Ketone monoester reduces blood glucose, exogenous CHO oxidation and oxidation efficiency in trained male cyclists when fed 120 g/h of CHO during exercise

We examined the effects of ketone monoester (KME) and carbohydrate (CHO) co-ingestion on exogenous CHO oxidation (via U- 13 C enriched glucose-fructose drinks), metabolomic responses and exercise capacity. In a randomised crossover design (after 36 h of CHO loading and pre-exercise meal of 12 and 2 g.kg -1 , respectively), eight trained male cyclists (V̇O 2max ; 66 ± 7 mL.kg -1 .min -1 ) ingested 0 g.h -1 (PLA), 120 g.h -1 CHO (CHO), or 120 g.h -1 CHO + 75 g ketone monoester (CHO + KME) during 3 h of cycling at power outputs corresponding to 95 % of lactate threshold (LT) followed by exercise to exhaustion at 150 % LT . Mean blood glucose concentrations during exercise were different between all pairwise comparisons (P<0.05) such that CHO > CHO + KME > PLA (4.9 ± 0.3, 4.4 ± 0.2, 3.7 ± 0.4 mmol.L -1 , respectively). Mean exogenous CHO oxidation (1.35 ± 0.15 vs 1.50 ± 0.16 g.min -1 , P<0.01) and oxidation efficiency was lower in CHO + KME (67 ± 7 %) compared to CHO (75 ± 6%, P <0.01). Exercise capacity was greater (P<0.05) in CHO (349 ± 189 s) and CHO + KME (319 ± 225 s) compared to PLA (75 ± 105 s), though no differences were evident between CHO and CHO+KME (P>0.05). Ketone monoester ingestion increased abundance of metabolites associated with carbohydrate metabolism (Glucaric acid) and protein turnover (3-Methylhistidine). We conclude that ketone monoester ingestion does not enhance exercise capacity and reduces blood glucose concentrations, exogenous CHO oxidation and oxidation efficiency when compared to CHO alone.