Summary. Obesity is associated with 13 cancers and up to 11% of cancer in the United States is associated with excess body mass index (BMI). Evidence suggests that the food environment is associated with obesity risk, which affects one third of adults. Restaurants are an important component of the food environment. One- third of Americans will eat at a fast food restaurant on a typical day. Restaurant sales have steadily increased over the past 5 decades; in 2015 restaurants spent $6.3 trillion in advertising (more than 100 times the NIH budget). Advertisements for unhealthy items are often targeted towards those at higher risk for obesity, and unhealthy food retail outlets, like fast food restaurants, are more densely located in low-income and minority communities. Therefore, the restaurant environment may more negatively impact low-income and racial minority populations. To date, research on the relationship between restaurant advertising and obesity risk has largely focused on children. Available studies are limited by cross-sectional data (limiting identification of causal relationships). To address these knowledge gaps, we will combine multiple data sources to create a unique, objective measure of local per capita restaurant advertising (adapting an approach we previously developed). This will be derived from local-level quarterly restaurant advertising spending from Kantar Media for the 100 top revenue generating restaurants in the U.S. and the annual physical addresses for all locations from each restaurant chain from AggData. We will test associations of restaurant advertising per capita with population weight gain using objectively measured BMI data for 2.3 million people (in 217 counties across 40 states and the District of Columbia, including 9 of the 10 most populous U.S. counties) from athenahealth. We will test whether this relationship is mediated by advertising exposure using data from Neilson Ad Intel. The overall objective is to leverage national data and provide a much-needed understanding of how exposure to changes in local restaurant advertising impacts adult weight gain and disparities. We propose two specific aims: 1) examine changes in chain restaurant advertising expenditures from 2012 to 2016 and test whether those changes vary by income and race/ethnicity and 2) estimate the associations between chain restaurant advertising and weight gain among U.S. adults, by race and SES and whether this relationship is mediated by the level of exposure to advertising. We will use a set of econometric techniques to assess whether these relationships are causal. We hypothesize that increases in restaurant advertising per capita were larger in areas with higher concentrations of racial/ethnic minority and low-income populations and that greater exposure to restaurant advertising will be associated with higher weight gain, particularly for low-income and racial/ethnic minority populations and those with higher advertising exposure. This research will make a highly significant contribution to our understanding of how restaurant advertising impacts weight gain and disparities among adults, with important implications for subsequent cancer outcomes and health equity.