Exogenous ketone esters (KE) have been proposed as supplementary fuel to increase beta-hydroxybutyrate levels in the blood. It is thought that supplemental ketone bodies may be ergogenic during prolonged endurance exercise to decrease the reliance on carbohydrate (CHO) for fuel oxidation and/or to provide an alternate fuel source if/when CHO is not available. In theory, athletes would be able to optimize utilization of CHO, fat, and these exogenous ketone bodies for performance across exercise intensities for maximum performance.
What does the research say? A recent study examined KE coadministered with CHO (KE+CHO) compared to an isocaloric CHO supplement, however the study has some limitations that make it difficult to draw meaningful conclusions. For example, the amount of CHO given was < 60 grams per hour which is lower than the recommended amount for a test protocol such as the one implemented (90 min @ 70% VO2peak followed by an incremental TTE test). Furthermore, total energy given during these trials was lower than what is recommended in a field setting at ~ 300 kcal per session and subjects completed these sessions 6 times on consecutive days. Exercise capacity was not different between KE+CHO vs CHO but insulin sensitivity appeared to decrease when KE was added. The authors suggested that KE may have a negative effect on training adaptations. It is worth noting that some studies have also observed reduced appetite following exercises after KE ingestion, adding another possible negative effect with regards to training adaptation.
When examining the current evidence in this area, the effect of acute exogenous ketone supplementation on performance remains equivocal. This is possibly due to study design (i.e. lacking strong control conditions, performance trials done in a fasted state, etc). Thus, there is not currently enough evidence to suggest that exogenous ketones can benefit performance as well as CHO does. However, we’re keeping our eyes open for any new research in the area.
PMID: 27430501, 35614576, 32735112