The efficacy of morning versus evening exercise for weight loss: A randomized controlled trial

OBJECTIVE: The aim of this study was to investigate the influence of morning versus evening exercise on weight loss, cardiometabolic health, and components of energy balance. METHODS: A total of 100 inactive adults with overweight or obesity were randomized to morning exercise (AMEx; 06:00–09:00), evening exercise (PMEx; 16:00–19:00), or wait‐list control (CON). AMEx and PMEx were prescribed 250 min·wk(−1) of self‐paced aerobic exercise for 12 weeks. Anthropometry and body composition, physical activity, and dietary intake were assessed at baseline, 6 weeks, and 12 weeks. Cardiorespiratory fitness (V̇O(2)peak), resting metabolic rate, and blood markers were assessed at baseline and 12 weeks. Body composition and V̇O(2)peak were also measured at 3‐ and 6‐month follow‐up. RESULTS: AMEx and PMEx lost weight during the intervention (mean [SD], AMEx, −2.7 [2.5] kg, p < 0.001; PMEx, −3.1 [3.4] kg, p < 0.001). V̇O(2)peak significantly increased in both intervention groups, and these changes were different from CON (AMEx, +4.7 mL·kg(−1)·min(−1), p = 0.034; PMEx, +4.2 mL·kg(−1)·min(−1), p = 0.045). There were no between‐group differences for resting metabolic rate or physical activity. At 12 weeks, total energy intake was significantly reduced in both AMEx and PMEx versus CON (AMEx, −3974 kJ, p < 0.001; PMEx, −3165 kJ, p = 0.001). CONCLUSIONS: Adults with overweight and obesity experience modest weight loss in response to an exercise program, but there does not appear to be an optimal time to exercise.