Pledging after nudging improves uptake of plant-based diets: a field experiment in a German university cafeteria

Meat-based diets are carbon-intensive and incompatible with Paris climate targets. Reducing meat consumption is essential to mitigate climate change. Behavioural nudges, which present structured choices to citizens, have been increasingly used to reduce meat demand. But they face ethical challenges and limits when scaling up. We test if encouraging people to reflect after nudging improves the effectiveness of a nudge. We design and administer a novel randomised controlled trial in a German university cafeteria, lasting for five weeks (N_participants = 129,N_meals = 645). In week 1, we measure baseline dietary behaviours. In week 2, we introduce a labelling nudge in the cafeteria. Subsequently, in weeks 3 & 4, we assign participants randomly to three experimental conditions: a control group that continues to receive the labelling nudge and two treatment groups that get the labelling nudge with an opportunity to reflect, either on the nudge (nudge+ 1) or their own preferences (nudge+ 2). All treatments are discontinued in week 5. In the pooled sample, controlling for period fixed effects, we find that the labelling nudge is not associated with meaningful changes in meat-demand over time. Nonetheless, being encouraged to reflect reduces meat-demand significantly compared to the nudge—the nudge+ 1 reduces chances of buying a meat-based item in the cafeteria by 5% (μ = −0.25, 95% CI = [−0.49,−0.36]) whereas the nudge+ 2 reduces it by 7% (μ = −0.35, 95% CI = [−0.61,−0.08]). These treatment effects attenuate when the interventions are discontinued. We recommend that combining reflection with nudging can improve the uptake of climate-friendly diets, at least in the short-term.