Does co-morbid depression alter the inverse relationship between obesity and substance use disorders?

BACKGROUND Substance use disorders and obesity are often inversely related to one another, hypothetically due to competition over shared neurobiological reward circuitry. However, obesity and substance use disorders share common risk factors, such as other psychiatric disorders. It is unknown whether the inverse relationship between obesity and substance use disorders continues to exist in the presence of shared risk factors. METHODS For the current study, we examined the associations between major depression, alcohol and drug use disorders, and overweight/obesity status in a nationally representative sample of U.S. adults (n=40,715). RESULTS Our findings demonstrated that adults with major depression were more likely to be obese, whereas adults with alcohol or drug use disorders were less likely to be obese. However, the inverse relationship between substance use and obesity continued to exist in adults with co-morbid depression. Adults with depression disorders co-morbid with alcohol (Relative Risk [RR]=0.63, 95% CI=0.47-0.84) or drug (RR=0.54, 95% CI=0.36-0.81) use disorders were less likely to be obese vs normal weight. CONCLUSIONS Our findings provide support for the proposal that excess food consumption and excess drug use appear to compete over shared neurobiology even when the motivation to self-medicate with either food or substances might be elevated.