Nudging Healthier Dietary Habits: Evaluation of a Supermarket Placement Strategy in the WRAPPED Study

WRAPPED2 (Women's Responses to Adjusted Product Placement and its Effects on Diet - 2) is a natural experiment with a prospective matched controlled cluster design. The setting is a discount supermarket chain in the United Kingdom regularly used by disadvantaged families for their main shop. The intervention is a store refurbishment programme that involves creation of a new fresh fruit and vegetable section in the store entrance. Control stores keep the existing layout with a limited range of fresh fruit and vegetables and placement of fresh fruit and vegetables at the back of the store.

A total of 45 participants will be recruited from each of 18 intervention and 18 matched control stores through the retailer's loyalty card scheme (postal letter) and shop floor recruitment; these methods proved effective during the pilot. Participants will be women aged 18-45 years who shopped at a study store in the 12 weeks before recruitment. This study is unique in its collection of individual level sales data, as well as demographic and dietary information, and is the first to collect outcome data for more than one family member. Participant's weekly sales data will be obtained through the retailer's loyalty card scheme and will cover 3 months before refurbishment, plus 0-3 months and 3-6 months after. Change in women's fresh fruit and vegetable purchasing from baseline to 3 months is the primary outcome. Secondary outcome data about women's diets, their young child's diet (2-6 years), food shopping habits, perceptions of supermarket environment, and psychosocial and demographic characteristics will be collected by telephone survey before refurbishment, and 1, 3 and 6 months after. Weekly sales data for study stores will be provided by the retailer.

Cost-effectiveness will be assessed from individual, retailer and societal perspectives. Process evaluation will assess implementation, mechanisms of impact and context.

This study is politically and scientifically important being one of the first field studies of this kind. The findings could provide strong evidence for future public health policy interventions to help address inequalities in diet and non-communicable disease risk by supporting development of a healthy store layout that could be adopted more widely in food retail outlets.