Fostering legume purchases with behavioural interventions: evidence from field experiments in online and offline supermarkets

• Food policies promote plant-based protein; intake remains far below recommendations. • Supermarkets offer a promising setting to increase plant-based protein consumption. • Studies tested interventions in online and physical retail environments. • Legume sales increased with placement and recipe-based in-store interventions. The protein transition is a crucial element of the transition to sustainable food systems, and both EU and national policies aim to foster the consumption of plant-based proteins. Supermarkets as the primary source of food products in many countries represent a promising environment for translating these policy objectives into practice. With three studies from Denmark, including a representative online survey (n = 838 participants) followed by randomised controlled trials in a real online supermarket in two rounds over 6 weeks (n = 9,093 transactions Round 1; n = 8,706 transactions Round 2) and field experiments in physical brick-and-mortar stores (9 test stores, 13 control stores, 21 days of observation), this research investigates the potential of leveraging behavioural interventions to foster legume purchases in online and offline retail settings. The randomised controlled trials in the online supermarket showed that placement interventions in the vegetable section were effective in increasing sales of legumes by 57%, while placement interventions in the meat section were not effective, suggesting that the strategies known to work for highly processed plant-based meat substitutes cannot be translated to legumes. The field experiments in brick-and-mortar supermarkets confirmed that the vegetable section is a promising intervention point. The multi-layered intervention tested (bundling placement combined with a recipe inspiration poster) significantly increased legume purchases to a similar degree as in the other study. This paper concludes that retailers play a pivotal role in the protein transition; however, their commercial interests may impede the implementation of ambitious in-store interventions promoting legumes, highlighting the need for innovative policy approaches.