Increased Cardiorespiratory Stress During Cycling After Ketone Monoester Ingestion

Abstract

Nutritional ketosis refers to a state in which blood ketone bodies are elevated above normal basal levels, typically corresponding to a beta-hydroxybutyrate concentration ([β-HB]) of >0.5 mM. Acute ketone supplement ingestion rapidly induces nutritional ketosis without otherwise altering diet, and there is growing interest in the effect of this practice on exercise responses and performance. The limited studies to date have yielded equivocal data, likely due in part to differences in supplement type and dose, increase in [β-HB], exercise intensity, participant training status, and study blinding. Purpose: We examined the effects of a ketone monoester (KE) supplement on exercise responses and performance in endurance-trained adults (n=10 males, n=9 females; VO2peak = 57±8 ml/kg/min). Methods: Participants completed two trials in a randomized, double-blind, counterbalanced manner. A commercial KE solution (600 mg/kg body mass) or flavour-matched placebo was ingested 30 min before a 30-min cycling bout performed at individual ventilatory threshold intensity (71±3% VO2peak), followed 15 min later by a 3 kJ/kg body mass time-trial. Results: KE versus placebo ingestion increased plasma [β-HB] before exercise (3.9±1.0 vs 0.2±0.3 mM, p<0.0001, dz=3.4), mean ventilation (77±17 vs. 71±15 L/min, p<0.0001, dz=1.3) and heart rate (155±11 vs 150±11 beats/min, p<0.001, dz=1.2) during exercise, and rating of perceived exertion at the end of exercise (15.4±1.6 vs 14.5±1.2, p<0.01, dz=0.85). Plasma [β-HB] remained higher after KE vs placebo ingestion prior to the time trial (3.5±1.0 vs 0.3±0.2 mM, p<0.0001, dz=3.1) but subsequent performance was not different (KE: 16:25±2:50 vs placebo: 16:06±2:40 min:s, p=0.20; dz=0.31). Conclusion: KE supplementation, per the conditions described, increased markers of cardiorespiratory and perceived stress during submaximal exercise but did not affect time-trial performance in endurance-trained participants.