2017 Theses Doctoral
A Conceptual Evaluation Framework for Measuring Fruit and Vegetable Consumption at School Lunch among Elementary Students Participating in the National School Lunch Program
In the U.S., few children meet federal recommendations for fruit and vegetable consumption, putting them at increased risk for overweight, obesity and several non-communicable diseases. Interventions to increase fruit and vegetable consumption delivered within the school setting are advantageous in that they provide the opportunity to reach many youths in period of life during which key diet-related behaviors are formed that may track into adulthood. The National School Lunch Program (NSLP), a federal food assistance program that serves over 30 million meals daily in over 100,000 schools in the U.S., is one example of an intervention that may increase fruit and vegetable consumption among children. Recent regulatory changes to the program via the 2010 Healthy Hunger-Free Kids Act (HHFKA) require compliance with minimum daily and weekly minimums for fruit and vegetables offered to students at lunch to receive federal reimbursement, which has resulted in increased availability of fruits and vegetables. Although preliminary evaluations of the regulatory changes have documented small increases in consumption, there is interest in identifying other programs and policies to ensure that components are consumed. Yet there is little meta-evidence that critically examines aspects related to the design of school-based intervention studies assessing fruit and vegetable consumption. This dissertation describes a systematic mapping review of the literature and three empirical studies which inform the development of a conceptual evaluation framework for designing studies to measure fruit and vegetable consumption among elementary students in the U.S. within schools participating in the NSLP.
A systematic mapping review of the literature technique was used to identify studies conducted among elementary students in grades K-5th within schools in the United States in the period from 2004 to present with the primary outcome fruit and vegetable consumption at the lunch meal. A total of 61 records were included in the review, categorized as either methodological validation studies (n=10) or as studies of factors related to students’ consumption of fruits and vegetables (n=51). Validation studies were conducted with four types of dietary assessment methods within the school lunch setting, all demonstrating moderate accuracy relative to the referent method: weighed plate waste, direct observation, digital photography and self-report instruments. In the studies examining factors related to fruit and vegetable consumption at school lunch, the frequency of methods was as follows: weighed plate waste method (n=21), direct observation (n=14), digital photography methodology (n=12), and self-report (n=4). Most studies utilized cross-sectional (n=15) or quasi-experimental designs (n=24). A socio-ecological framework was used to group 19 environmental factors examined in these studies into 5 clusters of factors: individual, item-specific, meal-specific, cafeteria environment and school-wide/policy. While many factors were explored across studies, relatively few studies accounted for multiple factors in their analyses, leaving room for potential confounding.
Three empirical studies were conducted within a larger, cross-sectional evaluation of FoodCorps, a national farm-to-school program that promotes fruit and vegetable consumption in school-aged children. First, this dissertation conducted a validation study to estimate the accuracy of a self-report questionnaire instrument relative to digital photography for measuring fruit and vegetable consumption in elementary students from 23 schools in a five-phase study. High agreement was observed between student reports of fruit and vegetable items on tray and items observed in digital photographs (match rate ranged from 77 to 88% depending on phase), as well as reports of amounts of fruit and vegetable items consumed (ranges from 67 to 83% depending on phase). There were no differences observed in accuracy of reporting between 2nd and 3rd grade students. It can therefore be concluded that a group-administered self-report instrument can be used to measure fruit and vegetable consumption in a school setting among 2nd and 3rd grade students, providing a potentially less costly instrument than existing objective methods.
Second, a descriptive study reports intra-class correlation estimates for fruit and vegetable outcomes, quantifying the variation in these outcomes attributable to the school-level that can be used in power calculation for future studies. Using 2,571 before- and after-meal digital photographs collected of students’ lunch trays across 40 days of data collection within 20 schools, the intra-class correlation coefficients (ICC) were estimated via multilevel regression models. The observed ICCs for all fruit and vegetable consumption outcomes ranged from 0.159 (vegetables on tray, continuous) to 0.472 (vegetables on tray, binary). Within each of food item category (fruit, vegetables, or fruit and vegetables combined), the highest ICC was observed for items on tray (binary). A multilevel linear model which included as covariates the percent of students eligible for free/reduced price lunch and the percent of white students was shown to decrease the ICC for each fruit and vegetable outcome variable except fruit on tray (binary). The largest for decrease in ICC was for the outcome fruit and vegetables on tray (in cup equivalents), wherein the model reduced ICC from 0.268 to 0.018, a 93% decrease. The power calculations for cluster randomized controlled trial that can conducted using these ICCs will help to ensure that researchers have adequately powered their studies.
Third, select cafeteria environmental factors were examined in a cross-sectional study as they relate to students’ fruit and vegetable consumption at the lunch meal. Using the digital photographs of 2,571 lunch trays from the previous study, the association between fruit and vegetable consumption and several environmental factors was examined. The average consumption of fruit and vegetables was 0.35 cup equivalents (SD=0.31) and 0.24 cup equivalents (SD=0.29), respectively, among students who had them on their tray. When considering students who had a fruit or a vegetable or both on their tray (96% of the sample), the average was 0.45 cup equivalents (SD=0.40). Hierarchical linear models examined environmental variables and fruit and vegetable consumption outcomes: the number of fruit and vegetable items offered (range from 3 to 14 items) was positively associated with vegetable consumption (B=0.021; SE=0.006; P<0.001); noise (rage from 70 DbA to 84 DbA) was negatively associated with fruit consumption (B=-0.012; SE=0.004; P=0.003) and fruit and vegetable consumption (B=-0.017; SE=0.004; P<0.001); recess scheduled before lunch was positively associated with fruit consumption (relative to recess after lunch; B=0.100; SE=0.023; P<0.001) and fruit and vegetable consumption (B=0.096; SE=0.023; P<0.001). Despite cross-sectional evidence of an association, future research is necessary to systematically manipulate these variables to understand their impact.
The results from these three studies and the systematic mapping review are used to develop a conceptual evaluation framework that can be used by researchers to improve the quality and design of studies promoting fruit and vegetable consumption among elementary school-aged children in the U.S.
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More About This Work
- Academic Units
- Behavioral Nutrition
- Thesis Advisors
- Wolf, Randi
- Ph.D., Columbia University
- Published Here
- August 6, 2017