Can Exogenous Ketones Give You the Edge? Spoiler Alert: Probably Not
The world of endurance sports is constantly searching for ways to improve performance. In recent years, one potential performance booster has gained significant attention: exogenous ketones. But before you rush out and buy the latest ketone supplement, let's delve into the science and see if ketones actually deliver.
What are Ketones and How Do They Work?
Our bodies naturally produce ketone bodies during periods of low carbohydrate availability, such as when following a ketogenic diet or during prolonged fasting. These ketone bodies, primarily beta-hydroxybutyrate, acetoacetate, and acetone, serve as an alternative fuel source for the brain, heart, and skeletal muscle when glucose (blood sugar) is scarce.
The Allure of Exogenous Ketones: A Glucose-Sparing Hypothesis
Previous research suggests that a ketogenic diet might hinder endurance performance due to the limited availability of glucose, the primary (and most efficient!) fuel source for muscles during exercise. Enter exogenous ketones – supplements designed to elevate blood ketone levels without restricting carbohydrates. It has been hypothesized that by providing an alternative fuel source in the form of exogenous ketones, athletes could "spare" their glucose stores, potentially extending the amount of time their glucose stores last and delaying fatigue.
Examining the Evidence: A Systematic Review and Meta-Analysis
A 2022 study published in the International Journal of Sport Nutrition and Exercise Metabolism [1] aimed to shed light on this question. The researchers conducted a systematic review and meta-analysis, a powerful research approach that analyzes data from multiple studies to draw stronger conclusions.
Methods:
The review searched through 569 studies, focusing specifically on those that:
Used ketone monoesters and ketone precursors, the supplement types known to be most effective in raising blood ketone levels.
Investigated running or cycling performance.
Employed a randomized controlled trial design, ensuring a high degree of scientific rigor.
Ultimately, 8 studies met the inclusion criteria, with a total of 80 participants (mostly men).
Ketone supplement dosages ranged from 500 to 922 mg/kg body weight.
Both nutritive (containing carbohydrates) and non-nutritive control groups were used for comparison.
Exercise durations varied from 80 to 195 minutes of running or cycling.
Results:
The analysis delivered a clear message: there were no significant differences in overall endurance performance between the ketone supplement and control groups. This means that despite reaching a state of ketosis (indicated by blood beta-hydroxybutyrate levels exceeding 0.2 mM), exogenous ketone supplementation did not translate to improved performance in runners and cyclists.
Furthermore, the study found no correlation between blood ketone concentration and exercise performance. In simpler terms, having higher levels of ketones in the bloodstream didn't necessarily equate to better performance.
Adding a further layer of concern, gastrointestinal (GI) symptoms were reported by the ketone supplement group in 7 out of the 8 studies. This suggests that ketone supplements might cause digestive discomfort for some athletes, potentially hindering performance rather than enhancing it.
Discussion and Conclusion:
While the concept of exogenous ketones offering a performance advantage is intriguing, the current research paints a different picture. Based on this meta-analysis, including only 8 studies with limitations in methodology and participant demographics, there's no compelling evidence to suggest that ketone supplements improve endurance performance in trained athletes.
Where to From Here?
The exploration of exogenous ketones in sports nutrition is ongoing. Here are some key takeaways to consider:
Limited Research: Currently, the evidence pool is relatively small. More studies with robust methodologies and larger participant groups are needed to draw definitive conclusions.
Individual Variability: Even if future research reveals some benefit to exogenous ketones, it's important to remember that individual responses can vary. What works for one athlete might not work for another.
Focus on the Basics: For most athletes, prioritizing a balanced diet with adequate carbohydrate intake, proper hydration, and a well-structured training plan will continue to be the cornerstone of optimizing endurance performance.
The Bottom Line:
Currently, the science suggests that exogenous ketone supplements are unlikely to be the magic bullet for boosting endurance performance. Endurance athletes should stick with a well-established strategy—a balanced diet rich in carbohydrates—as this remains the most effective approach to ensure high carbohydrate availability and lasting fuel sources during training and competition.
Brooks, E., Lamothe, G., Nagpal, T. S., Imbeault, P., Adamo, K., Kara, J., & Doucet, É. (2022). Acute Ingestion of Ketone Monoesters and Precursors Do Not Enhance Endurance Exercise Performance: A Systematic Review and Meta-Analysis. International Journal of Sport Nutrition and Exercise Metabolism, 32(3), 214-225.