Abstract
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 (13)C) 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 CO(2) production and (13)C 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.