Do Ketogenic Diets Reduce Anaerobic Performance?

Evan Stevens

Ketogenic diets have come to the forefront of popular health fads in the past few years. Placing the majority of our health and dietary problems on carbohydrates (due to the spike in blood glucose followed promptly by the spike in insulin, which if done continually can lead to a host of health issues such as diabetes and circulation issues), ketogenic diets place an emphasis on restricting and eliminating most carbs from the diet and replacing them with fats. The body normally prefers to use carbohydrates for energy but when there is a lack of carbs available, the body will produce ketones. Ketones are produced by fats in the liver to help the body survive when food intake is low. Ketogenic diets force the body into this metabolic state not through starvation of calories but through starvation of carbs. By producing ketones for energy, you can avoid some of the harmful outcomes of repeated, high sugar challenges to your metabolic system.

How Does the Diet Affect Athletes?

However, athletes who are worried about their diets should look away from the ketogenic diet, at least if you are a high-intensity, shorter interval type athlete (a HIIT-type athlete). A recent, smaller study from Saint Louis University looked at the effect of ketogenic diets on exercise performance in 16 men and women and found that ketogenic diets significantly decreased performance in activities relying on the anaerobic system. The study had the participants follow either four days of high carbohydrate or four days of a high fat, low carbohydrate ketogenic diet (<10% daily energy from carbs) after which the participants were required to perform a Wingate cycling and a yo-yo intermittent recovery test (similar to the classic beep test but with a little more recovery time between levels; it is a highly popular tool to study pure HIIT outcomes).

The researchers found that the ketogenic diets reduced the peak power output by 7% and the mean power output by 6% in the Wingate test and that the ketogenic diet reduced the total distance run in the yo-yo intermittent recovery test by 15%. These findings suggest that short-term ketogenic diets reduce anaerobic and repeated HIIT-type exercise performances. While some arguments might be made about the time scale and adaptations to the diet, there is also more that can be said about how performance metabolism functions and the reason ketogenic diets have come up a lot in popular health discussions.

But at What Cost?

An average, normal diet is made up of 60% carbohydrate. If we eliminate that, it is very difficult to make up the calorie deficit with fats and proteins alone. So what often happens is that we are reducing overall calories and not just eliminating carbs. When we eliminate calories we often see weight loss, which is possibly the biggest reason why ketogenic diets are so popular today. Athletes looking to get an edge up on the competition through proper diet will want, and probably need, to look elsewhere to meet the energy demands of their sport, but even in the general population ketogenic diets can have some off-putting side effect.

While the affected system is anaerobic, and many may think that it doesn’t apply to them in their daily lives, the anaerobic system is the same one we use to go up the stairs, run around the backyard with our kids or run to make the bus. Every day people use this system without really realizing it. Ketogenic diets have shown to be useful in individuals with epilepsy or abnormal cell metabolism but for most people, the diet is a simple caloric restriction and for athletes, it could be harmful to performance.

Recap

Ketogenic diets consist of trying to reduce or eliminate carbs from the diet (carbs making up less than 10% of daily caloric intake).
Ketogenic diets hurt anaerobic performance with reducing peak and mean power in Wingate tests and reducing the total distance ran in yo-yo intermittent recovery running tests.
- Ketogenic diets are harmful to anaerobic and HIIT athletic performances.
Ketogenic diets may be good for weight loss and for certain diseases but for the general population, it may come with unwanted side effects.

Citations

Kymberly A. Wroble, Morgan N. Trott, George G. Schweitzer, Rabia S. Rahman, Patrick V. Kelly, Edward P. Weiss. 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, 2018

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