Ke-don’t? Endurance athletes actually perform worse after taking ketone supplements

HAMILTON, Ontario — More and more competitors, particularly endurance athletes, are turning to ketone supplements in hopes of improving their performances and speed. Now, however, researchers from McMaster University suggest that these supplements may actually worsen athletic performances.

Ketones are chemicals produced by the liver by breaking down fat. Normally, when we’re eating regularly, our bodies have enough insulin to convert sugar (glucose) into energy. However, when we’re low on insulin (while fasting, for example) the liver will turn fat into ketones and send them into the bloodstream, where they serve as fuel for the brain and muscles.

In recent years, ketogenic diets, characterized by little to no carbohydrates and high fat intake, have seen a major boost in popularity among people losing weight. This development has given rise to ketone supplements that claim to help speed up the ketogenic, fat-burning process — all without the need to follow a strict diet.

This latest project tackles the topic of ketone supplements, attempting to gain some clarity on a subject that has yielded inconclusive results thus far. This isn’t the first study to assess such supplements’ efficacy, but earlier projects have contradicted each other. Some have found ketone supplements improved performance, while others have noted they had no effect or even a negative impact.

“One of the main perceived benefits is that ketones may serve as an alternative fuel source during exercise or potentially alter the utilization of other major fuel such as carbohydrates and fats, and in turn enhance endurance capacity,” says Martin Gibala, supervising author of the study and a professor in the Department of Kinesiology at McMaster University, in a media release. “But our findings suggest that isn’t the case.”

Weight loss and diet pills or supplements
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The research team recruited a group of well-trained endurance athletes who had been habitually cycling five or more hours per week. This group was chosen in particular because of their consistent athletic performances on a daily basis. The experiment was held in a lab setting with simulated race conditions, but participants prepared as they normally would for any other real cycling competition.

Each athlete completed two trials that differed in just one way — the drink they received beforehand. Those 20-minute cycling time trials closely predicted 40-km race performance, and the drinks contained either a ketone supplement or a similar-tasting placebo.

This project was put together as a double-blind study, meaning neither the researchers nor the athletes were aware of which drinks were really ketone supplements and which were placebos.

“The main observation from this study was that the speed that the cyclists could sustain during the test was lower after drinking the ketone supplement compared to the placebo,” explains Devin McCarthy, lead author of the study and graduate student in the Department of Kinesiology at McMaster.

Study authors add that these conclusions match up nicely with their previous work that had found ketone supplements increased cardiorespiratory stress while exercising. Moving forward, they are currently investigating responses to varying doses of the supplements at different exercise intensities in an attempt to form a clearer understanding of how ketones may or may not affect performance, as well as the potential underlying mechanisms.

The study is published in International Journal of Sport Nutrition and Exercise Metabolism.

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