Update on the Acute Effects of Ketone Supplements in Athletes

Dear Editor:

We have read with interest the study entitled “Utility of ketone supplementation to enhance physical performance: a systematic review” (1), where Margolis and O'Fallon summarize the evidence on the potential ergogenic effects of ketone supplements and nicely discuss potential biological mechanisms. The authors conclude that there are discrepancies across studies in the effects of ketone supplements on exercise performance (1). Based on this heterogeneity, they conclude that there is currently insufficient evidence to support a recommendation of using ketone supplements for athletes. It must be noted, however, that the authors reviewed at the same time the effects of chronic (i.e., several weeks) and acute (i.e., before exertion) administration of ketone supplements on sports performance.

From the 3 studies (2–4) considered as “positive” for athletic performance by Margolis and O'Fallon, only the study by Cox et al. (3) actually reported a significant improvement in performance with acute ketone supplementation. The study by Waldman et al. (4) did not find an enhanced performance after acute ketone supplementation. Although these authors reported an increased fatigue index (i.e., a lower reduction of power output per unit of time) during the Wingate anaerobic test, no improvements were found for actual performance (as reflected by the lack of differences for peak and mean power output during the test) (4). In turn, the performance benefits reported by Poffé et al. (2) were found after 3 wk ketone supplementation, but no acute effects were observed. Therefore, acute ketone supplementation does not improve exercise performance, at least in efforts lasting ≤1 h. In fact, a recent meta-analysis by our group—including 13 studies in total—found that acute ketone supplementation exerts no effects on overall performance (Hedges’ g = −0.05; 95% CI: −0.30 to 0.20; P = 0.682) (5). The lack of performance-enhancing effect was confirmed when analyzing separately endurance time-trial performance (Hedges’ g = −0.04; 95% CI: −0.35 to 0.28; P = 0.820), the effects of ketone esters (Hedges’ g = −0.07; 95% CI: −0.38 to 0.24; P = 0.660), or those of ketone salts (Hedges’ g = −0.02; 95% CI = −0.45 to 0.41; P = 0.928). Of note, no heterogeneity was found for any of these results (I² = 0%) (5). Except for the study by Cox et al., the rest of the available reports to date have found no benefits of acute ketone supplementation or even negative effects on athletic performance (6, 7).

Future studies should analyze the acute effects of ketone supplements on other types of exercise (e.g., ultra-endurance sports), and further research is warranted to confirm its potential benefits as a recovery drink or when consumed in the longer term—such as in the study by Poffé et al. (2). For the time being, there is insufficient evidence to recommend acute supplementation with ketone supplements in athletes.

Notes

The authors’ responsibilities were as follows—PLV: conceived the original idea and drafted the initial version of the manuscript; AC-G, JSM, and AL: revised the manuscript and contributed with important intellectual content; and all authors: are responsible for the final content and read and approved the final manuscript.

Supported by University of Alcalá grant FPI2016 (to PLV).

Author disclosures: The authors report no conflicts of interest.