Effect of a default portion-size reduction on meat consumption and diner satisfaction: Controlled experiments in Stanford University dining halls

Reducing animal-based food consumption, especially in Global North countries such as the United States, is an important factor in mitigating the climate and biodiversity crises and improving public health and animal welfare. Choice-architecture interventions or nudges that target the decision structure of consumers, especially within the food domain (e.g., reducing default portion sizes), have outperformed other intervention categories in most studies. Yet the evidence for nudging effectiveness is limited in large-scale, real-life settings, and little is known about effects on diner satisfaction and about backfiring effects that reduce or even reverse the desired behavior. Indeed, concern about the latter two has been a substantial barrier to scalability and wider adoption by the food service industry. In our single-blinded, quasi-experimental, and pre-registered studies in university dining halls, reducing the size of spoons used to serve meat by 25% resulted in ~24 lbs (18%) less meat consumed per day (Study 1, made-to-order burritos) but with a wide confidence interval that included the null. This intervention did not reduce diner satisfaction. Surprisingly, a more substantial 50% reduction in serving spoon size (Study 2, varying menu items) did not reduce consumption, triggered backfiring effects, and significantly decreased diner satisfaction. Internal meta-analysis indicated that on average, the two interventions reduced daily meat consumption by ~12 lbs with a small effect size (standardized mean difference= 0.24), but again with a wide confidence interval that included the null. Key differences in contextual nuances and factors may help explain these mixed results and underscore the importance and challenges of finding the ‘Goldilocks’ zone for successful portion size default nudges. Future research exploring different menu items and in different dining hall stations and food service industry models beyond staff-served is suggested to continue disentangling the nuances of these types of nudges in service of collective, societal-level sustainable diets.