Validation of a digital photography method for assessing plate waste in an acute care hospital setting

Purpose

Routine, systematic measurement of food waste in acute care hospitals is challenging, particularly when monitoring plate waste at scale. This study examines the accuracy of a digital photography method for measuring aggregate solid-food plate waste across hospital mealtimes, with the aim of determining its suitability as a practical, scalable tool for ongoing monitoring.

Design/methodology/approach

Plate waste was assessed across seven breakfasts (n = 108), 21 lunches (n = 804) and 21 dinners (n = 851), reflecting the full hospital menu cycle (one-week rotation for breakfast and three-week rotation for lunch and dinner). For each meal, waste was measured using both direct weighing and visual estimation based on a 7-point scale applied to pre- and post-consumption photographs. Waste quantities for individual solid-food components were calculated by multiplying visually estimated leftovers (%) by standard serving sizes. Agreement between methods was assessed using Bland-Altman plots and Spearman correlation.

Findings

Digital photography estimates showed a strong positive correlation with direct weighing across all mealtimes (rs = 0.9895, p < 0.001), with consistently high agreement at breakfast, lunch and dinner (all p < 0.001). Overall, the mean difference between methods was 4.67 g, with limits of agreement from −50.51 to 59.84 g. Breakfast showed the highest accuracy, while lunch and dinner showed slightly wider limits. Findings support digital photography as a valid and efficient alternative to direct weighing for monitoring solid-food plate waste, with greatest accuracy at breakfast.

Originality/value

Digital photography offers practical advantages by reducing labour, time and spatial requirements, supporting its feasibility and sustainability for routine plate waste monitoring.