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Short-term keto diets and athletic power

Keto diets can help athletes shed weight quickly. But do they also shed performance?

Study under review: Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial

Introduction

Ketogenic (keto) diets are generally defined[1] as those in which carbohydrate intake is restricted to less than 50 grams per day in order to move the dieter’s metabolism toward a greater reliance on fat[2] for fuel. This metabolic shift is preceded by near depletion of liver glycogen. Muscle glycogen and its accompanying stored water[3], will also be reduced, especially when a ketogenic diet is combined with exercise, which manifests as rapid bodyweight loss over the first several days. Athletes in weight class-controlled[4] sports take advantage of the rapid decrease in body water to make weight before competition.

While this keto diet-induced metabolic shift to favor fat metabolism may be theoretically beneficial for some athletes, reduction of glycogen stores may negatively impact high-intensity performance. But that’s not the only reason why low-carb keto diets could affect performance. As you can see in Figure 1, the production of ketones also comes along with acid (hydrogen ions, aka H+) production, which could induce fatigue[5]. Since high-intensity exercise also generates hydrogen ions, a keto diet may exacerbate these effects.

While the impact of keto diets is a growing area of research, few studies have evaluated the effect of very short-term diets on intermittent performance and power output. To meet the need for this type of research, the study under review evaluated the connection between acidification and power performance following a short-term ketogenic diet.

Ketogenic diets are based on very low carbohydrate consumption, which may generate acid. This may negatively impact higher intensity and intermittent performance, which is relevant for athletes who use crash keto diets to make weight for a competition. The study under review explored short-term keto diets, acidity, and power performance.

Who and what was studied?

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Other Articles in Issue #44 (June 2018)