A Ketogenic Diet and Crossfit

Is a Ketogenic or High Fat Low Carb Diet Suitable for Crossfit Athletes?

Summary: A Ketogenic or High Fat Low Carb Diet is a sustainable option for recreational Crossfitters and can help to aid in improved body composition, namely lower body fat mass, as well as potentially providing additional health benefits. However, competitive Crossfitters require higher levels of glycogen for performance than can be provided on a Ketogenic or High Fat Low Carb Diet and therefore it is unlikely that the Ketogenic or High Fat Low Carb Diet would be suitable for a competitive Crossfitter.


There is a wealth of information and evidence for positive health benefits of a Ketogenic Diet or High Fat Low Carb (HFLC) diet. There’s strong evidence that a HFLC diet helps to facilitate weight loss and may have a positive influence on the treatments of diabetes, cancer and other metabolic diseases(1–3). However, I was interested to find out if it is suitable for both a recreational Crossfitter and competitive Crossfit Athletes.

Crossfit’s founder Greg Glassman’s defines “World Class Fitness in 100 Words”: “… Practice and train major lifts: deadlift, clean, squat presses, clean and jerk and snatch. Similarly, master the basics of gymnastics: pull-ups, dips, rope climb, push-ups, sit-ups, presses to handstand, pirouettes, flips, splits, and holds. Bike, run, swim, row, etc, hard and fast. Five or six days per week mix these elements in as many combinations and patterns as creativity will allow. Routine is the enemy. Keep workouts short and intense. Regularly learn and play new sports.”(4) If we break this down, essentially Crossfit athletes need to be able to perform Olympic weighlifting, gymnastics and cardio exercise at high intensity.

I was unable to source any Ketogenic/HFLC studies on competitive Crossfit athletes however there has been some investigation into recreational Crossfit athletes and the HFLC diet.

In her masters thesis(5) Rachel Gregory studied a group of people that had been doing Crossfit for a minimum of one month before the study began. She randomly assigned them to two groups. The first was a control group who continued their Crossfit training and diet as they always had. The second group were prescribed a HFLC diet and continued their Crossfit training. Both groups did Crossfit performance tests at the beginning of the experiment and at the end which involved a 500m row, 40 air squats, 30 sit-ups, 20 hand release pushups and 10 pullups. This measure is questionable in a Crossfit context as most of the movements are bodyweight movements and there is no weightlifting in the test so it is potentially not a true measure of a Crossfit workout.

At the end of the study, Gregory concluded that “A low-carbohydrate ketogenic diet combined with six weeks of CrossFit training improves body composition and performance.”(5) However this is not truly an accurate conclusion. Based on her research both groups improved their Crossfit performance, and the HFLC group had improvements to their body composition. We could therefore conclude that doing Crossfit improves Crossfit performance and the ketogenic diet did not impede Crossfit improvements, and the HFLC diet improved body composition.

A separate study looked at twelve recreational Crossfitters over a 12 week period where five were part of a control group and seven were prescribed a ketogenic diet. The study concluded that the participants on the ketogenic diet had improvements in body composition, namely body fat mass, and did not see a reduction or improvement in performance. However, they did find that a ketogenic diet may have reduced leg muscle mass in the participants(6). This echoes the result of the study by Gregory but with the addition of a potential reduction of leg muscle mass – which, in theory, could translate to reduced performance. This would be particularly relevant when it comes to any squatting, which many Crossfit movements involve.

Explosive strength and anaerobic fitness is one of the fundamental elements of Crossfit for gymnastics, sprinting, weightlifting and so on. There have been several studies on the effects of a HFLC diet on anaerobic fitness and the general consensus appears to be that anaerobic activity requires a significant level of glycogen in the muscles. A level that, for competitive Crossfit athletes, cannot be sustained on a HFLC diet(1–3,7,8).

In an endeavour to investigate the effects of a HFLC diet on explosive strength performance, a study was done on 8 elite artistic gymnasts who were prescribed a HFLC diet for three months. The results found that there were no significant changes in performance. However, there was a significant change in body composition with a reduction in body weight and body fat mass and no significant change in muscle mass(7). Therefore we could again conclude that while a HFLC diet has a positive effect on body compositon of gymnasts, it does not have a positive or negative effect on performance.

Stephen Phinney is a Professor of Medicine Emeritus at the University of California-Davis and is known to be a leading expert on HFLC diets and metabolic syndrome. In a review of ketogenic diets and physical performance, Phinney concluded that “anaerobic (ie, weight lifting or sprint) performance is limited by the low muscle glycogen levels induced by a ketogenic diet, and this would strongly discourage its use under most conditions of competitive athletics”(1) In other words competitive athletes that perform anaerobic activity require a level of carbohydrates that is not provided for in a HFLC diet. However, Phinney did find that adaptation to a HFLC diet could be beneficial for endurance athletes.

In her review article titled, Re-Examining High-Fat Diets for Sports Performance: Did We Call the ‘Nail in the Coffin’ Too Soon? Louise M. Burke summarised that “the current interest in low carbohydrate high fat (HFLC) diets for sports performance is based on enthusiastic claims and testimonials rather than a strong evidence base. Although adaptation to a HFLC (whether ketogenic or not) increases the muscle’s capacity to utilize fat as an exercise substrate, there is no proof that this leads to a clear performance advantage. In fact, there is a risk of impairing the capacity for high intensity exercise.”(9)


It appears that for the recreational Crossfitter, performance is not sacrificed by adopting a HFLC diet and it appears that it can assist Crossfit athletes to lower body weight and assist in endurance. For elite Crossfit athletes however, carbohydrates are needed as a source of fuel for the continued heavy load and high-intensity nature of both Crossfit training and competitions.

There are a number of benefits to a HFLC diet particularly for overweight, obese, pre-diabetic individuals or those with type 2 diabetes(1–3). For the recreational Crossfitter, depending on their goals, there is evidence for an improvement in body composition (namely a reduction in body fat)(5)(6). In theory, a reduction in body weight should help to improve body weight movements because there is less weight to move, however, I could not find any definitive proof of performance improvement for Crossfitters on a HFLC diet. For the individuals in Rachel Gregory’s study, doing Crossfit made all the participants better at Crossfit.

At the end of the day, the type of diet an individual follows should be dependent on their goals. There is evidence for health benefits and weight loss while not compromising performance for recreational Crossfitters on a HFLC diet. Therefore, a HFLC diet is a viable option for people training once a day for health and fitness and looking to lower their body fat percentage.

For competitive Crossfitters, a HFLC diet is not likely to be the right approach to their performance nutrition. People training for competition and performance need a higher level of carbohydrates than that afforded by a HFLC diet. The exact amount is dependant on a number of factors including their workload.


There are always outliers in any population and there potentially could be individual competitive Crossfitters that thrive on a HFLC diet. But, for competitive Crossfitters looking for an edge and improvement, a nutrition plan that is likely to move the needle closer towards their performance goals will need to include carbohydrates. It would be advisable that they work with a nutrition coach who can understand their goals and needs, who understands the sport of Crossfit and can find a dietary plan that is right for that specific individual.


  1. Phinney SD. Ketogenic diets and physical performance. Nutr Metab (Lond) [Internet]. 2004 Aug 17 [cited 2018 May 26];1(1):2. Available from: http://www.ncbi.nlm.nih.gov/pubmed/15507148
  2. Zinn C, Wood M, Williden M, Chatterton S, Maunder E. Ketogenic diet benefits body composition and well-being but not performance in a pilot case study of New Zealand endurance athletes. J Int Soc Sports Nutr [Internet]. 2017 Dec 12 [cited 2018 May 24];14(1):22. Available from: http://jissn.biomedcentral.com/articles/10.1186/s12970-017-0180-0
  3. Chang C-K, Borer K, Lin P-J. Low-Carbohydrate-High-Fat Diet: Can it Help Exercise Performance? J Hum Kinet [Internet]. 2017 Feb [cited 2018 May 24];56:81–92. Available from: http://www.ncbi.nlm.nih.gov/pubmed/28469746
  4. Glassman G. Article – CrossFit: Forging Elite Fitness [Internet]. [cited 2018 May 26]. Available from: https://journal.crossfit.com/article/what-is-fitness
  5. Gregory R. A low-carbohydrate ketogenic diet combined with six weeks of crossfit training improves body composition and performance [Internet]. Masters Theses. 2016 [cited 2018 May 24]. Available from: http://commons.lib.jmu.edu/master201019/109
  6. Kephart W, Pledge C, Roberson P, Mumford P, Romero M, Mobley C, et al. The Three-Month Effects of a Ketogenic Diet on Body Composition, Blood Parameters, and Performance Metrics in CrossFit Trainees: A Pilot Study. Sports [Internet]. 2018 Jan 9 [cited 2018 May 24];6(1):1. Available from: http://www.mdpi.com/2075-4663/6/1/1
  7. Paoli A, Grimaldi K, D’Agostino D, Cenci L, Moro T, Bianco A, et al. Ketogenic diet does not affect strength performance in elite artistic gymnasts. J Int Soc Sports Nutr [Internet]. 2012 Jul 26 [cited 2018 May 24];9(1):34. Available from: http://jissn.biomedcentral.com/articles/10.1186/1550-2783-9-34
  8. Wroble KA, Trott MN, Schweitzer GG, Rahman RS, Kelly P V, Weiss EP. Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial. J Sports Med Phys Fitness [Internet]. 2018 Apr 4 [cited 2018 May 24]; Available from: http://www.ncbi.nlm.nih.gov/pubmed/29619799
  9. Burke LM. Re-Examining High-Fat Diets for Sports Performance: Did We Call the ‘Nail in the Coffin’ Too Soon? Sport Med [Internet]. 2015 Nov 9 [cited 2018 May 24];45(S1):33–49. Available from: http://www.ncbi.nlm.nih.gov/pubmed/26553488

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