A Health-Promoting Land of Cockaigne: The influence of nudging and pricing strategies in the supermarket to promote healthy choices and reduce socioeconomic inequalities in diets

This doctoral thesis was aimed to investigate the influence of nudging and pricing strategies in the supermarket to promote healthy choices and improve dietary patterns, to ultimately reduce socioeconomic inequalities in dietary patterns and CMD risk. The first objective was concentrated on better understanding determinants of dietary guideline adherence among Dutch adults with varying socioeconomic backgrounds, and how to recruit such a socioeconomic diverse study population for new lifestyle programmes. The second objective was focused on what type of, and in which combination, nudging and pricing strategies can be effective in the promotion of healthier purchases via different simulated and real-life intervention studies across different food groups. The third objective was related to the design, conduct and recruitment insights of the real-life Supreme Nudge parallel cluster-randomised controlled supermarket trial, and explores differential effectiveness of nudging and pricing strategies on dietary guideline adherence across individuals with varying psychosocial characteristics. Important determinants for higher dietary guideline adherence were higher levels of cognitive restraint of eating, higher habit strength related to vegetable consumption, better cooking skills, and higher frequency of home cooking. Results also revealed that, to improve dietary guideline adherence, there is a need to target the formation of new (healthier) dietary habits which can be easily incorporated into daily routines, and to address food prices by making healthy products more affordable and accessible (Chapter 2). Chapter 3 provided a qualitative overview of opinions from experts with hands-on experiences on how to successfully recruit adults with a low SEP into community-based lifestyle programmes. Results showed that success factors could be structured in five levels, which are presented in this thesis. Three experimental studies were conducted to generate insights into which (combinations of) supermarket interventions and across which food groups they can be effective on promoting healthier purchasing behaviours. The findings from three chapters (Chapter 4-6) combined show that salience nudges and information nudges can enable a modest shift from unhealthier to healthier product purchases and especially within the groups of dairy and grain products, and that this effect can be further enhance when combined with salient pricing strategies. As such, to facilitate a shift in purchasing habits towards healthier patterns, most impact can be generated when different types of nudges and pricing strategies are implemented simultaneously and across various food groups. Chapter 7a presents the study protocol the Supreme Nudge parallel cluster-randomised controlled supermarket trial. This trial implemented nudging and pricing strategies in a real-life supermarket setting to promote healthy purchases, combined with a smartphone app which promotes healthy walking behaviours. A protocol erratum accompanied the initial protocol (Chapter 7b). Chapter 8 provided insights in the participant recruitment costs and inclusion rates of the Supreme Nudge trial participants. Last, the effects of investigated nudging and pricing strategies on dietary guideline adherence were equal for most types of individuals with different psychosocial characterises (Chapter 9). Findings from this doctoral thesis contribute to the growing evidence base that nudging and pricing strategies can be part of a comprehensive set of policy measures to promote a shift towards healthier dietary patterns on a population level. A novel aspect of the work presented is that nudging and pricing strategies seem in effective in promoting healthy purchases within the food groups dairy and grain products, which warrants future evaluation in real-life purchasing settings. Findings from the Supreme Nudge trial will ultimately provide insight into the potential differential effects of nudging and pricing strategies across individuals with different educational attainments, and provide indications on the equity of nudging and pricing strategies and its impact on cardiometabolic risk.