PROJECT SUMMARY/ABSTRACT Comprehensive behavioral treatments are effective at promoting weight loss and improving clinical outcomes among adults with obesity. However, a large majority of individuals with obesity never take the first step of initiating these treatments (even when barriers to cost and access are reduced), severely limiting the population impact of evidence-based weight management treatments. To address this challenge and take advantage of growing access to comprehensive weight loss treatments, our team has developed a tool designed to increase initiation of evidence-based behavioral weight loss treatments among eligible but non- treatment seeking adults (“mobilization tool”). As part of this tool, patients answer brief questions and receive automated, individually tailored feedback. This feedback targets empirically and theoretically relevant constructs for treatment initiation using a Motivational Interviewing approach that supports patient autonomy. The tool is completed by patients in the days prior to a scheduled primary care appointment and contains explicit endorsement by patients’ primary care provider (PCPs), taking advantage of PCPs’ influence while not relying on PCPs to initiate weight counseling. It is also designed to be low burden and high acceptability to PCPs to facilitate dissemination, if effective. We previously conducted a cluster randomized feasibility pilot trial to inform plans for a fully powered test of the effectiveness of the mobilization tool. The pilot showed that the tool was highly usable, informative, and enjoyable; feasibility goals were met; and a signal of an effect was observed. We are now prepared to conduct an adequately powered cluster randomized clinical trial to compare the effects of the mobilization tool and a static treatment description (comparator tool), and to examine how effects differ across key demographic factors. We will recruit and randomize PCPs (n=36) and patients with obesity (n=828) who have an upcoming appointment with enrolled PCPs. All enrolled patients will complete either the mobilization tool or the comparator tool, depending on their randomization arm, and will be informed that they have free access to comprehensive weight loss treatment. We will compare the two study arms on the proportion who initiate weight loss treatment (primary outcome), session attendance, and weight loss outcomes at 6 months (secondary outcomes). Because weight loss programs historically have had lower uptake by individuals who are men, Black/African American, younger, have lower income, and have lower educational attainment, we will recruit a diverse population to allow for comparisons of effects across gender, race, age, income, and education. If effective, the proposed mobilization tool could be disseminated within primary care practices to increase the number of adults with obesity who initiate evidence-based weight loss treatment, resulting in greater population weight loss and meaningful...