Design and rationale for evaluating salad bars and students' fruit and vegetable consumption: A cluster randomized factorial trial with objective assessments

Abstract

Building healthy fruit and vegetable (FV) consumption habits early in life is critical for primary prevention. However, U.S. youth do not come close to meeting national recommendations for FV intake. School-lunch salad bars are one of the most heavily promoted ways to meet FV guidelines. Contrary to popular belief, no rigorous randomized trials have examined whether salad bars increase students' FV consumption. This paper describes the design and rationale of a federally funded trial to evaluate whether introducing salad bars in elementary, middle, and high schools affects students' FV consumption and waste during lunch. A cluster factorial randomized trial will test new salad bars against waitlist controls, with and without an additional marketing intervention (N = 36 schools, N = 6804 students: n = 12 elementary, n = 12 middle and n = 12 high schools). Objective plate waste measurements of individual student's selection of FVs, consumption, and waste will be conducted using digital scales. Primary aim includes comparing FV consumption in schools without salad bars to those with new salad bars by grade level. Secondary aims include: a) whether FV marketing impacts the success of salad bars for FV consumption; b) whether salad bars differentially result in more FV waste compared to traditional serving methods; c) cost-benefit of using salad bars for consumption over traditional serving methods. When complete, this study stands to be one of the most definitive on the effectiveness of salad bars and contextual factors impacting their success. Findings will provide evidence for how to best spend limited federal dollars to improve FV intake in schools. Trial registration: ClinicalTrials.gov Identifier: NCT03283033 (date of registration: 9/14/2017).

Keywords: Child nutrition; Cluster randomized trial; Fruit; Intervention; School lunch; Vegetables.

Figure 1.

Overview of proposed design, experimental conditions and measurement timepoints.

Figure 2.

Timeline of measurement and intervention activities over the school year.

Figure 3.

Photo of tablets used to assent students using digital scanner to link student IDs to tray/boat barcode IDs.

Figure 4.

Examples of weighed FV items before (top) and after lunch (bottom).