Combining positioning and labelling interventions for healthier and more environmentally sustainable products: A randomised controlled trial in an online experimental supermarket.

Population diets need to become healthier and more sustainable to limit their negative effects on health and environment. This study assessed the effect of a positioning intervention, in isolation and in combination with a labelling intervention, on the a) healthiness and b) environmental sustainability of food choices in an experimental online supermarket. Participants (n=2220) were randomly assigned to one of five trials groups (control; healthier items shown earlier ("health position"); health position & nutri-score labels; environmentally sustainable products shown earlier ("eco position"); eco position & ecolabels) and completed a shopping task in an experimental online supermarket. Linear regressions showed that compared to control, mean scaled nutri-scores of shopping baskets were significantly lower (healthier) for health position (-2.30; 95%CI: -3.07, -1.52) and health position & labels (-2.50; 95%CI: -3.28, -1.72), with no significant difference between health position and health position & labels (-0.20; 95%CI: -0.66, 0.25). The mean eco scores of shopping baskets were significantly reduced (more sustainable) for eco position (-24%; 95%CIs: -15%, -31%)) and eco position & labels (-30%; 95% CIs: -22%, 37%).) compared to control. The eco position & labels group had significantly lower mean eco scores (-8%; 95% CIs: -2%, -14%) compared to eco position. The positioning intervention improved health and environmental sustainability of food selections in an experimental online supermarket, with less robust evidence for a small additional effect of adding labels. There was no suggestion that adding labels that potentially make the positioning intervention more salient had any backfire effects.