Date Published: February 14, 2018
Publisher: Public Library of Science
Author(s): Brian E. Roe, John W. Apolzan, Danyi Qi, H. Raymond Allen, Corby K. Martin, Rebecca A Krukowski.
We analyze food-item level data collected from 50 adults from the United States using the Remote Food Photography Method® to provide the first estimates of plate waste gathered from adults across multiple consecutive meals and days in free-living conditions, and during laboratory-based meals with fixed food items and quantities. We find average plate waste in free-living conditions is 5.6 grams (7.7 kcals) per item and that 3.3% of all food selected is returned as plate waste, where the percent waste figure is substantially lower than previously published plate waste estimates gathered primarily from dine-out settings in the United States such as buffets and institutional settings with limited-choice meals (e.g., school cafeterias). Plate waste from the same participants during the laboratory-based meals is significantly higher with an average of 203.2 grams of solid plate waste per meal (531.3 kcals) or 39.1% of the food provided, which is similar to the plate waste percentages found reported in some school cafeteria settings. The amount of plate waste generated in free-living conditions is significantly positively associated with portion size selected for an item. In a multivariate analysis that controls for macronutrient profile, items selected from the vegetables, fats/oils/dressings, and grains categories are associated with significantly greater amounts of plate waste per item. We find no significant associations between free-living plate waste and gender, age, race or body mass index but find that women leave more plate waste in the lab meal where portion sizes are pre-determined by the researcher and similar for all respondents. We discuss possible implications of these findings for programs focused on reducing plate waste and food waste among consumers.
Countries around the world have resolved to reduce food waste in an attempt to advance food security, environmental sustainability and economic efficiency goals [1–4]. More than 40% of food waste occurs at the retail and consumer level in industrialized economies . Plate waste–food that is served on individual plates but not consumed–is among the largest sources of avoidable food waste generated within households and represents about 30% of all avoidable household food waste in the United Kingdom, the country for which the most detailed analysis of household food waste is currently available [6–7]. Hence, understanding the amount, composition and patterns of plate waste in household settings may provide key insights for addressing the larger issue of avoidable household food waste.
Average per-item plate waste was 5.63g (95% confidence interval 4.13g to 7.12g) and 7.69 kcals (Table 2), which constituted an average of 2.5% of the amount served. 6% of all items served generated plate waste. Of the items served 16% were classified as liquids while 26% were grain products, 20% were meat, poultry, fish and mixtures, 15% milk and milk products, 14% vegetables, 11% sugars, sweets, and beverages and 6% fruits. Figs 1 and 2 display total waste and selection by food category. The greatest waste amounts across the sample are classified as sugars, sweets and beverages (29.5%) followed by grain products (28.8%), meat, poultry, fish and mixtures (15.7%) and vegetables (13.7%). The largest constituent of waste attributable to sugars, sweets and beverages is waste from sugar-sweetened drinks, which constitutes 82% of the waste in this food group in this sample.
The average level of plate waste recorded among the 50 participants in free-living conditions was 2.5% per item selected with a 95% confidence interval of 2.05% to 2.99%. Overall, 3.3% of selected food was left as plate waste. Both of these figures are lower than previously published plate waste estimates featuring adult samples (S1 Table). Qi and Roe  find plate waste of 11% (41g) at a free buffet provided to survey respondents; Wansink and Van Ittersum  estimate plate waste between 8% and 14% among paying customers at an all-you-can-eat Chinese buffet; Just and Wansink  estimate plate waste between 7% and 10% among customers paying half and full price at an all-you-can-eat pizza buffet; Freedman and Brochado  find 18% plate waste for French fries in an all-you-can-eat university dining service; and Norton and Martin  estimate 17% plate waste at a college dining hall. Other university plate waste studies [26–28] yield estimates of the volume of waste in the range of 63g–124g per patron per meal. Hotel breakfast buffet guests are found to generate 15g of plate waste per patron . The lowest point estimate from the reported extant studies is 7%, which is more than double the figures estimated for this sample.
We do not know if the measured plate waste in this study was discarded or stored for future consumption. If a large portion was stored for future consumption and then actually consumed, it would mean that even a smaller portion of served food goes unconsumed than we report. Given this possibility, we advise interpreting the plate waste figures as an upper bound on the amount of food wasted by our sample as plate waste. Further, this study did not capture food waste that occurs during food preparation and via refrigerator/freezer and cabinet cleanouts, discarding spoiled foods, etc.
Our study yields plate waste figures considerably lower than those in the previous published literature. Given the validity of the RFPM® for measuring food selection, plate waste, and food intake, we introduce the possibility that at least one component of total food waste (plate waste from individual eating occasions) is a smaller concern than previous thought and that a larger proportion of food waste occurs during food preparation and through discarding spoiled or unwanted food. Indeed, when our sample consumes a meal served to them in a laboratory setting with fixed quantities, the amount and percent of plate waste is substantially higher than those observed in free-living conditions and more in line with waste rates observed in National School Lunch Program settings where portion sizes and meal content are also not independently determined by the consumer. Our sample is small (n = 50), primarily female and taken from a single region, however, and future measurement is needed to establish more robustly the typical levels and patterns of plate waste generated in a variety of eating occasions and settings. Our finding that plate waste in free-living conditions increases with portion size (grams selected) reinforces results from the literature and suggests that interventions aimed at portion size control may warrant further investigation vis a vis possible implications for household food waste. While this study involved no manipulation concerning portion size, other studies that have manipulated plate size downward in an attempt to reduce portion size  found incidental reductions in plate waste accompanied the reduced portion sizes driven by the manipulation.