PROJECT SUMMARY The UAB NORC contributed to the creation of the International Weight Control Registry (IWCR), an online prospective cohort to study why obesity rates differ in different populations and to identify factors that may contribute long-term success in weight management. This competitive revision will allow us to rapidly increase participation in the IWCR to capture and analyze data on behavioral, environmental, cultural, socio-economic, motivational, and social factors that explain why some groups (e.g. some minorities, those in Southeastern US) have higher rates of obesity than others and why some groups may need different strategies for long-term success. There are currently 5 major research centers who will initiate enrollment in the IWCR in June 2020. With this revision, we expect to reach a minimum of 1000 participants by Jan 2021 and an additional 1000 – 2000 by the end of the 1-year study period. Data analysis during the first year will focus on understanding why rates of obesity differ between different geographical regions of the US with as especial emphasis on why rates are so high in the Southeastern U.S. Over the long-term the IWCR will be a valuable resource for UAB NORC researchers and for the global obesity research community. This revision has three specific aims. Specific aim #1. Accelerate establishment of the IWCR as a unique resource to help UAB NORC researchers in their efforts to reduce the burden of obesity. We expect to enroll at least 2000 US individuals into the IWCR within by Jan 2021 and these participants will complete the online questionnaires. In a subset of 200 participants, we will collect additional in-depth measures to use to validate questionnaires for registry expansion. Specific aim #2. Examine geographical differences in obesity rates and weight loss success in the US. To achieve this aim, we will use nationally representative cross-sectional data from the 2004-2018 National Health Interview Study and longitudinal 1-year data from the IWCR. We hypothesize that predictive modeling techniques will identify novel clusters of factors predisposing individuals in the South to poorer weight loss outcomes during the 1-year study period. Specific aim #3. Demonstrate the value of the IWCR as a tool to facilitate collaboration between NORCs and between obesity researchers. We will take advantage of the rich talent of researchers at the 5 institutions currently supporting the IWCR to solicit proposals for research that can be conducted using IWCR data and which can be completed in 1 year. The PIs of the 5 centers will review and prioritize these proposals and data analysis capacity from UAB and USMA will be allocated to the strongest proposals. We expect that in this one-year competitive revision, we can both acquire important information about why rates of obesity differ geographically as well as establishing the IWCR as a valuable resource for UAB researchers and for the entire obesity research community.