Ketone Supplements in Athletes: Do They Work?

Ketone supplements are currently one of the “trending topics” among athletes, especially in cycling. There are many rumors indicating that these supplements are used by many of the top professional teams, treating them almost like a magic potion responsible for cyclists' success. However, this growing fame has another side, as many argue that these supplements should be banned in sports and considered doping. But do ketone supplements really work?

Evidence on ketone supplements and performance

There is some physiological basis to support the potential benefits of ketone supplements on performance. When we exercise, especially if it is high intensity, muscle glycogen is the main source of energy. However, these stores are not unlimited, and in fact their depletion is one of the main causes of fatigue (also producing the well-known “bonk”). To prevent glycogen stores from being depleted and thus have more energy, one of the main nutritional strategies is supplementation with carbohydrates during exercise (1). In this sense, theoretically ketones ingested through supplements could also serve as an “extra” energy substrate, preserving glycogen stores.

In fact, there is some scientific evidence supporting the benefits of ketone supplements. It all started in 2016, when a study published in the prestigious journal Cell Metabolism showed that supplementation with ketones reduced carbohydrate consumption during exercise, helped preserve glycogen stores, and improved performance (by 2%) in a 30-minute time trial (2). These results were and continue to be very publicized, and are frequently used to support the ergogenic effects of ketone supplements. However, many other studies on the subject have been published since then that seem to have gone unnoticed, perhaps because they did not yield such promising results. For example, one study analyzed professional cyclists who completed a 31 km time trial either taking or not taking ketone supplements, and the results showed that taking the supplement worsened performance by an average of 2% (equivalent to 1 minute) compared to the intake of a placebo substance (3). This is just one of many studies that show negative results regarding ketone supplements, and in fact, as concluded by a meta-analysis in which we combined the results of the 13 studies that had evaluated the effects of taking a ketone supplement before or during exercise, so far the existing evidence suggests that these supplements do not induce any performance benefit (4). 

Future lines of research

It is important to emphasize, however, that although the existing evidence so far seems not to support the benefits of ketone supplements, research still needs to be done. For example, most of the studies conducted to date include short-duration trials (less than 1 hour). This could be a key factor in why ketone supplements have not worked, since in high-intensity trials carbohydrates are the main energy source and therefore their inhibition when consuming ketones could have negative effects.That is why more studies are needed to evaluate the effects in long-duration tests such as ultra-endurance events, where carbohydrates play a smaller role, although the scarce evidence available so far in this regard does not seem very promising. Thus, for example, a study showed that ketone supplementation did not improve performance in a 15-minute time trial after 3 hours of cycling (5).

On the other hand, more studies are also needed to evaluate the possible benefits of ketones in post-exercise recovery. As an “extra” source of energy, if ketones are consumed after exercise along with carbohydrates, they could increase the amount of those carbohydrates used to synthesize glycogen, a key factor in recovery (6,7). In fact, preliminary evidence in humans suggests that ketone supplements could accelerate post-exercise glycogen re-synthesis (8), and although the evidence so far is limited, a recent study showed that the intake of ketones during three weeks of intense training prevented symptoms of overtraining and improved performance at the end of that period (9).However, the evidence regarding the benefits of these supplements as a method of recovery is still scarce to unanimously support their use.

Finally, one of the most important factors that must be considered when taking a supplement is its safety. Most studies have observed that ketone supplements are associated with gastrointestinal symptoms such as nausea or reflux, and in some cases vomiting and dizziness (3). However, other authors have shown that the gastrointestinal symptoms associated with these supplements may not be so prevalent and that, moreover, they depend on the type and dose of the supplement (with ketone salts producing worse symptoms than ketone esters) (10). Therefore, more evidence is needed regarding the adverse effects of these supplements, especially when consumed in large quantities and over the long term.

Conclusions

Although ketone supplements are considered by many to be the magic potion for performance in endurance athletes, so far the scientific evidence does not support the benefits of these supplements, and in fact certain studies have even found harmful effects. Surely in the coming years many more studies will come to light that will allow us to consistently conclude how recommendable these supplements can be and in what situations.

AUTHOR

Pedro Valenzuela
Researcher in the Physiology Unit of the University of Alcalá and in the Performance Control Unit at the Sports Medicine Center (AEPSAD, CAR of Madrid).
Web: www.fissac.com

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References

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2. Cox PJ, Kirk T, Ashmore T, Willerton K, Evans R, Smith A, Murray AJ, Stubbs B, West J, McLure SW, et al. Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metab [Internet]. Elsevier Inc.; 2016;24:256–68. Available from: http://dx.doi.org/10.1016/j.cmet.2016.07.010
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