The ketogenic diet has become the latest, most media loved diet fad. Last year the phrase, “ketogenic diet” was the second most searched term on Google in the health category. Endurance athletes are particularly intrigued with this diet. The promise of losing weight, increasing lean body mass and improving endurance performance seems almost too good to be true. The ketogenic diet fad is also being driven by a number of high profile athletes who claim, through personal experience, that it dramatically improves endurance performance.
The core of the diet is to reduce carbohydrate consumption to less than 50 grams a day. At that point, your body goes into ketosis thereby burning ketones or fat for energy. The endurance benefit comes from the fact your body is now drawing on larger energy reserves. The average athlete's muscles store about 1,700 calories in the form of glycogen. However, under the ketogenic diet your body theoretically is pulling on fat stores. Each pound of fat contains about 3,500 calories and even the leanest athlete has a number of pounds of fat. Thus your muscles now tap into a bigger energy reserve. It has also been suggested that a ketogenic diet promotes adaptations that improve endurance. Can the ketogenic diet provide all these benefits?
This Performance Tip, as well as next week's, will examine the reported data. In a recent article, scientists from Tufts University reviewed the peer-reviewed studies to date. They specifically focused on whether the ketogenic diet impacted VO2Max when compared with a standard carbohydrate diet. VO2Max is the gold standard for endurance performance. They also looked at other parameters, such as time to exhaustion and RPE (ratings of perceived exertion) which is a measure of how fatigued one feels during and after exhaustive exercise. In the majority of the studies, there was no difference between the ketogenic diet and a conventional carbohydrate one. The scientists suggested that other factors such as genetics may play a role in determining whether the ketogenic diet improves endurance performance. However, it is clear based on this report, that the ketogenic diet is not the "magic bullet" it is purported to be. Next week's Performance Tip highlights a well-controlled comparative study, which further undermines the claims made by enthusiasts of the ketogenic diet.