Do ketone esters spare glycogen and improve performance?

Ketones have been touted as this magic supplement that results in extra-ordinary performances. Is it really a magic bullet or is it an expensive placebo. A new study investigated.

It is possible that ketones, spare muscle glycogen and improve performance but it is also possible that ketones inhibit carbohydrate metabolism and reduce high intensity exercise performance. Neither of these theories has been tested

Studies on ketone esters so far?

Ketone supplements have received a lot of attention recently and we discussed it in this previous blog. It is important to distinguish ketone salts and ketones esters. Ketone salts can supply smaller amounts of ketone bodies without causing gastro-intestinal distress. Ketone esters are tolerated much better but are more difficult to obtain in many parts of the world and are expensive. The effects of the intake of ketone bodies are still uncertain.

Improved performance with ketone esters

One study showed a small effect on time trial performance after 1h of steady state exercise (1). The researchers observed a 2% improvement in a 30 min time trial performance. It was shown that the ketone ester caused ketosis (high ketone body concentrations in the blood) and it was suggested that this might have resulted in glycogen sparing in the muscle. Essentially the ketone bodies are a type of fat, and when that is used as a fuel, there is no need to use the precious carbohydrate stores. Glycogen sparing during the first hour, would perhaps explain the performance benefit in the subsequent time trial.

No effect on performance with ketone esters

A follow-up study (2) found no effects of ketone esters on performance and suggested that the ketone esters may not stimulate fat metabolism but inhibit carbohydrate metabolism. This inhibiting effect on carbohydrate use (glycolytic rate) could be detrimental in some situations.

Results of studies with ketone esters so far have been inconclusive

The new study

A recent study from the University of Leuven in Belgium (3) tried to get some answers.

The researchers performed a double blind placebo controlled study for which they recruited 12 cyclists and triathletes. The participants performed 2 exercise trials. Both trials consisted of a 3 hours intermittent exercise, followed by a 15 min time trial and a sprint. In both conditions, cyclists received carbohydrate during exercise (60g/h), but in once condition they also received ketone esters. The ketone esters were ingested 60 min before , 20 min before and after 30 min during exercise (25g, 20g and 20g respectively). Muscle biopsies were collected to measure muscle glycogen and performance was measured in the time trial and sprint.

What did they find?

No difference in muscle glycogen breakdown or performance were observed between the ketone ester and control treatment. If anything, glycogen breakdown was more rapid in the ketone ester trial. This means that there were neither positive nor negative effects and the study did not support the theory that glycogen was spared but it also did not find evidence for inhibition of glycolysis and negative effects on high intensity exercise performance.