PROJECT ABSTRACT Unhealthy diet and obesity are major causes of cardiovascular disease (CVD). Emerging adults (ages 18-25) are a crucial group to target with CVD prevention interventions because they have lower dietary quality and experience more rapid weight gain than adults in middle and older adulthood. Moreover, emerging adulthood is distinct developmental period during which lifelong eating behaviors and CVD risk trajectories are largely established. Communication interventions, particularly those appealing to emerging adults’ strong interest in both environmental sustainability and personal health, are a promising but understudied strategy for addressing unhealthy diet in this age group. The goal of the proposed research is to design and rigorously evaluate a communication intervention to reduce dietary risk factors for CVD among emerging adults. The first aim is to identify specific dietary substitutions that emerging adults can readily make to reduce their CVD risk and dietary environmental harms. To identify these substitutions, I will analyze dietary intake data from the National Health and Nutrition Examination Surveys linked to a comprehensive database of foods’ greenhouse gas emissions. The second aim is to develop and optimize health and environmental messages about these dietary substitutions. I will develop candidate messages, pre-test them in qualitative focus groups, then use a randomized factorial experiment with 800 emerging adults to identify the most effective message strategies. The third aim is to evaluate the impact of the messaging interventions on healthfulness of food purchases. In a longitudinal randomized controlled trial, I will assign 500 emerging adults to 1 of 4 conditions: control (no messages), health, environmental, or health + environmental messages. Participants will simulate five weekly shopping trips in an online grocery store with their assigned messages prominently displayed. I will evaluate each messaging interventions’ initial, sustained, and overall impacts on purchase healthfulness and identify the most effective type of message. This research will further NHLBI’s strategic goal of preventing CVD and NIH Nutrition Research Objective 2-6 to leverage behavioral science to initiate and sustain healthy eating. Further, this award will help me achieve my long-term career goal of becoming an independent investigator focused on effective, scalable CVD prevention interventions for emerging adults. With support from this K01, I will build on my expertise in nutrition policy to fill critical training gaps in: 1) the CVD and environmental impacts of food, 2) communication interventions for emerging adults, 3) mixed methods, and 4) advanced analytic techniques for longitudinal studies. My detailed training plan includes tutorials with my interdisciplinary mentorship team at the Harvard TH Chan School of Public Health, formal coursework, hands-on research activities, and participation in conferences, workshops, a...