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 (V̇O₂ peak), resting metabolic rate, and blood markers were assessed at baseline and 12 weeks. Body composition and V̇O₂ 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). V̇O₂ 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.