If you like building muscle, the ketogenic diet is likely not for you
This post will be brief. I want to look at a recent paper that has been making the rounds online that aimed to “evaluate the effects of a ketogenic diet on body composition, muscle mass, strength and some blood parameters […] in competitive bodybuilding athletes.” This is the first study of its kind in bodybuilders—and let’s just say there is much to be desired after reading this one.
On to the study!
Effects of two months of very low carbohydrate ketogenic diet on body composition, muscle, strength, muscle area, and blood parameters in competitive natural body builders
Antonio Paoli et al. Nutrients 2021 
Starting with the methods, the study was a randomized, parallel trial wherein subjects were assigned to follow either a ketogenic diet (<50 g carbohydrate per day ala Atkins) or what the authors call a “Western Diet” which essentially just meant higher carbohydrate intake (set at 55% of total calories). Diets were prescribed for eight weeks alongside the subjects’ habitual resistance training (more on this in a second). Total calories were effectively matched between the groups, as was protein intake, with both groups consuming a sufficient 2.5 g/kg body weight—more than enough to support muscle accretion . Thus, the only difference between the diets was the proportion of carbohydrate and fat. Calories were set (it is assumed) to maintain body weights. Call me crazy, but more discussion on how they assessed energy needs and prescribed the diets to ensure that all subjects were in energy balance would have been nice.
The subjects were between 20 and 40 years old and all were competitive natural bodybuilders in Italy. (For the uninitiated, ‘natural’ means no anabolic steroid use. This was assessed via self-reporting.) Body composition, strength, and a host of metabolic blood-related parameters were measured pre- and post-diet under controlled conditions. A limitation among the assessments was the use of solely bioelectric impedance analysis (BIA) for body composition analysis. It is well established that BIA is highly susceptible to changes in hydration status —which is of concern especially with low-carbohydrate diets that induce glycogen and water losses. I realize researchers often only have the methods that are available to them at the time of investigation. Regardless, the limitations of BIA should be acknowledged and factored into the overall impacts of the findings.
Since we are discussing limitations, perhaps the biggest limitation of the study was the complete lack of dietary control. The authors play this off by saying that body builders “slavishly follow prescribed diets” as if this is any confirmation of dietary adherence. If this truly is the case, then it should have been unquestionably easy to have them report their weekly intakes—or at least 3-day diet records. Apparently, this did not take place. Given the rather high fat intake in the ketogenic diet group (at 264 g per day!) I would have liked to see “actual” intakes reported over the eight-week period. (Perhaps they all resorted to slugging high quality Italian olive oil to meet their fat intakes?)
Another huge limitation was the lack of training reporting (which the authors did acknowledge in their discussion). Consequently, we have no idea what the training programs looked like across subjects and between the groups. While we might be able to infer similar training styles given time of study relative to their competitive season, reporting of actual training volumes, frequencies, and intensities could have easily been assessed and reported for more context. Unfortunately, we are left wanting.
Finally, the authors state that measurements of blood ketones (as taken by the subjects themselves) were used ensure dietary adherence to the ketogenic diet. No data was presented on any of the subjects and we must assume that all maintained blood beta-hydroxybutyrate (i.e. the major ketone produced during ketosis) above the cut off reported by the authors (i.e. >0.5 mmol/L).
What did the researchers find?
The main outcomes were body composition, muscle mass and maximal strength on squat and bench press. The authors also assessed a host of metabolic parameters that I find uninteresting. (The paper is freely available for those who are interested.) I will begin with the strength findings.
Both groups significantly increased their one-repetition maximum (1RM) strength on back squat and bench press following the diet period with no significant differences between the groups. I will note, if bodybuilders cared solely about adding strength, the Western Diet edged out a better outcome when it came to the squat (6.4% increase vs. 3.6% in the ketogenic diet group). Bodybuilders, however, are not powerlifters, so a couple extra pounds on squat is unimportant in itself for what physique athletes are concerned about.
On to the things that bodybuilders do care about—body composition and muscle mass. While both groups did lose some body fat, only the ketogenic group lost a statistically significant amount (see figure below). Further, the ketogenic diet did not lead to any improvements in fat-free mass—possibly due to the limitations of BIA mentioned above. Contrastingly, the Western Diet did lead to an increase in fat-free mass—i.e. what every bodybuilder wants to achieve when training.
Interpretations & impressions
Given the above, how should we interpret these findings? In light of the aims of the study and the results as is, the ketogenic diet was lackluster for gaining fat-free mass and just fine for maintaining strength compared to a diet higher in carbohydrate. If you are a bodybuilder, this is likely not the best strategy for you, given that bodybuilding actually requires the accretion of lean tissue and not the maximization of 1RM strength on squat and bench. While the greater loss of fat mass is nice, that is what ‘show prep’ is for. The idea is to maximize muscle mass before prep begins.
Let us also consider the lost fat mass some more. This was not due to some metabolic magic of the ketogenic diet [4, 5]. Without dietary reporting, we have no idea how much calories were (likely) reduced on the ketogenic diet. Indeed, research suggests a spontaneous reduction in calorie intake with a low-carbohydrate, high-fat diet [6, 7].
Ultimately, not much can be inferred from one (rather poorly controlled) study. Nevertheless, based on what little information we have, if you are a bodybuilder looking to maximize muscle gains, the ketogenic diet is not likely (key word) your first or best choice. Until better controlled data is available, I say stick with the carbs while you can—you are likely going to be limiting them during show prep anyway.
#YOLO or some such thing.
One final comment
For the perspicacious reader, you noted the statement of “muscle area” in the manuscript title. There was no such measure of muscle area to be found…
1. Paoli, A., et al., Effects of Two Months of Very Low Carbohydrate Ketogenic Diet on Body Composition, Muscle Strength, Muscle Area, and Blood Parameters in Competitive Natural Body Builders. Nutrients, 2021. 13(2): p. 374.
2. Iraki, J., et al., Nutrition Recommendations for Bodybuilders in the Off-Season: A Narrative Review. Sports (Basel), 2019. 7(7).
3. van Marken Lichtenbelt, W.D., et al., Body composition changes in bodybuilders: a method comparison. Med Sci Sports Exerc, 2004. 36(3): p. 490-7.
4. Hall, K.D., et al., Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity. Cell Metab, 2015. 22(3): p. 427-36.
5. Hall, K.D., et al., Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am J Clin Nutr, 2016. 104(2): p. 324-33.
6. Nordmann, A.J., et al., Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials. Arch Intern Med, 2006. 166(3): p. 285-93.
7. Westman, E.C., et al., Low-carbohydrate nutrition and metabolism. Am J Clin Nutr, 2007. 86(2): p. 276-84.