Can (dynamic) social norms encourage plant-based food purchases? a quasi-experimental study in real-world Dutch supermarkets

Background:
Communicating (dynamic) social norms is considered a promising tool to stimulate healthy and sustainable food choices. The aim of the present study was to evaluate to what extent a (dynamic) social norm intervention in real-world supermarkets could increase sales (grams per week) of meat alternatives (i.e. meat substitutes and legumes).
Methods:
A quasi-experimental study, including three intervention and three control supermarkets, was conducted during a 12-week period. The intervention supermarkets communicated dynamic norms textually on stickers and banners at different in-store locations (e.g. at the entrance, meat aisles). Moreover, the prominence of meat substitutes was (optically) increased and legumes were conveniently placed near the meat and meat substitutes section. Weekly sales data over a period of 75 weeks were obtained, 62 pre-intervention and 13 during intervention. Comparative interrupted time series analyses were conducted to analyse changes in meat alternative sales (in grams) during the intervention period in the intervention supermarkets compared to pre-intervention sales trends and to control supermarkets. Secondary outcomes included meat sales in grams per week and the ratio of protein content of meat alternatives to protein content of meat sales.
Results:
Average meat alternative sales in weekly grams before the intervention were M = 371,931.2 (SD = 113,055.3) in the control supermarkets and M = 299,012.5 (SD = 91,722.8) in the intervention supermarkets. The intervention did not change meat alternative sales in intervention supermarkets compared to pre-implementation sales trends and to control supermarkets (B = − 685.92, 95% CI [− 9904.8; 8525.7]). Sales of meats were also unaffected (B = − 130.91, 95% CI [− 27,127.50; 26,858.33]), as well as the ratio of protein content of meat alternatives to protein content of meat in grams sold per week (B = − 670.54, 95% CI [− 8990.6; 7644.4]).
Conclusions:
Communicating (dynamic) social norms via textual and environmental cues (i.e. increasing the prominence of meat alternatives in supermarkets) did not increase meat alternative sales nor reduce meat sales. With supermarkets playing an important role in modulating sustainable food choices, more substantial effort or changes are needed to increase plant-based food purchases and lower meat purchases.