How prompt concreteness shapes consumer food waste in restaurants: evidence from field and laboratory experiments

Introduction The increasing problem of food waste has become a global issue. Displaying prompts to restaurant consumers is widely regarded as an important measure to reduce food waste, though its effectiveness remains debated. Based on this, this study explores the impact of a common design feature of prompts—prompt concreteness—on consumer food waste in restaurants. Methods This study first conducted a field experiment in a Chinese-style casual dining restaurant by placing prompt labels on restaurant tables and weighing customers’ leftover food, providing initial evidence for the effect of prompt concreteness on consumer food waste. Subsequently, this study conducted two laboratory experiments to explore the psychological mechanism and boundary conditions of this effect. Results The field experiment ( N = 261) found that concrete prompts can reduce consumer food waste by an additional 17.2% compared with abstract prompts ( p < 0.001). The first laboratory experiment ( N = 193) confirmed that concrete prompts (vs. abstract prompts) were more effective in increasing consumers’ willingness to take leftovers ( p = 0.003), with moral justification playing a mediating role. Another laboratory experiment ( N = 357) showed that the average weight of food ordered by participants in the concrete prompt group was 10.54% lower than that of participants in the abstract prompt group ( p = 0.008), indicating that concrete prompts can effectively reduce consumers’ over-ordering behavior. Furthermore, this effect disappeared when participants had higher levels of trait reactance. Discussion These findings reveal how the concreteness of prompts influences consumer food waste in restaurants, as well as the underlying mechanisms and boundary conditions. The results provide a scientific explanation for the debate in previous research on prompt effectiveness, and offer valuable insights for marketers to scientifically design and apply prompts to reduce consumer food waste.