Reducing the climate impact of food choices with comparable nutritional quality: a randomised trial

Abstract Background Diets largely contribute to the global disease burden, and a third of global warming emissions. We assessed the climate footprint reduction effect of framing the climate impact of diets as a collective action problem (social dilemma), compared or in combination with a reflective intervention (information) and a choice architecture intervention (nudge). Interactions with lifestyle factors were examined. Methods A randomised 2X2X2 between-subjects online experiment was conducted among university students ≥18 years, enrolled at a Swiss university, and not following a medically prescribed diet. The outcome was the mean climate footprint of food choices (in kg CO2-eq), based on a Life Cycle Assessment. Meals varied in climate footprints while adhering to the Swiss dietary guidelines. Results This analysis focused on the subset of meat eaters (n = 1691). Median age was 24 years, and 59.85% (n = 1012) were female. Seven intervention groups resulted in significantly lower climate footprints compared to the control. The social dilemma plus a nudge menu was the most effective behavioural intervention leading to 20.20% footprint reduction (b = -1.20 kg CO2-eq) compared to the control group (Mcontrol=5.94, SDcontrol=2.76; Mdilemma+nudge=4.74, SDdilemma+nudge=2.09 t(436) = -5.10, p < 0.001). Lifestyle factors linked to a higher climate footprint of food choices included adhering to a low-calorie diet (b = 1.21 kg CO2-eq, p < 0.05), or a muscle gain diet (b = 2.12 kg CO2-eq p < 0.05) and practising physical activities (PA) while adhering to a muscle-gain diet (Aerobic/Cardio: 3.82 kg CO2-eq, p < 0.05; Muscle-strengthening: 2.24 kg CO2-eq, p < 0.05). Conclusions The combination of reflective collective action communication and menu nudges is an effective strategy to mitigate the climate footprint of food choices in education institutions. Adherence to a muscle-gain diet was identified as a critical but manageable lifestyle factor linked to a higher climate footprint. Key messages • The dilemma plus a nudge was the most effective to reduce the climate footprint of food choices. • This combined intervention can manage the high climate footprints linked to lifestyle factors.