Sustainable and acceptable school meals through optimization analysis: an intervention study

Abstract

Background: School meals hold considerable potential to shape children's diets and reduce food-related greenhouse gas emissions (GHGE)-in the short and long term. This study applied linear optimization to develop a GHGE-reduced, nutritionally adequate, and affordable school lunch menu. The effects on food waste, consumption and pupils' satisfaction with the meals were evaluated.

Methods: A pre-post design was employed to assess the effects of implementing an optimized lunch menu on daily food waste, consumption, and pupils' school meal satisfaction in three schools (grades 0-9) from one Swedish municipality. A food list containing amounts, prices, nutrient content, and GHGE-values of all foods used for a previously served (baseline) four-week lunch menu was created. Using linear programming, this food list was optimized for minimum deviation and constrained to ensure nutritional adequacy and a reduced climate impact. The optimized food list was developed into a new (intervention) four-week lunch menu by a professional meal planner, following the baseline menu as closely as possible. The baseline and intervention menus were served for four weeks, respectively, with a two week break in between. Prepared, wasted and leftover food were weighed daily by the school kitchen staff during both periods. Interrupted time series analysis assessed mean and slope differences in daily food waste and consumption between the two periods. School lunch satisfaction was assessed with an online questionnaire at baseline and during the intervention.

Results: Optimization resulted in a food list that was 40% lower in GHGE, met all nutrient recommendations for school meals, and cost 11% less compared to baseline. The intervention menu was served as planned, with only minor changes required (for practical reasons). Plate waste, serving waste, consumption and school lunch satisfaction did not differ significantly from baseline, in any of the schools.

Conclusions: The findings demonstrate that school meals can successfully be improved regarding health and environmental sustainability using linear optimization, without negative effects on food waste, consumption or cost. This approach offers the necessary flexibility to tailor menus towards different priorities and could therefore be transferred to other types of meal services.

Trial registration: The trial is registered at clinicaltrials.gov (NCT04168632 Fostering Healthy and Sustainable Diets Through School Meals (OPTIMAT).

Keywords: Agenda 2030; Children; Public meals; Sustainable diets.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Food group quantities (g/pupil/day) before (dark blue columns) and after (light blue columns) optimization. The green part indicates the amount increased by the linear programming algorithm; The red parts indicate the amount that was removed from a food group but replaced by other foods of the same food group

Fig. 2

Scatterplots based on ITS analysis displaying plate waste per pupil and consumption per pupil in School 2 as an example. Panel a represents the daily amount of plate waste per pupil during the baseline period (measurement day 0–20, graphs to the left), and the intervention period (measurement day 21–40, graphs to the right); Panel b represents the daily consumption per pupil during the baseline period (measurement day 0–20, graphs to the left), and the intervention period (measurement day 21–40, graphs to the right); Vertical line represents the first day of serving the new menu; P ≥ 0.05 for parameter estimates (β1 and β2) from the ITS analysis