AUTHOR=Dearlove David J. , Holdsworth David , Kirk Tom , Hodson Leanne , Charidemou Evelina , Kvalheim Eline , Stubbs Brianna , Beevers Andrew , Griffin Julian L. , Evans Rhys , Robertson Jeremy , Clarke Kieran , Cox Pete J. 

TITLE=β-Hydroxybutyrate Oxidation in Exercise Is Impaired by Low-Carbohydrate and High-Fat Availability

JOURNAL=Frontiers in Medicine

VOLUME=Volume 8 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2021.721673

DOI=10.3389/fmed.2021.721673

ISSN=2296-858X

ABSTRACT=Abstract
Purpose: Here, we determined ketone oxidation rates in athletes under metabolic conditions of high and low carbohydrate and fat availability.
Methods: Six healthy male athletes completed 1 hour of bicycle ergometer exercise at 75% maximal power on three occasions. Prior to exercise, participants consumed 573 mg·kg bw-1 of a ketone ester containing a 13C label. To manipulate carbohydrate availability, 36 hours before each visit athletes undertook glycogen depleting exercise followed by isocaloric high-carbohydrate or very-low-carbohydrate diets. To manipulate fat availability, participants were given a continuous infusion of lipid during two visits. Using stable isotope methodology 𝛽-hydroxybutyrate oxidation rates were therefore investigated under the following metabolic conditions: (i) high carbohydrate + normal fat (KE+CHO); (ii) high carbohydrate + high fat (KE+CHO+FAT); and (iii) low carbohydrate + high fat (KE+FAT).
Results: Pre-exercise intramuscular glycogen was approximately halved in the KE+FAT vs. KE+CHO and KE+CHO+FAT conditions (both p<0.05). Blood free fatty acids and intramuscular long-chain acylcarnitines were significantly greater in the KE+FAT vs. other conditions and in the KE+CHO+FAT vs. KE+CHO conditions before exercise. Following ingestion of the 13C labelled ketone ester, blood 𝛽-hydroxybutyrate levels increased to ≈4.5 mM before exercise in all conditions. 𝛽-hydroxybutyrate oxidation was modestly greater in the KE+CHO vs. KE+FAT conditions (mean diff. = 0.09 g·min-1; p=0.03; d=0.3), tended to be greater in the KE+CHO+FAT vs. KE+FAT conditions (mean diff. = 0.07 g·min-1; p=0.1; d=0.3) and were the same in the KE+CHO+FAT vs. KE+FAT conditions (p<0.05; d<0.1). A moderate positive correlation between pre-exercise intramuscular glycogen and 𝛽-hydroxybutyrate oxidation rates during exercise was present (p=0.04; r=0.5). Post-exercise intramuscular 𝛽-hydroxybutyrate abundance was elevated in the vs. KE+CHO and KE+CHO+FAT conditions (both, p<0.001; d=2.3).
Conclusion: 𝛽-hydroxybutyrate oxidation rates during exercise are modestly impaired by low carbohydrate availability, independent of circulating 𝛽-hydroxybutyrate levels.