Current levels of meat consumption in developed countries exceed nutritional recommendations and harm the environment. A promising intervention to reduce meat consumption is prompts, that is, reminders to perform a specific behavior in a particular situation. The present study tested a written prompt combined with an adapted version of the visualized Swiss dietary recommendations ‘Swiss Food Pyramid’ in the field. The study was conducted simultaneously in two staff restaurants with a two-week baseline period followed by a two-week intervention period. Participants (n = 131) photographed their food choices in the staff restaurants using a depth camera provided. The amount of meat on their plates was estimated using the automatic volume estimation module by goFOOD™, an artificial intelligence-based automatic dietary assessment system. The results showed that participants in one staff restaurant preferred the vegetarian menu over the meat menu when exposed to the intervention, consequently reducing their meat consumption. The intervention was particularly successful among participants with a positive attitude toward environmental protection and high health consciousness. Participants who enjoyed meat for hedonistic reasons and who ate meat the most frequently were less influenced by the intervention. In the other staff restaurant, the intervention had no effect. Potential reasons are discussed in light of the different clientele of the two staff restaurants.