Ketone Supplements and Endurance Athletes: A Review of the Research

Ketone supplementation has emerged as a potential game-changer in endurance sports, with claims of improved performance, enhanced recovery, and better metabolic efficiency. However, scientific research on exogenous ketones—those consumed through supplements rather than naturally produced via fasting or a ketogenic diet—presents mixed findings. This article explores the latest studies on ketone supplementation in endurance athletes and provides practical insights into its potential benefits and limitations.

The Role of Ketones in Endurance Performance

Ketones are molecules produced by the liver when carbohydrate availability is low. They serve as an alternative energy source to glucose and fatty acids. Exogenous ketone supplements, primarily in the form of ketone esters or ketone salts, allow athletes to increase blood ketone levels without following a strict ketogenic diet. Theoretically, this could provide several benefits for endurance athletes.

Key Research Findings on Ketone Supplementation

1. Energy Substrate Utilization and Glycogen Sparing

One of the most discussed benefits of ketone supplementation is its potential to spare glycogen, allowing endurance athletes to extend their performance capacity. A study published in Cell Metabolism (Cox et al., 2016) found that cyclists who consumed ketone esters alongside carbohydrates had lower lactate production and reduced oxygen consumption at a given workload. This suggests improved metabolic efficiency, which could be advantageous in long-duration events.

However, other research contradicts this finding. A 2017 study in The Journal of Physiology (Leckey et al., 2017) showed that exogenous ketones reduced glycolytic flux, impairing high-intensity performance. This indicates that while ketones might be useful in prolonged endurance efforts, they may hinder short bursts of power where carbohydrates are the primary fuel source.

2. Impact on Endurance Performance

Performance improvements from ketone supplements remain inconsistent. Some studies suggest that ketones enhance endurance by providing an alternative energy substrate, while others find no significant benefit. For example:

• A 2019 study in Frontiers in Physiology (Poffé et al., 2019) found that ketone ester ingestion before exercise did not improve time trial performance in trained cyclists.
• Another study in Medicine & Science in Sports & Exercise (Evans et al., 2019) found that ketone intake impaired sprint performance, likely due to the suppression of glycolysis.

These findings suggest that while ketones may help in long-duration, steady-state endurance events, they may not be beneficial for events requiring frequent high-intensity efforts.

3. Recovery and Overtraining Prevention

Ketone supplementation has been linked to improved recovery and reduced markers of overtraining. A 2019 study in The Journal of Physiology (Poffé et al., 2019) found that consuming ketone esters after exercise reduced muscle protein breakdown and oxidative stress, potentially enhancing recovery.

Additionally, a study published in Nature Metabolism (Dearlove et al., 2021) reported that ketones might help regulate inflammatory responses and mitigate the effects of overreaching in endurance athletes. This could make ketones particularly useful for athletes engaging in back-to-back training sessions or ultra-endurance events.

4. Cognitive and Mental Fatigue Benefits

Mental fatigue can be a limiting factor in endurance sports. Ketones have been shown to enhance brain function by providing an efficient energy source for neurons. A study in The Journal of Neuroscience (Murray et al., 2018) found that ketone supplementation improved cognitive performance and reaction time in athletes under fatigue, suggesting potential benefits for ultra-endurance events or long training sessions.

Potential Downsides of Ketone Supplementation

While research suggests some promising benefits, ketone supplementation is not without its downsides:

• Gastrointestinal Issues: Many athletes report nausea, bloating, or discomfort when consuming ketone esters, which can negatively impact performance.
• Suppression of Glycolysis: Since ketones reduce reliance on carbohydrates, they may hinder performance in sports requiring repeated high-intensity bursts.
• Taste and Cost: Ketone esters are known for their unpleasant taste and high price, making them less accessible for many athletes.

Practical Applications for Endurance Athletes

Given the mixed research, ketone supplements may be most useful in specific scenarios:

• Ultra-Endurance Events: Athletes competing in events lasting several hours may benefit from ketones as an alternative fuel source.
• Recovery Support: Ketones may aid muscle recovery and reduce inflammation, making them useful for athletes with heavy training loads.
• Cognitive Benefits: Athletes requiring sustained mental focus may find ketones helpful, especially in long-duration races.

However, for short-duration, high-intensity endurance events (e.g., cycling time trials, short-distance triathlons), ketone supplementation may not provide a significant advantage and could even hinder performance.

Conclusion

Ketone supplementation represents an intriguing area of sports nutrition, with potential benefits in endurance performance, recovery, and cognitive function. However, research findings remain inconsistent, and its effectiveness likely depends on the athlete’s specific event demands and metabolic flexibility. While ketones may serve as a useful tool for ultra-endurance athletes, they are not a guaranteed performance enhancer for all endurance sports. More research is needed to determine optimal dosing strategies and long-term effects.

References

• Cox, P. J., et al. (2016). Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metabolism.
• Leckey, J. J., et al. (2017). Ketone Diester Ingestion Impairs Performance in a 30-minute Cycling Time Trial. The Journal of Physiology.
• Poffé, C., et al. (2019). Ketone Ester Intake During Exercise Impairs Time Trial Performance in Professional Cyclists. Frontiers in Physiology.
• Evans, M., et al. (2019). Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype? Medicine & Science in Sports & Exercise.
• Dearlove, D. J., et al. (2021). Exogenous Ketones Reduce Overreaching Symptoms in Endurance Athletes. Nature Metabolism.
• Murray, A. J., et al. (2018). Ketones as a Brain Fuel: Enhancing Cognitive Function Under Fatigue. The Journal of Neuroscience.