Randomized trial evaluating the effectiveness of within versus across-category front-of-package lower-calorie labelling on food demand

BACKGROUND: Several front-of-pack (FOP) labels identify healthier options by comparing foods within product categories. Alternative approaches label healthier options by comparing across categories. Which approach is superior remains unknown. The objective of this study was to test the effect of a within-category versus across-category FOP lower calorie label on 1) the percentage of labeled products purchased, 2) several measures of calories purchased (total, per dollar and per serving), and 3) total spending. We also tested the moderating effects of hunger and mood on purchasing patterns. METHODS: Using an online grocery store, we conducted a 3 × 3 crossover trial involving actual purchases with 146 participants randomly exposed to: 1) no labeling control; 2) within-category lower calorie labels, and; 3) across-category lower calorie labels. We labeled the 20% of products with the lowest calories per serving within or across categories. Purchases were compared using a fixed effects regression on first-differenced outcomes. RESULTS: Relative to the control condition, there was a 3 percentage point increase (p = 0.01) in labelled products purchased in the within-category arm and a non-significant decrease of 1 percentage point (p = 0.711) in the across-category arm. There was no significant difference in the proportion of labeled products purchased between the two labelling conditions. Neither strategy resulted in reductions in any measure of calories purchased or in total spending. When limited to beverages, there was a 398 cal reduction (p = 0.01) in the within-category arm and a 438 cal reduction (p < 0.01) in the across-category arm versus the control. Mood and hunger did not modify the effects for either strategy. CONCLUSIONS: Results provide evidence that both labelling strategies have the potential to influence food purchasing patterns. However, we cannot definitely state that one labelling approach is superior or even that an increase in the proportion of labelled products purchased will lead to a reduction in calories purchased. TRIAL REGISTRATION: The American Economic Association’s registry for randomized controlled trials, RCT ID: AEARCTR-0002325; Prospectively Registered October 06, 2017. In compliance with ICMJE policy, the trial was also registered on Clinicaltrials.gov, RCT ID: [NCT04165447]. Retrospectively Registered 11 November 2019.