Effect of acute ingestion of β-hydroxybutyrate salts on the response to graded exercise in trained cyclists

Acute ingestion of ketone salts induces nutritional ketosis by elevating -hydroxybutyrate (HB), but few studies have examined the metabolic effects of ingestion prior to exercise. Nineteen trained cyclists (12 male, 7 female) undertook graded exercise (8 min each at approximate to 30%, 40%, 50%, 60%, 70%, and 80% VO2peak) on a cycle ergometer on two occasions separated by either 7 or 14 days. Trials included ingestion of boluses of either (i) plain water (3.8mLkgbody mass(-1)) (CON) or (ii) HB salts (0.38gkgbody mass(-1)) in plain water (3.8mLkg body mass(-1)) (KET), at both 60 min and 15 min prior to exercise. During KET, plasma [HB] increased to 0.33 +/- 0.16mM prior to exercise and 0.44 +/- 0.15mM at the end of exercise (both p<.05). Plasma glucose was 0.44 +/- 0.27mM lower (p<.01) 30min after ingestion of KET and remained approximate to 0.2mM lower throughout exercise compared to CON (p<.001). Respiratory exchange ratio (RER) was higher during KET compared to CON (p<.001) and 0.03-0.04 higher from 30%VO2peak to 60%VO2peak (all p<.05). No differences in plasma lactate, rate of perceived exertion, or gross or delta efficiency were observed between trials. Gastrointestinal symptoms were reported in 13 out of 19 participants during KET. Acute ingestion of HB salts induces nutritional ketosis and alters the metabolic response to exercise in trained cyclists. Elevated RER during KET may be indicative of increased ketone body oxidation during exercise, but at the plasma HB concentrations achieved, ingestion of HB salts does not affect lactate appearance, perceived exertion, or muscular efficiency.