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

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. Study 1 (Online): 2340 UK adults estimated the perceived popularity of products. Participants were randomised 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). In Study 1, evidence for an interaction was found, such that when shelves were fuller, 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)). In Study 2, when the tray was fuller, participants were more likely - albeit non-significantly - 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)). 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 be moderated by display layout through its impact on perceived product popularity.