Why does dieting predict weight gain in adolescents? findings from project eat-ii: a 5-year longitudinal study.

OBJECTIVE: Dieting has been found to predict weight gain in adolescents, but reasons for this association remain unclear. This study aimed to explore potential mechanisms by which dieting predicts weight gain over time in adolescents. DESIGN: Population-based, 5-year longitudinal study. PARTICIPANTS: Adolescents (n=2,516) from diverse ethnic and socioeconomic backgrounds who completed Project EAT (Eating Among Teens) surveys in 1999 (Time 1) and 2004 (Time 2). MAIN OUTCOME MEASURE: Body mass index (BMI) change over 5 years. STATISTICAL ANALYSIS: Multiple regressions were used to examine associations between Time 1 dieting and Time 2 binge eating, breakfast consumption, fruit and vegetable intake, and physical activity. Associations were then examined between these behaviors and BMI change. Finally, to test for mediating effects, associations between dieting and BMI change were examined with and without the inclusion of these behaviors, and regression coefficients were compared. RESULTS: In female adolescents, dieting predicted increased binge eating (P<0.001) and decreased breakfast consumption (P=0.030). In male adolescents, dieting predicted increased binge eating (P<0.001), decreased physical activity (P=0.006), and a trend toward decreased breakfast consumption (P=0.064). These behaviors were also associated with increases in BMI. The association between dieting and BMI increase was weakened, but still remained significant, after binge eating, breakfast consumption, fruit/vegetable intake, and physical activity were included in the model being tested. Thus, the longitudinal association between dieting and BMI increase was partially mediated by these behaviors. CONCLUSIONS: In part, dieting may lead to weight gain via the long-term adoption of behavioral patterns that are counterproductive to weight management.