Exogenous ketosis increases circulating dopamine concentration and maintains mental alertness in ultra-endurance exercise

Eighteen recreational runners took part in a 100 km trail run or ran to premature exhaustion (80 km: 6 runners; 60 km: 4 runners), receiving either the ketone ester (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (n = 9) or a noncaloric placebo (n = 9) before, during and after the run. Blood d-beta-hydroxybutyrate was about 2 to 3 mM with ketone ester versus under 0.3 mM with placebo. In the placebo group the run increased visual reaction times from 353 to 419 ms and movement execution times from 174 to 245 ms, an effect fully negated by ketone ester (P < 0.05).