BACKGROUND: Weighing an individual's plate waste provides reliable estimates of food intake by physically weighing individual food components to the nearest gram before and after a meal. Weighing aggregate, school-level food waste may be an inexpensive and less time-consuming alternative. However, it has not been determined whether aggregate plate waste is an accurate measure of individually weighed plate waste.
OBJECTIVE: This pilot study aimed to evaluate the accuracy of aggregate plate waste for quantifying food waste in a school cafeteria setting in comparison with individually weighed plate waste.
DESIGN: A pilot validation study in which aggregate plate waste was compared against individually weighed plate waste in a school cafeteria setting.
PARTICIPANTS/SETTING: This study took place in an urban, low-income school district in Massachusetts in the spring of 2014. Four elementary schools with identical cafeterias and meals participated in the study. Approximately 1,700 students participated in this study.
MAIN OUTCOME MEASURES: For individually weighed plate waste, the percent discarded was calculated by dividing the weight of each discarded item by the average weight of the food item served and the percent consumed was calculated as the residual. For aggregate-level measurements, waste was separated by component (entrée, vegetable, fruit, and milk), and the weight discarded was calculated based on the weight of the cumulative amount remaining and an average weight for each food item served, with the percent consumed calculated as the residual.
STATISTICAL ANALYSES PERFORMED: Intraclass correlation coefficients (ICCs) were calculated to assess the agreement between aggregate plate waste and individual-level plate waste values. RESULTS: Agreement was excellent for entrées (ICC=0.90) and vegetables (ICC=0.78), but poor for milk (ICC=0.22) and fruits (ICC=0.23). The overall agreement for all four components combined was excellent (ICC=0.75).
CONCLUSIONS: Results suggest that aggregate plate waste may provide a reasonable estimate of individually weighed plate waste, but additional research is warranted.
