ObjectiveThe study aims to explore the relationship between modifiable lifestyle factors (physical activity, sedentary time, body composition, muscle strength) and mental health, and predict future changes in mental health.MethodsA cross-sectional survey was conducted on 133 men (age: 29.03 ± 6.605 years, BMI: 23.58 ± 2.688 kg/m²) to assess baseline body composition, muscle strength, sedentary time, and mental health, with follow-up at 3 months. F-tests were employed to compare the differences in mental health on sedentary time and body composition variables. Spearman correlation analysis was used to examine correlations between variables.ResultsSpearman’s correlation analysis showed that sedentary time, muscle strength and mental health of the subjects were significantly correlated. BMI, BFM, BFMI, PBF were higher in subjects with ≥ 4 h of sedentary time than in the other two shorter sedentary time groups. Subjects with higher PBF (p = 0.047, η2 = 0.030) and BFM (p = 0.032, η2 = 0.035) had severer depression. Subjects who sat for ≥ 4 h at a time were more severely depressed than those who sat for 2–4 h (p = 0.020). Change in depression was significantly negatively correlated with BMI, BFM, BFMI and PBF. Subjects with higher PBF (p = 0.023, η2 = 0.050) and BFM (p = 0.005, η2 = 0.075) at the baseline had less change in depression.ConclusionA Significant correlation was found between sedentary time, body composition and mental health, and baseline body composition predicted changes in mood three months later.