Meat consumption is a major driver of climate change. Interventions that reduce meat consumption may improve public health and promote environmental sustainability. We conducted a randomized controlled trial to examine the effects of an awareness-raising intervention on meat consumption. We randomized undergraduate classes into treatment and control groups. Treatment groups received a 50-minute lecture on how food choices affect climate change, along with information about the health benefits of reduced meat consumption. Control classrooms received a lecture on a placebo topic. We analyzed 49,301 students’ meal purchases in the college dining halls before and after the intervention. We merged food purchase data with survey data to study heterogenous treatment effects and disentangle mechanisms. Participants in the treatment group reduced their purchases of meat and increased their purchases of plant-based alternatives after the intervention. The probability of purchasing a meat-based meal fell by 4.6 percentage points (p < 0.01), whereas the probability of purchasing a plant-based meal increased by 4.2 percentage points (p = 0.04). While the effects were stronger during the semester of the intervention, dietary shifts persisted and remained statistically significant through the full academic year. Our study provides evidence that an intervention based on informing consumers and encouraging voluntary shifts can effectively reduce the demand for meat. Our findings help to inform the international food policy debate on how to counter rising global levels of meat consumption to achieve climate change goals. To our knowledge, our study is the first to assess the effectiveness of an educational intervention to reduce meat consumption using such high-quality data (i.e. individual-level food purchases) over a prolonged period.