A Dietitian's Perspective on the Ketogenic Diet: Athletic Nirvana or Nutrition Quackery?
The ketogenic diet has emerged into the athletic world as the new way to increase your body’s fat burning capabilities, along with the claims that it increases performance among endurance athletes (1). While the ketogenic diet (and other forms of prolonged fasting) were historically used to treat epilepsy (2), today, this diet has gained popularity in competitive sports and for everyday active people.
What is a ketogenic diet? A ketogenic diet is essentially a diet that is high in fat (50% or more of your total daily calories), and very low in carbohydrates, (less than 20% of your total daily calories), and variable amounts of protein (1). While various foods can be consumed when following a ketogenic diet, items such as full-fat dairy products, eggs, meats, oils and butter are common due to their high-fat content (2).
With the low amount of carbohydrates available for energy, the body switches over from its normal metabolism of using glucose for fuel, to the state of ketosis, which is where the liver incompletely oxidizes fat into substances known as ketone bodies, (including 3-hydroxybutyrate, acetoacetate and acetone). These ketone bodies are then used as a fuel source for your body instead of glucose (1).
To better understand if there is credible scientific research to support the benefits of the ketogenic diet for athletes, I searched the scientific literature to determine what we currently know about the benefits of this diet. Here is what I found:
One study showed that male endurance athletes who followed a ketogenic diet decreased body mass and percentage body fat, when compared to another group of endurance athletes who consumed a high carbohydrate diet for 12 weeks. Although differences in body mass and body fat were observed between the groups, the ketogenic diet group did not show improvements in athletic performance in all events tested (3).
A recent review paper of low-carbohydrate and high-fat diets published by Chang, Borer, and Lin described that low carbohydrate and high fat diets may help to control body weight and fat mass while maintaining lean body mass in some athletes who participate in weight-sensitive sports (1).
In a 10-week pilot study in endurance athletes from New Zealand, those who followed the ketogenic diet reduced body weight, and decreased time to exhaustion in endurance events (4).
At this time, it seems that the research is limited to short-term studies, some of which, do show a benefit of following a ketogenic diet for weight loss and body composition, but not consistently for improved athletic performance. Ultimately, many questions about the benefits of the ketogenic diet for athletes remain. For example, what are the health effects of following a ketogenic diet in the long-term? Is it sustainable for endurance athletes beyond a trial period? If you are an athlete who has another health condition, is following the ketogenic diet right for you? What nutrient deficiencies will athletes experience by restricting all carbohydrates from their diet?
My hope is that research continues to build in this area, so that we can answer these remaining questions for athletes. If you are already following a ketogenic diet or considering it, my recommendation is to talk to your healthcare provider before trying it out on your own. Working with a registered dietitian (RD) alongside your medical doctor or healthcare practitioner will ensure that you are planning and following a balanced diet to help you achieve your goals.
*Thank you to dietetic intern Morgan Entinger for helping with the content for this article.
Chang, C.-K., Borer, K., & Lin, P.-J. (2017). Low-Carbohydrate-High-Fat Diet: Can it Help Exercise Performance? Journal of Human Kinetics, 2017; 56: 81–92. http://doi.org/10.1515/hukin-2017-0025.
Roehl, K., Sewak, S. (2017) Practice Paper of the Academy of Nutrition and Dietetics: Classic and Modified Ketogenic Diets for Treatment of Epilepsy. Journal of the Academy of Nutrition and Dietetics, Volume 117, Issue 8, 1279 – 1292.
McSwiney, F.T., Wardrop, B., Hyde, P.N., Lafountain, R.A., Volek J.S., Doyle, L. (2017) Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes.
Zinn C et al. 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. 2017 Jul 12;14:22. doi: 10.1186/s12970-017-0180-0. eCollection 2017.