Ketone bodies, namely beta-hydroxybutyrate (βHB), acetoacetate (AcAc) and acetone, are produced in the liver during physiological states and manipulations that result in reduced carbohydrate availability. Exogenous ketone supplements, namely ketone esters and ketone salts, have been developed with the aim of achieving acute nutritional ketosis i.e. βHB concentrations > 0.5 mM. We investigated whether exogenous ketone supplements had an effect on the metabolic response to exercise, physical and cognitive performance in athletes. A literature review was undertaken to examine the relationship between elevated ketone bodies, achieved via intravenous fusion of ketone bodies or fasting, and metabolism both at rest and during exercise1. The review focused on seminal work performed in the 1970s and 1980s and identified a number of metabolic effects that may have relevance to improve performance and recovery in athletic populations. Study 1 investigated the effect of a commercially-available ketone salt product formulation on the metabolic response to a graded exercise session in trained endurance athletes2. We observed an elevation in βHB concentrations (0.4-0.5 mM), a reduction in plasma glucose concentrations, but no effect on plasma lactate concentrations or exercise efficiency. Study 2 investigated the effect of co-ingestion with carbohydrate of a ketone ester supplement in the form of a (R)-3-hydroxybutyl (R)-3-hydroxybutyrate ketone mono ester on physical and cognitive performance in team sport athletes in response to a simulated soccer task3. Ingestion of the ketone ester had no effect on 15 m sprint times during the simulated task, or on reaction time or sustained attention performed afterwards. Compared to carbohydrate alone, we observed a preservation in executive function, measured by a decision making task, but a possible impairment in performance in a short high intensity intermittent performance test in the ketone ester condition. Study 3 investigated the effect in trained runners of co-ingestion with carbohydrate of a (R)-3-hydroxybutyl (R)-3-hydroxybutyrate ketone mono ester on the metabolic response to submaximal exercise, and performance in 10 km time trial and cognitive tasks. We observed no effect on endurance performance or cognitive performance with the ketone ester compared to the carbohydrate alone condition. Future research should focus on exploring the optimal dosage and timing of exogenous ketone supplements around exercise to confer performance benefits, if any. It remains to be confirmed which exercise modalities may benefit from exogenous ketone supplementation. References 1. Evans M, Cogan KE, Egan B (2017) Metabolism of ketone bodies during exercise and training: physiological basis for exogenous supplementation. Journal of Physiology 595(9):2857–71. 2. Evans M, Patchett E, Nally R, Kearns R, Larney M, Egan B (2018) Effect of acute ingestion of A-hydroxybutyrate salts on the response to graded exercise in trained cyclists. European Journal of Sport Science 18(3):376–86. 3. Evans M, Egan B (2018). Intermittent running and cognitive performance after ketone ester ingestion. Medicine & Science in Sports & Exercise 50(11):2330-2338.