Time of Day of Aerobic Exercise Training Alters the Metabolome in Adults with Overweight or Obesity: A Secondary Analysis

Objective: The goal of this exploratory secondary analysis was to examine how time of day of aerobic exercise training alters fasting plasma metabolites in adults with overweight or obesity. Methods: Adults with overweight or obesity (n = 33, age 28–49, BMI: 25–40 kg/m2) were randomly assigned to AM (6:00–10:00) or PM (15:00–19:00) supervised aerobic exercise training for 15 weeks. Untargeted plasma metabolomics were performed in a subset of n = 28 participants who completed the intervention and provided fasted blood collections. This study is registered at clinicaltrials.gov (NCT04262115) as of 2/10/2020. Results: Following 15 weeks of aerobic exercise training, AM exhibited increased catecholamines (p < 0.05). This change in catecholamines was correlated with changes in HbA1C (r = −0.61, p = 0.01), such that larger increases in catecholamines were associated with larger decreases in HbA1C. Following 15 weeks of exercise training, PM exhibited increased serotonin (p = 0.04) and decreased L-tryptophanamide (p = 0.01), indole-3-acetate (p < 0.001), and indole-3-acetic acid (p < 0.001). Larger increases in plasma serotonin were correlated with larger increases in VO2 max (mL/kg/min) (r = 0.73, p = 0.01). Conclusions: In conclusion, time of day of aerobic exercise differentially impacted plasma metabolomic profiles, which were correlated with cardiometabolic health indicators. This study provides preliminary evidence that the timing of exercise may differentially impact physiological systems, which may, in turn, lead to differential effects on clinical health parameters.