High-Carbohydrate, Ketogenic Diets, Exogenous Ketones: Performance and Health Effects in Endurance Athletes

Despite conventional wisdom advocating a high-carbohydrate (HC) diet, low-carbohydrate ketogenic diets (LCKD) have grown in popularity among endurance athletes in recent years. In addition, the use of exogenous ketone esters to optimise performance is an emerging area of research within sports science. Little is known about the performance and health implications of a LCKD within endurance athletes, nor an exogenous ketone esters impact on performance within well-trained runners. A non-randomised 12 week dietary and training intervention was designed to assess performance, body composition and health responses to a traditional HC and LCKD within endurance athletes. In addition, a double blind randomised crossover designed investigation was carried out to determine a ketone esters impact on exercise metabolism and endurance performance when co-ingested with carbohydrates versus a group consuming equal carbohydrates (1.2 g·min-1). A LCKD maintained 100 km time trial (TT) performance, improved body composition and relative power outputs. The LCKD caused nutritional ketosis (0.5 ± 0.4 mM beta-hydroxybutyrate (βHB)), maintained homeostatic measures of wellness, including blood lipids, glycaemic control, inflammation and oxidative stress. Nutrient analysis demonstrated HC diet was reportedly deficient in fat soluble vitamins due to restricting fat to <20% of total energy, while the LCKD was reportedly deficient in fibre (19.2 ± 4.9 g/d) and high in saturated fat (29.5 ± 9.1 %/kcal). Ketone ester ingestion caused acute nutritional ketosis (1.2 ± 0.2 mM βHB) and homogenously improved (2.9%) simulated 10 km TT running performance in well-trained athletes; despite not measurably altering metabolic or peripheral responses to submaximal exercise. In conclusion, a LCKD appears proficient at maintaining submaximal exercise performance and homeostatic measures of wellness within an endurance trained population across a 12 week intervention, while ketone ester ingestion within well-trained runners’ appears to benefit endurance performance, however, additional work is needed to determine the mechanism for improved performance.