Effect of Acute Ketone Monoester Ingestion on Cardiorespiratory Responses to Exercise and the Influence of Blood Acidosis

Abstract

ABSTRACT Ketone monoester (KE) ingestion can induce hyperketonemia and blood acidosis. We previously found that acute ingestion of 0.6 g·kg−1 body mass KE increased exercise heart rate (HR) compared with placebo. Purpose This study aimed to examine the effect of KE ingestion on exercise cardiac output (Q˙) and the influence of blood acidosis. We hypothesized that KE versus placebo ingestion would increase Q˙, and coingestion of the pH buffer bicarbonate would mitigate this effect. Methods In a randomized, double-blind, crossover manner, 15 endurance-trained adults (peak oxygen uptake (V̇O2peak), 60 ± 9 mL·kg−1·min−1) ingested either 0.2 g·kg−1 sodium bicarbonate or a salt placebo 60 min before exercise, and 0.6 g·kg−1 KE or a ketone-free placebo 30 min before exercise. Supplementation yielded three experimental conditions: basal ketone bodies and neutral pH (CON), hyperketonemia and blood acidosis (KE), and hyperketonemia and neutral pH (KE + BIC). Exercise involved 30 min of cycling at ventilatory threshold intensity, followed by determinations of V̇O2peak and peak Q˙. Results Blood [β-hydroxybutyrate], a ketone body, was higher in KE (3.5 ± 0.1 mM) and KE + BIC (4.4 ± 0.2) versus CON (0.1 ± 0.0, P < 0.0001). Blood pH was lower in KE versus CON (7.30 ± 0.01 vs 7.34 ± 0.01, P < 0.001) and KE + BIC (7.35 ± 0.01, P < 0.001). Q˙ during submaximal exercise was not different between conditions (CON: 18.2 ± 3.6, KE: 17.7 ± 3.7, KE + BIC: 18.1 ± 3.5 L·min−1; P = 0.4). HR was higher in KE (153 ± 9 bpm) and KE + BIC (154 ± 9) versus CON (150 ± 9, P < 0.02). V̇O2peak (P = 0.2) and peak Q˙ (P = 0.3) were not different between conditions, but peak workload was lower in KE (359 ± 61 W) and KE + BIC (363 ± 63) versus CON (375 ± 64, P < 0.02). Conclusions KE ingestion did not increase Q˙ during submaximal exercise despite a modest elevation of HR. This response occurred independent of blood acidosis and was associated with a lower workload at V̇O2peak.