Ketone ester ingestion increases exogenous carbohydrate storage and lowers glycemia during post-exercise recovery: a randomised crossover trial

β-hydroxybutyrate can suppress endogenous glucose production, with potential implications for carbohydrate metabolism during post-exercise recovery. The aim of the current study was to assess the effects of ketone ester ingestion during post-exercise recovery, on carbohydrate metabolism and subsequent exercise capacity. Thirteen endurance-trained men (age: 18-61 years, maximal aerobic capacity: 50 to 73 mL kg^-1 min^-1) completed two conditions in a randomized crossover design. During both conditions, participants performed two exhaustive bouts of running separated by 4 h of recovery, during which they ingested sucrose (1 g kg^-1 h^-1 and high natural abundance ¹³C) and whey protein (0.4 g kg^-1 h^-1) beverages. In one condition, the beverage was supplemented with 0.29 g kg^-1 h^-1 of ketone monoester (KETONE), in the other, the beverage was supplemented with an isoenergetic (fat), taste-matched placebo (PLACEBO). Breath samples were analysed for CO₂ production and ¹³C enrichment to determine the fate of ingested carbohydrate. Blood was sampled to examine metabolite and insulin concentrations. KETONE increased blood β-hydroxybutyrate concentrations (> 3.5 mmol L^-1 versus PLACEBO, p < 0.0001) and retention of ingested sucrose (from 206 ± 26 g with PLACEBO to 220 ± 26 g with KETONE, p = 0.001) while lowering glycemia (> 1 mmol L^-1 versus PLACEBO, p < 0.0001). This occurred with no evidence of increased gastrointestinal distress during recovery, but mild additional lower gastrointestinal distress during the second run (p = 0.03). There was no evidence for differences in time-to-exhaustion during the second run (PLACEBO:54 ± 33 min, KETONE:52 ± 28 min; p = 0.87). In conclusion, ketone ester ingestion during post-exercise recovery augments retention of ingested carbohydrates and lowers glycemia. No evidence for increased exercise capacity was detected during subsequent running.