The effect of eco-labels and price discounts to promote sustainable food purchases on the nutritional content of online grocery purchases in the UK: a randomised controlled trial. Writing up stage

with Helena Bentil, Oyinlola Oyebode, Edward Hillier, Peter Scarborough, Martin White, Claire Thompson, Jessica Brock, Michael Clark, Anoushka Kumar, Theresa Marteau, Jean Adams and Thijs van Rens 

Abstract:

Background and objectives: Effective interventions are needed to promote both sustainable and healthier food choices. However, interventions aimed at promoting sustainable food purchasing could also support better nutritional outcomes or have unintended negative side effects. Using an online grocery shop, which offers a way to study and evaluate these interventions on a large scale, we assessed the effect of eco-labels and price discounts on the nutritional content of shopping baskets in a real online supermarket in the UK.

Methods: Participants were recruited from the UK Prolific panel and randomly assigned to one of six groups in a 2x3 factorial design. The interventions included: (i) eco-labels, which displayed the environmental impact of products on a scale from A (lowest impact, most sustainable) to G (highest impact, least sustainable), and (ii) price discounts (£1, £0.50, or no discount) offered on more sustainable alternative products that were in the same or a better category for fat (including saturated fat), sugar, and salt content on the traffic-light label for <3 items in their basket. Nutritional outcomes measured included energy (KJ/100g), fat, sugar, salt, and saturated fat (all in g/100g). Regression analysis was used to assess the effect of the interventions on these nutritional outcomes.

Results: A total of 1,426 participants who shopped at least once were included in the analysis. The eco-labels had a very small, non-statistically significant effect on the nutritional content of baskets, with increases in sugar (b = 0.183, p = 0.39), fat (b = 0.053, p = 0.79), saturated fat (b = 0.107, p = 0.32), and energy (b = 10.461, p = 0.30), and small, non-significant decreases in salt (b = -0.017, p = 0.72). Similarly, the £0.50 discount showed small, non-significant effects on sugar (b = -0.263, p = 0.30), salt (b = -0.035, p = 0.49), saturated fat (b = -0.114, p = 0.34), energy (b = -10.594, p = 0.24), and fat (b = -0.054, p = 0.79). The £1 discount also did not appear to affect the nutritional content of purchases [sugar (b = 0.091, p = 0.73), salt (b = 0.025, p = 0.70), and fat (b = 0.023, p = 0.92)], except that energy purchased may have been slightly lower (b = -7.280) but this difference was also not statistically significant (p=0.07).

Conclusions: Eco-labels and price discounts did not lead to statistically significant changes in nutritional outcomes. These findings suggest that further research is needed to explore the potential effectiveness of such interventions in promoting healthier food choices.