Ketone ester supplements continue to receive attention from athletes for their claimed potential to enhance endurance exercise performance. The basis of this interest stems from being able to drink this supplement and quickly induce ketosis (high blood levels of ketone bodies) without the need to restrict dietary carbohydrate (for example, adhering to a ketogenic diet). It is becoming increasingly clear that ketone supplements influence exercise responses, however scientists still do not fully understand how.
Mixed findings for ketone supplements and performance
Some research concerning ketone supplements has previously been covered, including the effects on glycogen sparing, ketones as a metabolic fuel, and recovery from exercise. This blog post will cover a recent study led by McCarthy and colleagues from McMaster University in Canada that attempted to clarify whether drinking a ketone ester before a performance test could in fact influence cycling performance (1).
The performance hype surrounding ketone supplements stemmed from a study published in 2016 that examined the effects of drinking a newly developed ketone supplement (called a ketone monoester) before a 1 hour cycling bout and subsequent 30-min time-trial (2). This study reported a ~2% improvement in time-trial performance after drinking the ketone ester compared to a placebo beverage. Since this publication, many research studies have tested the performance effect of ketone supplement ingestion. The results of such have been mixed with a few even reporting that endurance performance was impaired when athletes used the exogenous ketone supplement before the performance test.
Some authors speculated that the different performance observations were due, at least in part, to exogenous ketone supplement type… ketone monoesters could make you faster, but ketone diesters and salts caused gastrointestinal (GI) discomfort and made you slower!Other authors speculated that the dose of the exogenous ketone supplement was important such that too small a dose would not do anything, yet too large a dose would elicit consequences that offset the benefits.
New study on ketone supplements
These two areas – supplement dose and supplement type – were considerations that this new study attempted to address. In the study by McCarthy et al., the correct supplement (ketone monoester) was ingested by trained cyclists in such a dose that was neither too low nor too high.
This study was designed to be deliberately simple: participants arrived at the lab after eating what they would normally do before this type of performance test, ingested either a specific dose of the ketone monoester supplement or a flavour-matched placebo, waited 30 minutes for the supplement to be digested, then did a warmup and 20-min time-trial on a cycle ergometer. A 20-min time-trial is highly predictive of functional threshold power, a class cycling performance metric. Both the participants and researchers were unaware of what drink was ingested on a given trial day.
A blood sample before the performance test confirmed that blood ketone body levels were in the purported optimal range, that is, high enough but not too high. A questionnaire demonstrated that gastrointestinal (GI) symptoms were slim-to-none. However, participants performed on average ~2% worse in the performance test the day they drank the ketone monoester supplement compared to the day they received the placebo. In other words, the athletes performed better when they drank the placebo control drink!
Participants performed ~2% worse with the ketone monoester supplement compared to the control trial.
Possible explanations for impaired performance with ketone supplements
Scientists are still unsure as to why ketone monoester supplements may impair performance during certain cycling tests. It may be that blood acid-base balance is disturbed by ketone supplement ingestion, an effect that researchers have long linked to performance outcomes. Others have shown it could be that exogenous ketone supplements increase perception of effort and heart rate for a given cycling workload.
Another important consideration when assessing whether athletes could benefit from using exogenous ketone supplements is the characteristics of the performance test. The study covered in this article showed that performance was worse in a high intensity short duration test, however this does not exclude possible effects of exogenous ketones in lower intensity longer duration events. We do not know how ketone supplements affect lower intensity longer duration tests, but future research studies could address this question.
In addition to the type of the exercise being important, whether the supplements are ingested before or after exercise is also important. Emerging data suggest that the greatest benefit of these supplements to athletes may be drinking them after strenuous exercise, i.e., recovery, or during exposure to low oxygen environments, i.e., altitude.
Summary
To summarise, the study by McCarthy et al. showed clear evidence that ketone monoester supplement ingestion did not benefit cyclists during a 20-min time-trial. However, the story of exogenous ketone supplements is not yet complete and there are many emerging and exciting contexts which these supplements may be used.
If you are interested in learning more about ketone supplements and athletic performance, click below for a talk by Prof Javier Gonzalez on Ketones.
References
McCarthy DG, Bone J, Fong M, Pinckaers PJM, Bostad W, Richards DL, van Loon LJC, Gibala MJ. Acute Ketone Monoester Supplementation Impairs 20-min Time-Trial Performance in Trained Cyclists: A Randomized, Crossover Trial. Int J Sport Nutr Exerc Metab. 2023 Apr 25;33(4):181-188. doi: 10.1123/ijsnem.2022-0255.
Cox PJ, Kirk T, Ashmore T, Willerton K, Evans R, Smith A, Murray AJ, Stubbs B, West J, McLure SW, King MT, Dodd MS, Holloway C, Neubauer S, Drawer S, Veech RL, Griffin JL, Clarke K. Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metab. 2016 Aug 9;24(2):256-68. doi: 10.1016/j.cmet.2016.07.010. Epub 2016 Jul 27.
