather sufficient protein intake.


The relation between muscle mass and ketogenic dieting continues to be a topic of great discussion. The research that we have discussed here demonstrates the potential for the ketogenic diet to allow one to lose more body fat and maintain more muscle mass during caloric restriction. There is evidence that this can occur with or without the addition of resistance training, although it appears that incorporating resistance exercise is ideal. While most of these studies were done in overweight or obese sedentary populations, more research is coming out on the possible uses of a ketogenic diet in resistance-trained athletes, powerlifters, and even CrossFit athletes. There truly is no one-size-fits-all approach to reaching your fitness goals. Tailoring your exercise and nutrition prescription to you is key. A ketogenic diet may be more practical and ideal next time you are looking to diet down, yet maintain your hard-earned muscle mass.

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