Two muscular men lifting a kettle bell

Is Keto Good For Athletes? Part 2

Weight lifting kettle bells 300x200 - Is Keto Good For Athletes? Part 2


In, Is Keto Good For Athletes? Part 1, I provided an overview of ketosis, ketogenic diets and more. Here I continue with a look at ketogenic diets for athletes


Lots of athletes are now trying low/very low carbohydrate, high fat and keto diets and say they have improved performance.


This is great for them if they say so, but we need more than just testimonials and anecdotes.


There isn’t too much clinical research available as of now, so let’s go over what we do know, shall we?


As an athlete, you use glycogen (stored carbohydrates) as your main fuel. When it runs out while exercising/competing it’s known as “hitting the wall.” Avoiding this is the reason why you use energy drinks and gels – to ensure there are enough carbohydrates to fuel your performance.


If in ketosis, you wouldn’t burn glycogen, you would burn fat and ketones. This has the benefit of using less oxygen below high intensity rates (improved efficiency). It also produces less lactate.


Sounds good, right?


But when your muscles use the fat and ketones as fuel, you don’t go as fast as when you’re burning glucose and carbohydrates.


Ketosis literally affects your athletic performance for high intensity exercise.


Cyclists 300x189 - Is Keto Good For Athletes? Part 2


There seems to be a lack of performance benefits for most athletes who eat low carb, high fat diets. In fact, at least one study has shown impaired performance during high intensity workouts.


“…benefits of ketogenic dieting for performance with a high intensity component are equivocal.” (Burke, 2015)


It’s thought that this is because of how much muscles rely on glycogen, especially during intense exercise.


As exercise intensity increases, the muscles shift from getting energy from blood fats and glucose, and rely more on muscle fat and glycogen for fuel. In fact, at moderate to high intensities, muscle glycogen becomes the main source of energy.


Here is a quote from Chang, et. al, 2017:

“There is emerging evidence that [low carbohydrate high fat] LCHF diets could be beneficial, particularly for performance in ultra-endurance sports. Their effect on field-based sports that require repeated high-intensity activities is also promising. It appears that at least several months of adaptation to a LCHF diet are required for the metabolic changes and restoration of muscle glycogen to occur.”


So, what the science says so far is that ketogenic diet may help with endurance. Especially after eating this way for several months.


When it comes to high intensity workouts, some studies show promise, some show no effect, and some show impaired performance.


So, what about ketogenic supplements?


Ketogenic supplements for athletes


There is a small difference between ketosis from a ketogenic diet and ketosis from a supplement. The main difference is that, with the supplements, there would still be sugar and insulin in the blood, and glycogen in the muscles.


Ketosis from supplements does a few things:

  • Allows muscles to keep their glycogen stores;
  • Decreases lactate concentrations;
  • Increases fat oxidation.


And they seem to do this, even if you take them along with a carbohydrate supplement.


Ketone supplements show improved energy efficiency (more energy with less oxygen needed). Well, at least they do in rat hearts. However, the question remains whether this is the same for human skeletal muscle during exercise. And if it is, does this translate to more power for the same amount of oxygen consumed (i.e. improved muscle efficiency)?


We just don’t know for sure just yet.


Ketone supplement 300x300 - Is Keto Good For Athletes? Part 2


One recent study looked at two groups of cyclists who supplemented with optimal levels of carbohydrates. Some of them also incorporated a ketone supplement, and others had just the carbohydrates. The group who supplemented with both showed a small improvement in performance. They were able to go 2% farther (400 m) on average than those who only supplemented with carbs.


So, there may be some benefit to aerobic competitions when supplementing with both ketones and carbohydrates. Particularly in highly trained endurance athletes. But, this was just one small study, so more research is definitely needed.


As I mentioned earlier, there is not a lot of research just yet on the effects of keto supplements on sports performance.


“Although ketone body supplementation has been proposed to be beneficial for endurance athletes and ketone esters are speculated to be routinely used by professional cyclists, to the best of our knowledge there is currently limited information on the effects of ketone body supplementation on exercise metabolism and performance in recreational and/or elite athletes…In conclusion, based upon the few available data and our current understanding of ketone body metabolism during exercise in a sports specific setting, we conclude there is currently no evidence to support the use of ketone bodies as an ergogenic aid under conditions where optimal evidence based nutritional strategies are applied.” (Pinckaers, 2017)


So, the bottom line with keto supplements is that they may help, but we really don’t know. More research is needed.


Coffee high fat Bulletproof style 300x200 - Is Keto Good For Athletes? Part 2


The keto diet craze is here, and it may (or may not) be for you.


There are several ways to get into the state of “metabolic ketosis.” One is with the classic keto diet, or one of the three modifications you can try. And, of course, there are also ketone supplements that can get you in the state of ketosis for up to 6 hours.


The keto diet is not without risks, though. Because it is restrictive, it can result in metabolic symptoms, gastrointestinal issues, as well as nutritional deficiencies, to name a few.


As for athletes, if you’re an endurance athlete, a ketogenic diet may be beneficial. As for high-intensity, the study results really are a mixed bag.


“Unless you’re an ultra-endurance athlete, becoming fat-adapted or adopting a ketogenic diet probably won’t improve your performance.” (Precision Nutrition)


And when it comes to keto supplementation, there is a lot of speculation, and little evidence.


“Our current understanding of ketone body kinetics during exercise is insufficient to warrant their use as an ergogenic aid in any practical sports setting.” (Pinckaers, 2017)


More research is needed (and is underway).


Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, and mental health.  Follow me on Facebook, Instagram and Twitter.



Burke, L.M. (2015). Re-Examining High-Fat Diets for Sports Performance: Did We Call the “Nail in the Coffin” Too Soon? Sports Medicine (Auckland, N.z.), 45(Suppl 1), 33–49.


Chang, C.-K., Borer, K., & Lin, P.-J. (2017). Low-Carbohydrate-High-Fat Diet: Can it Help Exercise Performance? Journal of Human Kinetics, 56, 81–92.


Cox, P.J., Kirk, T., Ashmore, T et al. (2016). Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metab. 24(2), p256–268. doi: 10.1016/j.cmet.2016.07.010.


Cox, P.J. & Clarke K. (2014). Acute nutritional ketosis: implications for exercise performance and metabolism. Extreme physiology & medicine. 3(1), 1.


Evans, M., Cogan, K.E., & Egan B. (2017). Metabolism of ketone bodies during exercise and training: physiological basis for exogenous supplementation. J Physiol. 595(9), 2857-2871. doi: 10.111


Luat, A.F., Coyle, L. & Kamat, D. (2016). The Ketogenic Diet: A Practical Guide for Pediatricians. Pediatr Ann. 45(12):e446-e450. doi: 10.3928/19382359-20161109-01.


Martin, K., Jackson, C.F., Levy, R.G. & Cooper, P.N. (2016). Ketogenic and other dietary treatments for epilepsy. Cochrane.


Pinckaers, P.J.M., Churchward-Venne, T.A., Bailey, D., & van Loon, L.J.C. (2017). Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype? Sports Medicine (Auckland, N.z.), 47(3), 383–391.


Precision Nutrition, The Ketogenic Diet: Does it live up to the hype?


Schoeler, N.E. & Cross, J.H. (2016). Ketogenic dietary therapies in adults with epilepsy: a practical guide. Pract Neurol. 16(3):208-14. doi: 10.1136/practneurol-2015-001288.


Volek, J.S., Noakes, T. & Phinney, S.D. (2015). Rethinking fat as a fuel for endurance exercise. Eur J Sport Sci. 15(1), 13-20. doi: 10.1080/17461391.2014.959564.


Volek, J.S., et al. (2016). Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism. 65(3), Pages 100–110.

Comment 1

Write a comment