Abstract: The etiology of obesity is complex and is driven by different factors in different populations, including across developmental stages, in different racial and ethnic communities, and at different levels of socioeconomic status (SES). It is important to identify the factors that promote excess energy intake in the highest risk populations to develop evidence-based, effective obesity prevention and treatment strategies. Over the past decade, it has become apparent that studying behavioral phenotypes that predict overweight, obesity, and weight change across the lifespan is critical for developing individualized intervention strategies with a high degree of efficacy and effectiveness. One novel phenotype that has been identified and characterized is sensitization of the relative reinforcing value (RRV) of food. This is defined as an increase in the RRV of a food after repeated, daily consumption of high energy density (HED) food for two weeks. In adults, sensitization is positively associated with BMI and prospectively predicts weight gain over time. The cross-sectional relationship between zBMI and sensitization has been replicated in a cohort of adolescents enrolled in the UBSNAK study and recent data have shown that, as in adults, sensitization prospectively predicts zBMI change in adolescents. It is also known, from preliminary work, that the relationship between food insecurity and zBMI is associated with other individual, behavioral, and environmental factors, such as delay discounting, perceived stress, and self-efficacy for healthy eating. The goals of the proposed study are 1) to investigate the relationship between food insecurity and sensitization 2) to determine the role of sensitization in determining zBMI and zBMI change in a population of moderate to low-income adolescents and 3) to determine how adolescent food insecurity interacts with household food insecurity to moderate the relationship between sensitization and zBMI change. The first aim will test the hypothesis that food insecurity is related to sensitization and that this relationship is mediated by individual, behavioral, and environmental factors. The second aim will test the hypothesis that household food insecurity moderates the relationship between sensitization and zBMI change over time in adolescents. The third aim will test the hypothesis that adolescent food insecurity interacts with household food insecurity to moderate the relationship between sensitization and zBMI change and that one factor that impacts this relationship is adolescent eating autonomy. When taken together, this study will help to identify and characterize novel intervention targets in a population of adolescents at higher risk for overweight and obesity.