Weighed Plate Waste Can Accurately Measure Children's Energy Consumption from Food in Quick-Service Restaurants

Background: Quick-service restaurants (QSRs) serve one-third of US children on any given day, yet no methods can directly measure energy (kcal) consumed in QSRs. Weighed plate waste is one feasible option, but the accuracy is unknown. Objective: The objective of this study was to determine the accuracy of weighed plate waste for measuring children's energy consumption in QSRs. Methods: Children's platewaste (entrees and sides) was collected for a larger study assessing a community-wide health messaging campaign to inform parents' orders for children in QSRs; a subsample (n = 194) was used for validation. Gross energy left over estimated by weighed plate waste combined with restaurant-stated nutrition information was compared to gross energy determined by bomb calorimetry, the gold-standard energy assessment technique. Analyses were conducted at the meal level (all food items, combined) and stratified by the number of items per meal (1, 2, or 3). Pearson correlations and paired t tests analyzed agreement; Bland-Altman statistics examined differences between energy estimations for the total and stratified subsample. Results: Overall, significant agreement was observed between weighed plate waste and bomb calorimetry (r = 0.99, P < 0.001). On average, weighed plate waste underestimated energy content by <2 kcal compared with bomb calorimetry (mean percent difference +/- SD of 0.3% +/- 10.7%); 94% of estimations fell within the limits of agreement (-23.5 to 26.8 kcal), and 63% and 24% of estimations differed by <10 or <20 net kcal, respectively. Although stratification by item number showed slight variation, mean differences for all strata were <5 kcal (t test P > 0.80), suggesting the accuracy of weighed plate waste for measuring meals of various sizes. Conclusions: Weighed plate waste is an accurate and valid field technique for measuring children's energy consumption from food in QSRs. Future improvements to capturing beverages, self-serve condiments, and sharing behaviors may improve the overall feasibility and accuracy.