Rethinking social influence on food choices: behavioural pathways from consumption to waste

The transition toward sustainable and healthy food systems requires a deeper understanding of how social influences shape individual food choices within complex food environments. This thesis investigates whether and under which conditions social norms can support healthier and more sustainable eating behaviours. The research adopts an integrated multi-method design that combines a systematic review and meta-analysis, agent-based scenario modelling, and a cluster randomized controlled trial conducted in Italian primary schools. The first chapter synthesizes existing evidence to assess the effectiveness of social norm interventions in shaping eating behaviours and identifies key moderating factors. The second chapter applies a validated agent-based model to simulate behavioural responses to nudging strategies in an all-you-can-eat buffet context, exploring how social norms interact with individual characteristics and sequential decision-making processes. The third chapter evaluates a participatory descriptive social norm intervention aimed at reducing vegetable plate waste in primary school canteens. Results indicate that social norms exert a small but statistically significant influence on eating behaviours, with effects moderated by age, message framing, and behavioural observability. Simulation findings suggest that behavioural interventions interact with multiple behavioural drivers along decision pathways, often generating compensatory responses that limit overall waste reduction. Evidence from the field experiment shows no average reduction in vegetable plate waste, although heterogeneous and context-dependent responses emerge across settings. The findings suggest that social norms should not be considered stand-alone policy instruments but rather complementary tools whose effectiveness depends on environmental design and population characteristics. By integrating evidence synthesis, behavioural modelling, and field experimentation, this research advances theoretical understanding of social influence and provides practical guidance for designing interventions that promote healthy and sustainable eating.