Effects of the time of day (morning vs. afternoon) of exercise program on body composition: a systematic review and meta-analysis of randomized clinical trials

In general, exercise at any time of the day improves body composition. However, it is not yet clear which time of day is optimal for exercise. Therefore, the effects of exercise program timing (morning vs. afternoon) on body composition have been evaluated. Systematic reviews and a meta-analysis were conducted on randomized clinical trials (published up to July 2026) examining differences in body composition among individuals aged 18 years or older who exercise in the morning (AM) or evening (PM). Retrieved data were pooled when computing weighted mean differences (WMDs) between three groups (AM, PM, and control) for weight, BMI, fat mass, fat percent, and lean tissue. The present study showed that both morning and evening exercise reduced weight, BMI, and fat mass compared with the control group. In addition, our study showed that PM training reduced weight (standardized mean difference (SMD):-0.77 kg; 95% CI: -1.05 to -0.50; P < 0.001), lean tissue (SMD: -0.20 Kg; 95% CI: -0.33 to -0.06; P < 0.001), fat mass(SMD: -0.58 kg; 95% CI: -0.81 to -0.35; P < 0.001), and fat percent (WMD: -0.35%; 95% CI: -0.65 to -0.05; P = 0.02) compared to AM training. The evening exercise showed modestly larger reductions than the morning exercise in pooled analyses, but high heterogeneity, reliance on BIA, and inconsistent nutritional control preclude firm recommendations. Larger, standardized trials with DXA and biomarker confirmation are needed.