Introduction
Globally, there has been an increase in the presence, and use of food delivery platforms [Food prepared outside the home, whether from fast food, takeaway, or full service restaurants is typically greater in energy than food prepared at home [In the UK, public health strategies to improve the nutritional quality of food sold in the out-of-home food sector have been suggested at national and local levels [Non-Governmental Organisations have also urged the UK Government to develop policies to address disproportionate pricing of unhealthy foods [Previous research has assessed the impact of proportional pricing with different foods and beverages in a range of settings and findings are mixed. In a laboratory study, participants were given the option to purchase popcorn with money provided by the researchers [In a study conducted in the Netherlands [It is important to consider how implementing a new policy, such as proportional pricing, would interact with the existing food environment. One study conducted in the US examined the influence of a pricing intervention alongside presence or absence of calorie labelling [Due to the growing popularity of food delivery apps and the need to examine potential interventions to improve dietary choices in this context, the primary aim of the current research was to examine the influence of proportional pricing and calorie labelling interventions, both separately and combined, on portion size choice, calories ordered and monetary value of orders made when selecting food and drinks from three outlet types on a virtual delivery app. Additional aims were to explore whether the effects of proportional pricing and calorie labelling differ according to participant characteristics (i.e. BMI, age, gender, education, ethnicity and food choice motive scores). We hypothesised that there would be a significant impact of pricing strategy, where participants in proportional rather than value pricing conditions would be less likely to choose a larger option, would order fewer calories and spend less money. We also hypothesised that there would be a significant effect of calorie labelling, where participants in calorie labelling conditions would be less likely to choose a larger option, would order fewer calories and would spend less money compared to participants not shown calorie labels. Furthermore, we predicted that the likelihood of choosing smaller options and fewer calories would be most pronounced when participants were provided with both proportional pricing and calorie labels.