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Oral ketone ester ingestion elevates circulating dopamine concentration during ultra-endurance exercise. This is associated with improved mental alertness. Furthermore, ketone ester intake inhibits postexercise skeletal muscle macrophage infiltration, and counteracts the increase in AMPK phosphorylation after exercise, which indicates improved muscular energy status.

Available evidence indicates that elevated blood ketones are associated with improved hypoxic tolerance in rodents. From this perspective, we hypothesized that exogenous ketosis by oral intake of the ketone ester ( R)-3-hydroxybutyl ( R)-3-hydroxybutyrate (KE) may induce beneficial physiological effects during prolonged exercise in acute hypoxia. As we recently demonstrated KE to deplete blood bicarbonate, which per se may alter the physiological response to hypoxia, we evaluated the effect of KE both in the presence and absence of bicarbonate intake (BIC). Fourteen highly trained male cyclists performed a simulated cycling race (RACE) consisting of 3-h intermittent cycling (IMT180′) followed by a 15-min time-trial (TT15′) and an all-out sprint at 175% of lactate threshold (SPRINT). During RACE, fraction of inspired oxygen ([Formula: see text]) was gradually decreased from 18.6% to 14.5%. Before and during RACE, participants received either 1) 75 g of ketone ester (KE), 2) 300 mg/kg body mass bicarbonate (BIC), 3) KE + BIC, or 4) a control drink in addition to 60 g of carbohydrates/h in a randomized, crossover design. KE counteracted the hypoxia-induced drop in blood ([Formula: see text]) and muscle oxygenation by ∼3%. In contrast, BIC decreased [Formula: see text] by ∼2% without impacting muscle oxygenation. Performance during TT15′ and SPRINT were similar between all conditions. In conclusion, KE slightly elevated the degree of blood and muscle oxygenation during prolonged exercise in moderate hypoxia without impacting exercise performance. Our data warrant to further investigate the potential of exogenous ketosis to improve muscular and cerebral oxygenation status, and exercise tolerance in extreme hypoxia.

We previously demonstrated that exogenous ketosis reduces urine production during exercise, however, the underlying physiological mechanism remained unclear. Here, we, for the first time demonstrate that exogenous ketosis suppresses the exercise-induced release of atrial natriuretic peptide (ANP). However, given the limited effects of ANP on renal haemodynamics during exercise, the underlying physiological mechanism remains unknown. But downregulation of ANP might explain a new physiological mechanism by which exogenous ketosis lowers blood-free fatty acid levels.

Sports nutrition science seeks to determine optimal dietary protocols for athletes pushing the limits of human physiology in power, endurance, and skill. Traditionally, dietary interventions aimed to stimulate performance have focused on strategic intake of carbohydrates, protein, and fat. However, recent development of oral ketone supplements has increased the popularity of intermitted exogenous ketosis (IEK) as a potential nutritional strategy to stimulate training adaptation and performance in athletes. Several physiologic mechanisms are implicated in acute modulation of exercise performance by IEK. These include use of ketone bodies as an alternative substrate for oxidative ATP production in contracting muscles and ketone-mediated inhibition of glycolytic flux. The latter could lead to glycogen sparing, which may increase endurance; on the other hand, glycolytic inhibition in conjunction with ketoacidosis could be ergolytic in short maximal exercise bouts. Furthermore, preliminary evidence suggests that acute and chronic post-exercise ketosis may stimulate recovery from training. Acute IEK could stimulate muscle protein synthesis and glycogen repletion, and chronic ketone ester intake blunted overreaching symptoms during short-term endurance training overload. This protection could be attributed to improved autonomic neural balance, appetite and stress hormone regulation, and possibly attenuation of exercise-induced inflammation and oxidative stress. Such effects could conceivably either down- or upregulate training adaptation. However, research to date describing both acute and chronic exogenous ketosis in exercise and training is limited and inconclusive. Further studies are required to elucidate the specific contexts and mechanisms whereby IEK could maximally benefit athletes.