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Address correspondence to: Carmen Byker Shanks, PhD, RDN, Department of Health and Human Development, Montana State University Food and Health Lab, 960 Technology Blvd, Room 215, Bozeman, MT 59718.
Food waste studies have been used for more than 40 years to assess nutrient intake, dietary quality, menu performance, food acceptability, cost, and effectiveness of nutrition education in the National School Lunch Program (NSLP).
Objective
Describe methods used to measure food waste and respective results in the NSLP across time.
Methods
A systematic review using PubMed, Science Direct, Informaworld, and Institute of Scientific Information Web of Knowledge was conducted using the following search terms: waste, school lunch, plate waste, food waste, kitchen, half method, quarter method, weight, and photography. Studies published through June 2015 were included. The systematic review followed preferred reporting items for systematic reviews and meta-analyses recommendations.
Results
The final review included 53 articles. Food waste methodologies included in-person visual estimation (n=11), digital photography (n=11), direct weighing (n=23), and a combination of in-person visual estimation, digital photography, and/or direct weighing (n=8). A majority of studies used a pre–post intervention or cross-sectional design. Fruits and vegetables were the most researched dietary component on the lunch tray and yielded the greatest amount of waste across studies.
Conclusions
Food waste is commonly assessed in the NSLP, but the methods are diverse and reporting metrics are variable. Future research should focus on establishing more uniform metrics to measure and report on food waste in the NSLP. Consistent food waste measurement methods will allow for better comparisons between studies. Such measures may facilitate better decision making about NSLP practices, programs, and policies that influence student consumption patterns across settings and interventions.
The NSLP aims to offer balanced meals to schoolchildren, provided at free or reduced costs for low-income populations and subsidized by the federal government.
The Healthy Hunger Free Kids Act of 2010 required updated nutrition standards for schools based on the most recent Dietary Guidelines for Americans and Institute of Medicine recommendations.
The requirements consist of five meal components: fruits, vegetables, whole grains, low-fat dairy, protein, and sodium content in a specified range. The serving size and caloric limits for each meal for children enrolled in grades kindergarten through 12 are based on age group. A lunch provided to a student must consist of three out of the five components offered to be considered a reimbursable meal, with one of the components being a fruit or vegetable.
The NSLP setting provides an important opportunity for researchers and practitioners to study how much and what types of nutrients children consume and waste. The lunchroom is experimental in nature because menus are designed (and can be changed) by local school food authorities per national nutrition standards, food portions are standardized, and many students dine in the cafeteria every school day. Study results with high external validity have far reaching implications for the NSLP nationwide.
researchers have used plate and food waste studies to observe nutrient intake, dietary quality, menu performance, food acceptability, cost, and effectiveness of nutrition education in the NSLP. Plate and food waste are used synonymously throughout most of the school foods research literature and will herein be referred to as food waste. Food waste studies measure the uneaten edible portion of food served to an individual.
including the amount of a specific nutrient available, consumed, and wasted, the types of food groups most likely being eaten or thrown away, compliance with nutrition practices and policies, the effect of nutrition education on food choice and consumption, acceptability of menu items, and the influence of waste on an institution’s budget and on natural resources. The resulting data can be used to drive important changes in practices, programs, and policies in a school lunch program. In addition, in recent years, global and national food waste campaigns have further amplified the importance of reducing food waste.
The purpose of this systematic review was to provide a summary of the literature describing the measurement and results of food waste studies in the NSLP across time.
Methods
Search Strategy
Articles included in this systematic literature review were extracted from PubMed, Science Direct, Informaworld, and ISI Web of Knowledge using the preferred reporting items for systematic reviews and meta-analyses (PRISMA) format published through June 2015.
When testing key words, these databases yielded relevant articles. The authors tested potential key words related to NSLP and food waste through mock searches to ensure that the final list of terms captured relevant articles that met inclusion and exclusion criteria. Keywords entered with Boolean operators included waste, school lunch, plate waste, food waste, kitchen, half method, quarter method, weight, and photography. The following are two search strategies used in Science Direct: waste OR “food waste” OR “plate waste” OR “kitchen waste” AND school AND lunch; waste OR “food waste” OR “plate waste” AND school AND lunch AND “quarter method” OR “half method” OR weight OR photography. No limits or filters were used in the search. The search strategy was modified for individual databases.
Study Selection
The main criterion for inclusion was the explicit use and description of a method to measure food waste in the NSLP. Articles included were peer-reviewed, written in the English language, and based on studies conducted in the United States covering the NSLP. Journal articles that collected primary data were considered. Articles were excluded in cases where they did not focus on the NSLP, were conducted outside of the United States, did not measure food waste, or presented a review of literature. Meeting abstracts were excluded due to limited information about methodology conducted. Cross-sectional, intervention, quasiexperimental, randomized controlled trial, and mixed-methods study designs and methods were considered.
Data Extraction
Two reviewers first evaluated articles by titles, abstracts, and key words. In cases where food waste and kindergarten through 12th-grade schools were discussed in the title of an article, abstract, or key words, the full article was reviewed to determine relevance. Titles and abstracts that met the inclusion criteria were recorded for full text review. The references in each article included were reviewed to determine whether any other additional studies were relevant, although no additional articles were found that were not already captured in the search. The authors reviewed each article independently and met to determine inclusion or exclusion; disagreements were resolved via discussion.
For each article included in the review, one coder collected and entered data into an extraction template. Information recorded included: first author and year published, purpose, study design and specific data collection method, school type, number of schools involved, location of school, number of students, free and reduced NSLP eligibility, race/ethnicity, grade level or age, dietary component measures, duration and frequency of the data collected, food waste results, other relevant findings to food waste, and whether conducted before or after implementation of the NSLP standards updated by the Healthy Hunger Free Kids Act of 2010. The categories for data extraction were determined based on factors that may inform a researcher’s decision to select a particular food waste measurement method. For example, it may be useful for researchers to understand the various ways results are reported when using a particular method (ie, waste of nutrients, specific foods, or food groups). The data collected, along with the publication, were reviewed by at least two additional coders to ensure accuracy; all disagreements were resolved by discussing inclusion and exclusion criteria to reach consensus.
Quality Appraisal of Individual Studies
Study quality was assessed using the Effective Public Health Policy Project (EPHPP) Quality Assessment Tool.
The EPHPP Quality Assessment Tool provides researchers with criteria to evaluate studies on the basis of selection bias, study design, confounders, blinding, data collection methods, withdraws and dropouts, intervention integrity, and analysis. Each criteria is scored numerically according to provided guidelines by the EPHPP Quality Assessment Tool as strong (score=1), moderate (score=2), or weak (score=3). Subsequently, the entire article is rated as strong (no weak ratings), moderate (one weak rating), or weak (two or more weak ratings).
This study was exempt from institutional review board review because there was no interaction with human subjects.
Results
A total of 10,892 articles were retrieved using the database search. After eliminating duplicates and articles that did not meet inclusion criteria based on title and abstract screening, 66 articles remained for content review. After reviewing the full articles, 13 studies were excluded due to the following reasons: four were conducted outside of the United States; four did not involve the NSLP; three were in preschools; and two were conference abstracts, not full articles (see the Figure).
FigurePreferred reporting items for systematic reviews and meta-analyses (PRISMA) 2009 flow diagram for selecting studies to include in the systematic review of food waste in the National School Lunch Program across time. Terms used in this search included a combination of the following: waste, school lunch, plate waste, food waste, kitchen waste, half method, quarter method, weight, and photography. aRelevance determined by inclusion and exclusion criteria. Inclusion criteria for articles were peer reviewed, English language, and conducted in US National School Lunch Program (NSLP). Exclusion criteria for articles were no focus on the US NSLP, food waste not used as a measurement tool, review of literature, or a conference meeting abstract. ISI=Institute for Scientific Information.
The 53 studies included in this review used four major types of food waste measurement methodologies: in-person visual estimation (n=11) (Table 1), digital photography (n=11) (Table 2), direct weighing (n=23) (Table 3), and a combination of in-person visual estimation, digital photography, and/or direct weighing (n=8) (Table 4). With regard to study design and methods, most studies identified interventions with a pre–post or pre–post-follow-up design (n=20) or cross-sectional (n=23), two were quasiexperimental, two were mixed methods, one study was longitudinal, and five were randomized controlled trials. Fourteen studies were rated as strong, 20 studies were rated as moderate, and 19 studies were rated as weak according to the EPHPP Quality Assessment Tool. Studies labeled as moderate were likely to have a weak rating for study design, whereas studies labeled as weak were likely to have weak ratings for selection bias or confounders and study design. See Table 1, Table 2, Table 3, Table 4 for quality assessment ratings.
Table 1In-person visual estimation through observation for food waste studies conducted in the National School Lunch Program
In some cases, the average percent waste within a dietary component was reported within the cited article. In other cases, this study’s authors calculated average percent wasted within a dietary component when research design collected waste across multiple intervention periods. When percent consumed was reported (instead of percent waste), this study’s authors calculated average percent waste by subtracting the percent consumed from 100% and, if necessary, averaged across multiple intervention periods or groups.
a Data were collected to assess food waste after new school lunch meal patterns were implemented beginning 2012.
b I=intervention.
c Pre-post-follow-up intervention.
d CS=cross-sectional.
e Pre-post intervention.
f RCT=randomized controlled trial.
g ½=half waste method.
h A + sign was recorded for more than half of food wasted and – sign was recorded for less than half of food wasted.
i 6=six-point scale scored as 1=ate all of food to 6=ate none of food.
j E=estimation.
k Measured with 6-point scale: 5=91% to 100%; 4=76% to 90%; 3=51% to 75%; 2=26% to 50%; 1=11% to 25%; 0=0% to 10%.
l Measured in increments of ½ a serving.
m ¼=quarter waste method.
n Measured in increments of none, ¼, ½, ¾, or all wasted.
o NR=not reported with specificity.
p In some cases, the average percent waste within a dietary component was reported within the cited article. In other cases, this study’s authors calculated average percent wasted within a dietary component when research design collected waste across multiple intervention periods. When percent consumed was reported (instead of percent waste), this study’s authors calculated average percent waste by subtracting the percent consumed from 100% and, if necessary, averaged across multiple intervention periods or groups.
q ◊=study indicated dietary component measured but not average percent wasted within dietary component.
r Specific macro- and/or micronutrients measured in whole meal.
s Measured waste of a mixed entrée.
t Measured waste of legumes.
u Data calculated as number of days reported for study multiplied by number of schools involved in food waste collections.
v Data reported according to study as individual food items or entire student tray.
Impact of a Smarter Lunchroom intervention on food selection and consumption among adolescents and young adults with intellectual and developmental disabilities in a residential school setting.
Digital photography assessment of 1,750 elementary and middle school student lunch meals demonstrates improved nutrition with increased exposure to hands-on cooking and gardening classes.
PI=percent increments, meaning percent increments (eg, in 10% or 25% increments) of food selection and plate waste in photograph compared with reference photographed and weighed portion.
In some cases, the average percent waste within a dietary component was reported within the cited article. In other cases, this study’s authors calculated average percent wasted within a dietary component when research design collected waste across multiple intervention periods. When percent consumed was reported (instead of percentage waste), this study’s authors calculated average percent waste by subtracting the percent consumed from 100% and, if necessary, averaged across multiple intervention periods or groups.
a Data were collected to assess food waste after new school lunch meal patterns were implemented, beginning 2012.
b CS=cross-sectional.
c Cross-sectional study used for validation purposes.
d RCT=randomized controlled trial.
e I=intervention.
f Pre-post intervention.
g RP=raw percent, meaning percent of food selection and plate waste in photograph compared with reference photographed and weighed portion.
h PI=percent increments, meaning percent increments (eg, in 10% or 25% increments) of food selection and plate waste in photograph compared with reference photographed and weighed portion.
i NR=not reported with specificity.
j Data calculated as number of days reported for study multiplied by number of schools involved in food waste collections.
k ◊=study indicated dietary component measured but not average percent wasted within dietary component.
l Fruits and vegetables combined.
m Measured waste of a mixed entrée.
n Specific macro- and/or micronutrients measured in whole meal.
o Measured waste of legumes.
p In some cases, the average percent waste within a dietary component was reported within the cited article. In other cases, this study’s authors calculated average percent wasted within a dietary component when research design collected waste across multiple intervention periods. When percent consumed was reported (instead of percentage waste), this study’s authors calculated average percent waste by subtracting the percent consumed from 100% and, if necessary, averaged across multiple intervention periods or groups.
q Data reported according to study as individual food items or entire student tray.
Energy and macronutrient consumption of elementary school children served modified lower fat and sodium lunches or standard higher fat and sodium lunches.
Fruit and vegetable consumption was calculated by weighing all produce prepared and subtracting unserved and waste weights, divided by number of students.
Fruit and vegetable consumption was calculated by weighing all produce prepared and subtracting unserved and waste weights, divided by number of students.
At least one study school was not identified as elementary or middle, but identified kindergarten through eighth grade or was not identified as middle or high, but identified as grades six through 12.
At least one study school was not identified as elementary or middle, but identified kindergarten through eighth grade or was not identified as middle or high, but identified as grades six through 12.
At least one study school was not identified as elementary or middle, but identified kindergarten through eighth grade or was not identified as middle or high, but identified as grades six through 12.
In some cases, the average percent waste within a dietary component was reported within the cited article. In other cases, this study’s authors calculated average percent wasted within a dietary component when research design collected waste across multiple intervention periods. When percent consumed was reported (instead of percentage waste), this study’s authors calculated average percent waste by subtracting the percent consumed from 100% and, if necessary, averaged across multiple intervention periods or groups.
a Data were collected to assess food waste after new school lunch meal patterns implemented beginning 2012.
b Q=quasiexperimental.
c CS=cross-sectional.
d I=intervention.
e Pre-post intervention.
f Pre-post-follow-up intervention.
g L=longitudnal.
h MM=mixed methods.
i RCT=randomized controlled trial.
j DW=direct weighing.
k Difference weight of plate waste for each food minus weight of average selected serving.
l Percent plate waste calculated by dividing the weight of edible food waste by the mean serving weight.
m Difference weight of plate waste for each food minus pre consumption selections for all students’ plates.
n Weight of fluid milk remaining was determined using the full weight and empty container weight of the carton.
o Fruit and vegetable consumption was calculated by weighing all produce prepared and subtracting unserved and waste weights, divided by number of students.
p Waste was sorted by hand and weighed on a digital scale.
q At least one study school was not identified as elementary or middle, but identified kindergarten through eighth grade or was not identified as middle or high, but identified as grades six through 12.
r NR=not reported with specificity.
s In some cases, the average percent waste within a dietary component was reported within the cited article. In other cases, this study’s authors calculated average percent wasted within a dietary component when research design collected waste across multiple intervention periods. When percent consumed was reported (instead of percentage waste), this study’s authors calculated average percent waste by subtracting the percent consumed from 100% and, if necessary, averaged across multiple intervention periods or groups.
t ◊=study indicated dietary component measured but not average percent wasted within dietary component.
u Measured waste of a mixed entrée.
v Specific macro- and/or micronutrients measured in whole meal.
w Data calculated as number of days reported for study multiplied by number of schools involved in food waste collections.
x Data reported according to study as individual food items or entire student tray.
Table 4Combination of methodologies for food waste studies conducted in the National School Lunch Program (visual estimation, digital photography, direct weighing)
Student receptivity to new school meal offerings: Assessing fruit and vegetable waste among middle school students in the Los Angeles Unified School District.
In some cases, the average percent waste within a dietary component was reported within the cited article. In other cases, this study’s authors calculated average percentage wasted within a dietary component when research design collected waste across multiple intervention periods. When percent consumed was reported (instead of percentage waste), this study’s authors calculated average percetage waste by subtracting the percentage consumed from 100% and, when necessary, averaged across multiple intervention periods or groups.
a Data were collected to assess food waste after new school lunch meal patterns were implemented beginning 2012.
b CS=cross-sectional.
c Cross-sectional study used for validation purposes.
d I=intervention.
e Pre-post intervention.
f W=direct weighing.
g VO=visual observation.
h Difference weight of plate waste for each food minus weight of average selected serving.
i Quarter waste method (none, half, three-quarters, or all).
j DP=digital photography.
k Estimate percent of food selected and plate waste in photograph compared with reference photograph or a sample tray.
l NR=not reported with specificity.
m In some cases, the average percent waste within a dietary component was reported within the cited article. In other cases, this study’s authors calculated average percentage wasted within a dietary component when research design collected waste across multiple intervention periods. When percent consumed was reported (instead of percentage waste), this study’s authors calculated average percetage waste by subtracting the percentage consumed from 100% and, when necessary, averaged across multiple intervention periods or groups.
n ◊=Study indicated dietary component measured but not average percentage wasted within dietary component.
o Measured waste of a mixed entrée.
p Specific macro- and/or micronutrients measured in whole meal.
q Data calculated as number of days reported for study multiplied by number of schools involved in food waste collections.
r Data reported according to study as individual food items or entire student tray.
Researchers conducted in-person visual estimation through observation by first viewing several serving sizes of school lunch foods of interest to understand the appearance of the average plated food component. Researchers then weighed several samples of the plated food item of interest to find the average serving weight in grams or ounces. Finally, student trays were collected and assessed for the amount of food wasted in validated increments. Increments included less or more than half wasted,
In some studies, a computer program was used to estimate the grams or ounces and energy of food consumed from the in-person visual estimation through observation.
One study focused on the total amount of food wasted.
Other studies used food waste measurement as a proxy for the amount of foods students consumed. The research had a variety of aims, including to understand the influence of nutrition education
Impact of a Smarter Lunchroom intervention on food selection and consumption among adolescents and young adults with intellectual and developmental disabilities in a residential school setting.
Digital photography assessment of 1,750 elementary and middle school student lunch meals demonstrates improved nutrition with increased exposure to hands-on cooking and gardening classes.
Researchers conducted visual estimation of food waste through digital photography by photographing either or both reference serving sizes of the food component of interest, or the student’s selected food preconsumption. When taking photographs of the reference serving sizes, researchers generally calculated an average weight for the food component as well. Each student’s tray was then photographed at the tray return area (postconsumption). In reviewing the photographs, food consumption was estimated as a percentage of the reference serving size or student’s preconsumption selection. Food waste estimates were made as a raw percent
Digital photography assessment of 1,750 elementary and middle school student lunch meals demonstrates improved nutrition with increased exposure to hands-on cooking and gardening classes.
Impact of a Smarter Lunchroom intervention on food selection and consumption among adolescents and young adults with intellectual and developmental disabilities in a residential school setting.
Computer applications were used to estimate the weight and energy of food consumed from the visual estimation through digital photography in studies using this method.
The purposes of each study varied, with food waste measures aimed at primarily understanding the amount of food waste
Impact of a Smarter Lunchroom intervention on food selection and consumption among adolescents and young adults with intellectual and developmental disabilities in a residential school setting.
Digital photography assessment of 1,750 elementary and middle school student lunch meals demonstrates improved nutrition with increased exposure to hands-on cooking and gardening classes.
Impact of a Smarter Lunchroom intervention on food selection and consumption among adolescents and young adults with intellectual and developmental disabilities in a residential school setting.
Digital photography assessment of 1,750 elementary and middle school student lunch meals demonstrates improved nutrition with increased exposure to hands-on cooking and gardening classes.
Digital photography assessment of 1,750 elementary and middle school student lunch meals demonstrates improved nutrition with increased exposure to hands-on cooking and gardening classes.
reported free and reduced rates near 100%, whereas several other studies did not report free and reduced rates.
As in the studies using visual estimation techniques to measure waste, studies using digital photography also focused predominantly on fruits and vegetables. Several distinguished between forms of fruits and vegetables, such as cooked, raw, canned, and fresh.
Impact of a Smarter Lunchroom intervention on food selection and consumption among adolescents and young adults with intellectual and developmental disabilities in a residential school setting.
Impact of a Smarter Lunchroom intervention on food selection and consumption among adolescents and young adults with intellectual and developmental disabilities in a residential school setting.
Digital photography assessment of 1,750 elementary and middle school student lunch meals demonstrates improved nutrition with increased exposure to hands-on cooking and gardening classes.
Energy and macronutrient consumption of elementary school children served modified lower fat and sodium lunches or standard higher fat and sodium lunches.
The process for direct weighing of food waste generally includes to determine what is being served in the cafeteria on the day of the study, to determine which food(s) will be included in the study, to weigh random samples of the food(s) and calculate an average weight, to collect and weigh food waste from student trays, to calculate percent or grams or ounces consumed by subtracting the food waste collected in Step 4 from the average weight determined in Step 3 and multiplying by 100. Some research measured waste for all foods on the tray,
Energy and macronutrient consumption of elementary school children served modified lower fat and sodium lunches or standard higher fat and sodium lunches.
Three additional studies measured the weight of all food before it was served, collected all food waste from student trays, and subtracted the total amount leftover.
Energy and macronutrient consumption of elementary school children served modified lower fat and sodium lunches or standard higher fat and sodium lunches.
Digital photography assessment of 1,750 elementary and middle school student lunch meals demonstrates improved nutrition with increased exposure to hands-on cooking and gardening classes.
Energy and macronutrient consumption of elementary school children served modified lower fat and sodium lunches or standard higher fat and sodium lunches.
The most common food components examined in studies involving direct weighing were fruits and vegetables. Sixteen studies reported the quantity of waste from fruits and vegetables. Other dietary components examined included milk, grains, and high-protein items such as soy-based products. Studies examined acceptance of specific foods in the cafeteria, such as whole grains.
Many interventions (eg, nutrition education, changes in nutrition requirements, lunchtime procedures or the food environment, or food acceptability on consumption levels) led to a decrease in waste for some foods.
Combination of Methods
Eight studies used a combination of in-person visual estimation through observation, visual estimation through digital photography, and/or direct weighing methods (Table 4).
Student receptivity to new school meal offerings: Assessing fruit and vegetable waste among middle school students in the Los Angeles Unified School District.
Student receptivity to new school meal offerings: Assessing fruit and vegetable waste among middle school students in the Los Angeles Unified School District.
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