Ketone supplements, used by some athletes seeking a competitive advantage, may in fact worsen performance, according to Canadian researchers.
Trained endurance cyclists who drank a ketone supplement before taking part in time trials sustained lower speeds compared with those who consumed a placebo, according to the study, which was published in the International Journal of Sport Nutrition and Exercise Metabolism.
“One of the main perceived benefits is that ketones may serve as an alternative fuel source during exercise or potentially alter the utilisation of other major fuel such as carbohydrates and fats, and in turn enhance endurance capacity,” said supervising author Professor Martin Gibala, from the Department of Kinesiology at Ontario's McMaster University. “But our findings suggest that isn’t the case.”
Natural ketones can serve as fuel for the brain and muscles. A ketogenic diet – characterised by very low carbohydrate and typically high fat intake – shifts the metabolism into a state of ketosis, where the abundance of ketones is greater than the use of ketones by the body. Ketosis is also achieved during fasting or strenuous exercise.
Ketone supplements supposedly speed up that process, without the strict diet.
Previous findings related to the effectiveness of ketone supplements have been contradictory; despite some studies showing them to improve athletic performance, others have found they have no effect or even worsen performance.
For this double-blind study, researchers recruited trained endurance athletes who cycled for five or more hours per week, the idea being that their athletic performance would remain consistent from day to day.
The experiment was conducted in a laboratory but simulated race conditions. Subjects drank either a ketone supplement or placebo before completing a 20-minute cycling time trial that acts as a close predictor of 40km race performance.
They produced about 2 per cent less power after drinking the ketone beverage compared with the placebo, which would translate into a significantly slower race time.
“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,” said lead author Devin McCarthy, a graduate student in McMaster’s Department of Kinesiology.
The researchers said their findings align with their previous work that found ketone supplements increased cardiorespiratory stress during exercise.
They are currently investigating responses to varying doses of the supplements at different exercise intensities to better understand how ketones may affect performance, and the potential underlying mechanisms.
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