Breath acetone change during aerobic exercise is moderated by cardiorespiratory fitness

Exhaled breath acetone (BrAce) was investigated during and after submaximal aerobic exercise as a volatile biomarker for metabolic responsiveness in high and lower-fit individuals in a prospective cohort pilot-study. Twenty healthy adults (19-39 years) with different levels of cardiorespiratory fitness (VO2peak), determined by spiroergometry, were recruited. BrAce was repeatedly measured by proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) during 40-55 min submaximal cycling exercise and a post-exercise period of 180 min. Activity of ketone and fat metabolism during and after exercise were assessed by indirect calorimetric calculation of fat oxidation rate and by measurement of venous beta-hydroxybutyrate (beta HB). Maximum BrAce ratios were significantly higher during exercise in the high-fit individuals compared to the lower-fit group (t-test; p= 0.03). Multivariate regression showed 0.4% (95%-CI = -0.2%-0.9%, p= 0.155) higher BrAce change during exercise for every ml kg(-1) min(-1) higher VO2peak. Differences of BrAce ratios during exercise were similar to fat oxidation rate changes, but without association to respiratory minute volume. Furthermore, the high-fit group showed higher maximum BrAce increase rates (46% h(-1)) in the late post-exercise phase compared to the lower-fit group (29% h(-1)). As a result, high-fit young, healthy individuals have a higher increase in BrAce concentrations related to submaximal exercise than lower-fit subjects, indicating a stronger exercise-related activation of fat metabolism.