Impact of altering the available food options on selection: potential mediation by social norms

Background: Increasing the availability of lower energy foods increases their selection. The current studies examine the extent to which this effect could be mediated by social norms – assessed by perceived popularity of foods – which may be implied by their relative availability. Methods: Study 1 (Online): 2340 UK adults estimated the perceived popularity of lower energy products. For each of eight trials, participants were randomised to one of six groups (between-subjects 3x2) to see photos of cafeteria shelves varying in the availability of lower energy options (1/4 lower energy; 1/2 lower energy; 3/4 lower energy) and fullness of shelves (fuller; emptier).Study 2 (Laboratory): 139 English adults were asked to select a snack. Participants were randomised to select from trays varying in the availability of the lower energy option (1/3 lower energy; 2/3 lower energy) and fullness of tray (fuller; emptier). Results: Study 1: Evidence for an interaction was found, such that when shelves were full, a higher proportion of lower energy options led to greater perceived popularity of lower energy products (1/4 lower energy: 40.9% (95%CIs: 40.1,41.8); 3/4 lower energy: 47.2% (46.3,48.0)), whereas when shelves were emptier, a higher proportion of lower energy options led to lower perceived popularity (1/4 lower energy: 48.4% (47.5,49.2); 3/4 lower energy: 39.2% (38.3,40.0)).Study 2: When the tray was fuller, participants were more likely – albeit non-significantly (main effects: p=0.05; interactions: p=0.07) – to select a lower energy snack when 2/3 of the available snacks were lower energy (35.7% (18.5,52.9)) than when 1/3 were lower energy (15.4% (4.2,26.5)). For emptier trays, lower energy selections decreased as the relative availability of lower energy snacks increased (1/3 lower energy snacks: 36.0% (17.9,54.1); 2/3 lower energy snacks: 27.8% (13.9,41.7)). Conclusions: These studies provide novel evidence that social norms may mediate the impact of availability on food selection. In addition, they suggest that the effect of availability may vary in different contexts, moderated by display layout through its impact on perceived product popularity. Trial registration. ISRCTN: ISRCTN10512908; 31/01/2020