The Association Between BMI and Depression Symptoms Among College Students: A Study Based on Random Intercept Cross-Lagged Model

Objective: To explore the longitudinal association between BMI and depressive symptoms among college students and to explore whether this association differs by gender. Method: A quantitative longitudinal design was adopted, and 1336 college students were tracked for a period of three years. The SCL-90 and BMI calculated from objectively measured height and weight were used to assess depressive symptoms and body mass status among college students. Using random intercept cross-lagged model analysis, we analyzed the temporal lagged associations between BMI and depressive symptoms and constructed stratified models for different genders to examine differences in these associations. Result: The results showed that there was a negative bidirectional predictive effect between BMI and depressive symptoms. Within-person deviations in depressive symptoms at T1 were significantly and negatively associated with deviations in BMI at T2 (β = −0.126, p = 0.003). The path from T2 to T3 was also significant (β = −0.079, p = 0.004). The BMI fluctuation at T1 could significantly negatively predict the depressive symptoms fluctuation at T2 (β = −0.133, p = 0.004). The path from T2 to T3 was also significant (β = −0.149, p = 0.003). At the interpersonal level, there was a significant positive correlation between RI_X and RI_Y (β = 0.142, p = 0.012). This means that, at the individual difference level, individuals with higher stable BMI traits also tend to have higher stable depressive symptoms traits. At the intra-individual level, the correlation between the BMI fluctuation and the depressive symptoms fluctuation at the same time point was not significant. Gender differences suggested that the longitudinal association between BMI and depressive symptoms may differ by gender. The BMI–depressive symptoms dynamics among male students appeared more complex. Conclusions: In the college student population, the association between BMI and depressive symptoms mainly reflects stable individual differences rather than continuous intra-individual dynamic effects. These findings highlight the value of separating between-person differences from within-person change when studying the physical and mental health of college students.