Exploring socioeconomic inequalities in healthy and sustainable diets using big data: An observational analysis of loyalty card data from a UK Retailer, 2022

Introduction: Promoting healthier and more sustainable diets is needed to improve population and planetary health. However, limited evidence has described how these intersecting issues vary together by socioeconomic position. Our study uses novel large-scale retailer consumer purchase data, adjusted for known biases, to explore socioeconomic inequalities in health and environmental impacts of food and beverage purchases. Methods: Data were household-level loyalty card records from a major UK supermarket retailer between 24th July and 31st December 2022 (n = 117 710). The health-related outcome was proportion of purchases that were ‘High in Fat, Salt or Sugar’ (HFSS), determined using the UK nutrient profile model. We estimated three environmental outcomes: total greenhouse gas emissions, total land use footprint, and total water use from food purchases. Multilevel regression with post-stratification was used to estimate each outcome measure by level of neighbourhood socioeconomic deprivation, adjusted for age, household size, distance to nearest supermarket, and urbanicity. We also described environmental outcomes by food category across level of deprivation. Results: Households residing in the most deprived 10% of areas purchased a larger proportion of HFSS items than households in the least deprived 10% of areas. Households in the least deprived 10% of areas had a greater absolute environmental impact. However, when considered per weight of items, households in the most deprived 10% of areas purchased items that contributed to higher greenhouse emissions per kg but had lower impacts for land use. Soft drinks, ready meals, pasta, and pastry products were identified as key food categories for targeted ‘food swaps’ to reduce environmental inequalities. Conclusions: Our novel application of retailer loyalty card data shows how these data can offer valuable insights for informing strategies to promote healthy, sustainable, and equitable diets. Tackling environmental inequalities in food purchases requires tailoring approaches to different population groups.