Indirect Effects of a Cognitive-Behavioral Intervention on Adolescent Weight and Insulin Resistance Through Decreasing Depression in a Randomized Controlled Trial

Objective Depression is linked to excess weight, insulin resistance, and type 2 diabetes (T2D). We previously reported that in adolescent girls at-risk for T2D with moderately elevated depression, randomization to cognitive-behavioral therapy (CBT) produced greater decreases in depression at post-treament and greater decreases in fasting/2-h insulin at 1 year, compared to health education (HE). The current study is a secondary analysis of this parallel-group randomized controlled trial. We examined whether decreasing depression explained intervention effects on body composition and insulin outcomes. We hypothesized that decreases in depression would be an explanatory mediator and that indirect effects would be strongest at higher levels of baseline depression. Methods Participants were 12–17 years girls with overweight/obesity and family history of T2D randomized to 6-week group CBT (n = 58) or HE (n = 61). Procedures took place at an outpatient pediatric clinic. At baseline, post-treatment, and 1 year, adolescents completed the Center for Epidemiologic Studies-Depression Scale to assess depression symptoms; body mass index (BMI [kg/m2]) was measured from height/fasting weight; insulin resistance was derived from 2-h oral glucose testing. Adiposity was assessed with dual-energy X-ray absorptiometry at baseline and 1 year. Indirect effects of intervention were tested on 1-year changes in BMI, adiposity, and insulin through decreases in depression. Baseline depression was tested as a moderator of mediation. Results There was an indirect effect of CBT on decreased 1-year fasting insulin via decreases in depression during treatment, among adolescents with more elevated baseline depression. Conclusions Decreasing elevated depression may be one mechanism in the targeted prevention of T2D in at-risk adolescents.