PROJECT SUMMARY Family-based lifestyle intervention (FBLI) is the gold standard for treating adolescent obesity, which emphasizes the importance of making family-wide changes to the shared home environment. Yet, program assessments overwhelmingly focus on the individual adolescent. Understanding the impact of FBLIs beyond the identified adolescent is important, given that obesity is a familial disease and there are likely bidirectional relations between an adolescent’s treatment success and broader changes in their household. It is unknown if family-wide changes are made within FBLI, or if non-targeted family members experience weight-related benefits. These data are critical, given that weight losses observed in adolescent obesity treatments are generally modest, with no clear guidance regarding the optimal family-based treatment approach during this distinct developmental period. Towards that end, we propose to leverage our ongoing randomized clinical trial (RCT) of TEENS+, a FBLI for adolescents with obesity, to determine: 1) if family-wide changes to the shared home environment are implemented, 2) if ripple effects to untreated family members are observed, and 3) whether these changes are predictive of adolescents’ weight management success. Via R01HD095910, we are evaluating two approaches to involving parents in FBLI to treat adolescent obesity. In this RCT, all adolescents participate in TEENS+, our 4m behavioral weight loss (BWL) treatment. Parents are randomized to either 1) parent skills training based on authoritative parenting (Parents as Coaches; PAC) or 2) concurrent parent BWL (Parent Weight Loss; PWL). TEENS+ was informed by our pilot (HD084930), which included 82 adolescent (M age=13.7±1.2yrs; 52% Black)/parent dyads. We demonstrated that both parent treatments yielded adolescent weight loss at the end of the 4m treatment. Further, improvements to the obesogenic home food environment were observed in both groups; yet a more comprehensive assessment of the shared home environment is needed to determine if broader family-wide changes, including weight changes of non-targeted family members, are executed, and if these changes predict adolescent weight loss. To that end, adolescent/parent dyads will be randomized to TEENS+PAC or TEENS+PWL via our ongoing R01 trial. This ancillary R21 will expand trial assessments and conduct a comprehensive assessment of the shared home feeding and weight environment of the target adolescents. Specifically, we will enroll non-targeted children (8- 17yrs) and caregivers living in the same household as the target parent/adolescent dyad (N=60 families; 30 per treatment group). At 0, 2, 4 (primary endpoint), and 8m, the target parent/adolescent dyad and non- targeted children (n=~80) and caregivers (n=~60), will complete anthropometric assessments. Measures of the shared home feeding and weight environment will also be conducted. Results will determine the familial reach of TEENS+ and reveal potential me...