Evaluation of Interventions in Online Grocery Shopping for Sustainability and Health: An Adaptive Design Randomized Controlled Trial

Effective interventions are needed to promote more sustainable and healthier food choices for both human and planetary health. This study will evaluate two interventions in two independent adaptive design randomised controlled trials (one 2-arm and one 3-arm trial) within the same study population (a factorial design is not powered). The interventions are (i) eco-labelling, which will provide participants with information on the environmental impact of their food purchases using a score ranging from A (most sustainable) to G (least sustainable); and (ii) price discounts on alternative products with a better sustainability profile (and equal or better nutritional profile) in place of specific products in their basket. To implement these interventions, we will use a browser extension on online shopping websites for one or multiple large UK supermarkets, accessed using the Google Chrome browser on a desktop or laptop computer. We will assess the effect of these interventions on the average eco-score of the basket (primary outcome) as well as its nutritional content (secondary outcome). Health outcomes of the intervention will be modelled using nutrition scores.