Exercise responses to exogenous ketone supplementation in humans: physiology, metabolism, and performance

Abstract

Ketone bodies (KB) are biologically active compounds that are increased during prolonged periods of carbohydrate restriction, e.g., in response to a ketogenic diet or after fasting. Ingestion of KB supplements is a novel method to study the effect of acutely increasing blood KB concentrations without changing diet. This thesis examined physiological, perceptual, and performance responses to acute hyperketonemia or elevated blood KB in humans. Studies 1 and 2 involved ingestion of 0.6 g/kg body mass of a commercial ketone monoester (KE) supplement 30 minutes before a 30-minute cycling bout at an intensity corresponding to ventilatory threshold. KE compared to placebo ingestion increased blood KB concentrations and decreased pH during exercise. Study 1 found that heart rate, ventilation, and rating of perceived exertion during exercise were higher after KE vs placebo ingestion. Performance during a subsequent 3 kJ/kg body mass time-trial duration was not different between treatments. Study 2 reproduced the finding of an increased heart rate and ventilation after KE vs placebo ingestion, but exercise cardiac output was not different between treatments. Peak oxygen uptake (VO2peak) was not different but peak power output at VO2peak was lower after KE vs placebo ingestion. None of the cardiorespiratory effects observed after KE vs placebo ingestion were altered when the KE-associated decrease in blood pH was normalized to placebo levels through bicarbonate co-ingestion. Study 3 showed that mean power output during a 20-min time-trial was lower after ingestion of 0.35 g/kg body mass KE vs placebo in trained cyclists. The lower self-selected workload after KE ingestion was associated with a lower mean heart rate during the time-trial and a challenge to acid-base homeostasis. In summary, acute hyperketonemia elicited by KB ingestion altered selected physiological, perceptual, and performance responses during exercise in humans.