Socioeconomic, behavioral, and psychological correlates of body weight and weight gain: evidence from a 12-year German panel study

Background Overweight and obesity are major public health challenges in Germany. Body weight is shaped by a wide range of socioeconomic, behavioral, and psychological factors, but less is known about how these factors jointly relate to weight gain among adults in Germany. Methods Data were drawn from the adult cohort of the National Educational Panel Study (NEPS-SC6). The analytical sample included 8,209 individuals aged 28–55 years at baseline (2011/12), followed over approximately 12 years. In this exploratory study, cross-sectional associations with BMI and overweight/obesity status were estimated using regression models, while longitudinal associations with BMI changes were analyzed using fixed-effects panel models, capturing within-individual changes. Missing values were handled by multiple imputation (50 imputed datasets). Results Higher household income (-0.16), tertiary education (-0.41), higher social origin (-0.26), greater conscientiousness (-0.64), higher neuroticism (-0.27), and more frequent sports participation (-0.38) were associated with lower BMI at baseline, whereas higher extraversion was associated with higher BMI (+ 0.23). Women had significantly lower BMI than men (-1.42). Longitudinal analyses showed that BMI increased over time (0.08 points per year), with the steepest increase in the first three years. Within individuals, increases in household income (+ 0.10) and transitions into cohabitation with a partner (+ 0.29) were associated with higher BMI, whereas smoking (-0.52) and greater sports participation (-0.13) were associated with lower BMI; the smoking association likely reflects, at least partly, weight gain after cessation (smoking prevalence fell from 30% to 20%). Women experienced a stronger BMI increase than men only at the last measurement point (2023/24), and those with tertiary education (-0.02) showed slower BMI increases. Conclusions Body weight and weight gain are associated with socioeconomic, behavioral, and psychological factors. Among the Big Five personality traits, conscientiousness showed the strongest association with lower BMI, whereas neuroticism was unexpectedly associated with lower rather than higher BMI and warrants replication with more comprehensive personality measures. Higher educational attainment and more frequent physical activity were associated with lower BMI and, within individuals, with more favorable weight trajectories; given the exploratory design, these associations should not be interpreted causally. The findings highlight the relevance of psychological characteristics for obesity research and prevention.