Pathways linking socioeconomic status to obesity through depression and lifestyle factors among young US adults

Obesity and depression are two diseases of major public health importance. While both correlate with each other, potential pathways involving depression that would link socioeconomic status (SES) to lifestyle factors and obesity have not been systematically examined using nationally representative data. Using rich data on 2217 US young adults aged 20–39 years from the 1999–2004 National Health and Nutrition Surveys (NHANES) and multivariate linear and logistic regression models, we examined associations between major depressive disorder (MDD), dietary intake, physical activity (PA), and measured body mass index (BMI) controlling for socio-demographic factors. Further, structural equation models (SEM) were fit to test pathway explaining SES disparities in BMI through MDD and lifestyle factors. Recent prevalence of MDD was lower among young US men than women (6.4% vs. 9.2%) although their prevalence of obesity was similar (21.2% vs. 22.7%). Among women, MDD was associated with higher BMI and inversely associated with PA, but not among men. MDD was specifically associated with increased risk of morbid obesity (BMI ≥ 40) among women (OR: 2.88 (1.32, 6.30)). Using SEM, a main pathway linking SES to BMI among women was linking SES → food insecurity → MDD → PA → BMI. A main pathway linking MDD to BMI in both genders was going through PA rather than overall dietary quality. Gender and ethnic differences existed underlying how MDD, SES and lifestyle factors were associated with adiposity. Future prospective studies are needed to examine potential mechanisms using physiological markers of depression, lifestyle and obesity.