Ketosis is a metabolic state similar to starvation in which energy is provided primarily by high fat intake, adequate protein intake (1 gram/Kg lean body mass) and low carbohydrate intake. The idea is to switch your body to using fat as fuel, instead of the usual carbohydrates. The keto diet has traditionally been used for weight loss, but now some athletes have taken up the diet as well. 

How does it work? 

Carbohydrates are initially restricted to 10 grams per day (15 to 20 grams per day in adolescents and adults), with patients counseled to increase their use of high fat foods (at the expense of protein). Traditionally, the diet consists of four parts fat to one part protein and carbohydrate (i.e., a 4:1 lipid to non-lipid ratio). Total calories are restricted to 80 to 90 percent of recommended values for age (Kossoff et al., 2009).  By eating a diet like this, the body becomes very efficient at utilizing fat for energy and produces higher levels of ketones (acetoacetate, acetone, and beta-hydroxybutyrate). 

What about athletes? 

Traditionally athletes have used carbohydrate sources such as maltose, dextrose, and others.  The entire industry of sports performance supplements has been geared to maximize carbohydrate absorption (max is about 240 kcals/hour due to GI function/absorption) and items are packaged in 80-100kcal/use servings.  So what happens to performance when you athletes switch to a keto diet?

Several studies have been completed looking at the short and longer (up to 3 months) use of keto-diets on performance. The results show ketosis seems to be better suited for endurance athletes than anaerobic athletes. In one study, short-term low-carbohydrate, ketogenic diets reduced exercise performance in activities that are heavily dependent on anaerobic energy systems (wroble, et al,m 2018). In another, a  low carb/keto-adaptated group of athletes had improved exercise training, lower body fat, improved fat oxidation during exercise, and better 100km time trial (McSwiney et al., 2018).

The bottom line is more research is needed, however, depending on the athletic activity, the keto diet may either help or harm athletic performance.

Contraindications: Individuals with inborn metabolic errors should NOT use the ketogenic diet.  Individuals with a history of documented myopathy or rhabdomyolysis should complete a more in depth workup for inborn errors prior to starting a ketogenic diet due to an increased risk of catabolic crisis.

References

• Kossoff, E. H., Zupec-Kania, B. A., Amark, P. E., Ballaban-Gil, K. R., Christina Bergqvist, A. G., Blackford, R., Buchhalter, J. R., Caraballo, R. H., Helen Cross, J., Dahlin, M. G., Donner, E. J., Klepper, J., Jehle, R. S., Kim, H. D., Christiana Liu, Y. M., Nation, J., Nordli, D. R., Jr, Pfeifer, H. H., Rho, J. M., Stafstrom, C. E., … International Ketogenic Diet Study Group (2009). Optimal clinical management of children receiving the ketogenic diet: recommendations of the International Ketogenic Diet Study Group. Epilepsia, 50(2), 304–317. https://doi.org/10.1111/j.1528-1167.2008.01765.x
• Wroble, K. A., Trott, M. N., Schweitzer, G. G., Rahman, R. S., Kelly, P. V., & Weiss, E. P. (2019). Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial. The Journal of sports medicine and physical fitness, 59(4), 600–607. https://doi.org/10.23736/S0022-4707.18.08318-4
• McSwiney, F. T., Wardrop, B., Hyde, P. N., Lafountain, R. A., Volek, J. S., & Doyle, L. (2018). Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes. Metabolism: clinical and experimental, 81, 25–34. https://doi.org/10.1016/j.metabol.2017.10.010