Does the impact of calorie (energy) labelling on food purchased in worksite cafeterias differ by food category? A mega-analysis of field trials.

Calorie labels may help limit energy intake as part of policy efforts to prevent obesity. However, evidence on their effectiveness is mixed. We hypothesised this variability may relate to differences in responsiveness to labelling by food category, e.g., main meals vs. discretionary items (e.g. snacks). Systematic searches identified randomised field studies of calorie labelling that reported energy purchased (kcal) from targeted food and drink categories (main meals, discretionary foods, soft drinks). A mega-analysis (pooling raw data from multiple studies) used generalised linear mixed models (GLMM) to analyse aggregate study data on total energy (kcal) purchased within each food category per week. Three studies provided data from 22 worksite cafeterias for the mega-analysis. When calorie labels were present (versus absent) energy purchased per transaction for main meals increased (18kcal/transaction; 95%CI: 4,31). There was no evidence of differences in energy purchased per transaction from discretionary foods (-10 kcal/transaction; 95%CI: -24,3), or drinks (-2kcal/transaction; 95%CI: -15,12). Previous studies have reported no or small effects from calorie labels. The findings of this study suggest the impact of calorie labels in worksite cafeterias differs by food category, but there was no clear evidence that labels reduced energy purchased in any of the categories.