Acute effects of β-hydroxybutyrate on left ventricular function in young, healthy adults

Interest in ketones as a cardiac "super fuel" has grown significantly following reports of a marked increase in cardiac output after exogenous ketone administration in heart failure. However, the extent to which this increase in cardiac output is related to changes in cardiac contractility, and dependent on the presence of heart failure, remains incompletely understood. Therefore, we performed a randomized, double-blind, placebo-controlled study of oral ketone ester in young healthy volunteers. Baseline cardiac magnetic resonance imaging was performed and repeated every 15 min for 60 min after ketone and placebo ingestion to assess changes in left ventricular function. As expected, circulating β-hydroxybutyrate increased rapidly after ketone ingestion, but did not change with placebo (interaction: P < 0.001). Consistent with prior investigations, ketone ingestion resulted in an average 1 L/min increase in cardiac output after 60 min that did not occur with placebo (interaction: P = 0.026). This increase in cardiac output was primarily driven by an increase in heart rate after ketone ingestion (interaction: P = 0.018), with only a modest increase in stroke volume (interaction: P = 0.037). Changes in left ventricular strain and twist mechanics were limited. Taken together, the increase in cardiac output following an acute elevation in circulating β-hydroxybutyrate is primarily driven by changes in cardiac chronotropy, with minimal inotropic contribution.NEW & NOTEWORTHY In this randomized, double-blind, placebo-controlled study of oral ketone ester in young healthy volunteers, we show a marked increase in cardiac output (∼1 L/min), driven primarily by changes in chronotropy. The cardiac magnetic resonance imaging data support the limited role for inotropy.