A new study from the Australian Institute of sport has put another nail in the coffin for the ketogenic diet for endurance athletes. High fat, very low carb diets have been touted as potentially increasing endurance performance for a number of reasons; we store more fat in our body than we could ever store carbohydrate, it has been proposed as ‘anti-inflammatory’, and it has even been suggested to help our muscles respond more to a given exercise stimulus. (If you're not sure what a ketogenic diet is, we've written about it before with some examples)

To put it to the test though, the renowned Australian research group enlisted elite race-walkers (Olympic and world medalists were amongst the participants) and got them to consume either a high carbohydrate, a structured carbohydrate, or a ketogenic diet. They carried this study out and published the data a few years ago. They found that when the athlete's performance in a race was worse when they had the ketogenic diet compared to the other two. When they assessed them in the lab, they found it cost them more energy to exercise at higher intensities - so their exercise economy was worse. 

After publishing the data, they decided they would rerun the experiment to try and see if they could confirm the data.

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New Angle, Same Result

In this new study, the research group again recruited world-class athletes, put them, again, on one of three diets (two high carbohydrates and one were ketogenic). They also ran two simulated races to look at performance effects and assessed the athletes in the lab. What they also did this time allowed athletes on the ketogenic diet to try and load up on carbohydrates before the races to see if they could get the best of both worlds - have better adaptation during training when they are ketogenic, and then the benefit of carbohydrates which are a more economic fuel to use during high-intensity exercise.


The results - the same as they had previously found. Worse performance, and less economic athletes when they consume a high fat, ketogenic diet - even after they had refed briefly with carbohydrates. The reason why we suspect that the carbohydrate did not recuse performance levels, is because the ketogenic diet blunts our ability to store and then burn carbohydrate in the muscle - exactly where it is needed during exercise.


What's worse for the ketogenic diet is athletes did perform worse - they did not even maintain their pre-training levels. Whereas athletes in both carbohydrate groups improved their performance.


Pre and post-diet race times during 10km time trial. All runners on the ketogenic diet performed worse while both carbohydrate groups saw improvements.

Final Nail In The Coffin?

The results are pretty damning for the ketogenic diet for endurance athletes. But doe that mean there is no place for it at all?

Probably not. For example, a recent case study showed that an international cyclist has long been able to maintain world-class performances on a low carbohydrate diet (although he did improve when he increased his carbohydrate intake in the weeks leading to competition) (2). There are also many athletes across different sports that are reportedly competing while living on a ketogenic diet. Although even in team sports such as football, performance has been seen to be linked to carbohydrate availability.

If you are working with athletes, you need to consider their carbohydrate needs based on competition.


1 -Burke, Louise M., Avish P. Sharma, Ida A. Heikura, Sara F. Forbes, Melissa Holloway, Alannah KA McKay, Julia L. Bone, Jill J. Leckey, Marijke Welvaert, and Megan L. Ross. "Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible." PloS one 15, no. 6 (2020): e0234027.

 2 - Webster CC, Swart J, Noakes TD, Smith JA. A Carbohydrate Ingestion Intervention in an Elite Athlete Who Follows a Low-Carbohydrate High-Fat Diet. Int J Sports Physiol Perform. 2018;13(7):957–960. pmid:29252062