Acute and Intermittent Exogenous Ketosis to Support Recovery From Exercise and Adaptations to Exercise Training: A Narrative Review

The ketone bodies acetoacetate (AcAc) and β-hydroxybutyrate (βHB) have pleiotropic effects in multiple organs including the brain, heart, and skeletal muscle by serving as an alternative substrate for energy provision, and by acting as a signaling molecule modulating inflammation, oxidative stress, anabolic and catabolic processes, and gene expression. Ketogenic precursors such as 1,3-butanediol and medium-chain fatty acids, and ketone body-containing compounds such as ketone salts and ketone esters are commercially available and collectively termed exogenous ketone supplements (EKS). Ingestion of EKS produces an acute transient (1-2 h) increase in circulating AcAc and βHB concentrations, which has been termed "acute nutritional ketosis" or "intermittent exogenous ketosis". Many studies have failed to observe benefits of acute ingestion of EKS on various tests of exercise capacity and performance, but recent studies, albeit small in number, have suggested beneficial effects of EKS on recovery, sleep, overreaching, and adaptation to exercise training. This review describes the rationale and potential mechanistic basis for the proposed effects of EKS on these outcomes, as well as critically appraising the existing literature in this field, which at present is largely exploratory and requires more human studies with ecologically valid designs to address important knowledge gaps.