Wellness Achieved Through Changing Habits (WATCH): An Acceptance-Based Healthy Lifestyle Intervention for Diverse Adolescents - ABSTRACT Overweight/obesity (OW/OB) affects 14 million adolescents in the United States, disproportionately affecting girls and racial/ethnic minorities, increasing their risk of cardiovascular disease and type 2 diabetes. Behavioral weight loss interventions are the foundation of obesity treatment modalities, yet many have led to limited weight loss and weight regain is common. Limited success in adolescent weight loss interventions may be attributed primarily to adolescents’ lack of self-regulation skills, which are essential for adhering to diet and physical activity goals. There is a critical need for development of interventions that teach self-regulation skills to adolescents in order to adapt to pervasive biological and environmental cues that are often experienced during weight loss. An innovative behavioral treatment, acceptance-based therapy (ABT), focuses on self- regulation skills and increasing mindfulness and tolerance of negative or uncomfortable emotions. ABT has demonstrated strong evidence as an effective weight loss strategy in adults. Our group utilized an adolescent- engaged approach to develop, implement, and test the feasibility and acceptability of an ABT weight loss intervention for adolescent girls with OW/OB. The feasibility study was a 6-month ABT behavioral weight loss intervention comprised of 15 in-person group sessions (90-minutes each) over a 6-month period led by an instructor trained in ABT. The feasibility study demonstrated strong acceptability among adolescent girls with OW/OB. The objective of this study, called the Wellness Achieved Through Changing Habits (WATCH) trial, is to test the efficacy of an ABT intervention versus an enhanced care (EC) intervention on markers of cardiometabolic health, health related behaviors, and psychological factors. During the R61 phase (year one), we will finalize all WATCH policies and procedures including clinical trials registration, manual of operations, IRB approvals, convening the DSMB board, and begin recruitment. We will also submit a NIH progress report on participant recruitment, demographics, and intervention fidelity. During the R33 phase (years 2-5), we propose a randomized controlled trial of 148 adolescent girls (≥40% racial/ethnic minorities) with OW/OB to test the hypothesis that those randomized to ABT (vs. EC) will have significantly decreased BMI z-score (primary outcome) and body fat, and improved blood pressure and blood lipids at post-treatment, 6-month follow-up, and 12-month follow-up. We also hypothesize that relative to EC intervention, ABT will significantly improve health-related behaviors and psychological factors. As an exploratory aim, we will examine the extent to which ABT’s effects on weight and body composition are mediated by improvements in behavioral and psychological factors, and identify key moderators of ABT intervention effects including baseline demographic and psychological factors. This study will yield a novel, obesity intervention tailored to the needs of adolescents with OW/OB by developing self-regulation skills and providing tools to promote cardiometabolic health.