PROJECT SUMMARY Poor dietary quality and high rates of diet-related chronic diseases such as type-2 diabetes are urgent national public health priorities. Shifting dietary patterns in the United States (US) toward more environmentally sustainable ‘planetary health’ diets has the potential to improve dietary quality and prevent diet-related chronic diseases while also addressing climate change. Red meat consumption in the US is high and contributes to both diet-related chronic diseases and climate change. Fast-food restaurants are a key environment to promote ‘planetary health’-aligned food choices given the frequency of fast-food consumption, the poor dietary quality of fast foods, and their adverse health effects. Numerous restaurants and food companies have recently implemented climate-impact labels that inform consumers of each menu item’s carbon footprint (i.e., climate impact). Climate-impact menu labels are also garnering interest among policymakers. Existing research shows that nutrition labels can change behavior, but we lack evidence on whether climate labels can promote healthier as well as more climate friendly food choices. Climate labels could improve dietary quality via lower red and processed meat intake, but could also promote undeserved perceptions that unhealthy food items are healthy (i.e., a ‘health-halo’ effect). Given the rapid development and growing food industry and policy interest in climate-impact labels, there is a critical need for timely, rigorous evaluation of the real-world effects of climate labels and the optimal design to maximize behavior change. The primary objective of this application is to conduct two sequential randomized controlled trials (RCTs) to determine the degree to which climate-impact menu labels influence the healthfulness of purchases at fast-food restaurants and overall dietary intake. The first study aim is to conduct an RCT to compare the effects of different climate-impact menu label designs on the healthfulness of hypothetical fast-food meal orders in a nationally representative sample of 6,000 US adults. We will randomly assign 6,000 adults to view menus from two fast-food restaurants (one burger, one sandwich) that display one of five types of label designs: 1) control (QR code), 2) green ‘low climate impact’ label; 3) red ‘high climate impact’ label; 4) ‘climate-score’ label; and 5) traffic-light label. The second aim is to conduct an RCT to evaluate the effect of repeated exposure to climate-impact menu labels on the healthfulness of real fast-food meal orders, delivered to the participant, over an eight-week period. We will randomly assign 450 adults to one of two label conditions: control label vs. the label from Aim 1 that led to the largest improvements in the healthfulness of menu items ordered. In the third aim, we will evaluate the longitudinal effect of climate-impact menu labels on overall dietary quality (Healthy Eating Index scores) assessed via multiple 24-hour dietary recal...