School meals have considerable potential to shape children's diets and reduce the climate impact of meals. This study applies linear programming for developing and implementing a climate friendly, nutritious and affordable school lunch menu. The new menu plan will be compared to the baseline menu during a 4-week intervention trial. The outcomes will be food waste, consumption, and pupils' satisfaction with the meals before and after introducing the new meal plan analyzed by interrupted time series analysis. Our hypothesis is that school meals can be optimized to be nutritious and more climate friendly, without negatively affecting acceptance, food waste and cost.

Four primary schools in one Swedish municipality with the same menu plan for all schools will participate in the study. Their current meal supply will be recorded in the form of a food list including amount and cost of each item over a 4-week period. This list will then be optimized with linear programming to be as similar as possible to the baseline diet but with a reduction in greenhouse gas emissions of about 30%. No new foods will be introduced and none will be removed from the list. Nutritionally adequacy will be ensured by including constraints into the model. The optimized food list will be handed to the municipality's meal planner and a new menu plan will be developed based on the revised food list. Data on food waste and consumption will be collected daily during a baseline period of four weeks, and during the four-week intervention period. School lunch satisfaction will be assessed twice with an online questionnaire at baseline and during the intervention.

For a period of four weeks, during the spring term of 2020, children from four primary schools in Uppsala municipality will receive a new school lunch menu plan which has been optimized through linear programming to be as similar as possible to the baseline menu while having about 30% lower greenhouse gas emissions (GHGE), being nutritionally adequate, and not more expensive.

During the fall of 2019, a meeting was held with the public meal administration in the municipality of Uppsala. The research team described the OPTIMAT project, including the previously developed strategy for optimizing and implementing more climate friendly lunches in schools. Following this meeting, the municipality agreed to take part in the project. The municipality's meal planner proposed four primary schools for the study, presently having the highest food related GHGE in public meals in the municipality. To be eligible, the intervention schools were required to have on-site kitchens as well as being able to provide electronic recipes for a standard four-week menu. All proposed schools fulfilled these criteria and approved participation.

Recipes for an original (baseline) four-week school lunch menu plan previously served at the recruited schools were obtained through the municipality's electronic meal planning system. The foods included and amounts are considered as the baseline food supply. Each food item included has a code that can be coupled to the Swedish national food database and a national climate database for foods containing life cycle data for each food item. This baseline food supply will be optimized using linear programming. The optimized food list, not including new foods or excluding any foods from the baseline list, will be handed to the municipality's meal planner who develops a new menu plan for the intervention using all foods on the optimized list.

To assess the effect of the new menu plan, data on food waste and consumption will be collected daily in each intervention school four weeks before (baseline) as well as during the four-week intervention with a one-week brake between measurement periods. Kitchen staff will perform daily weighting (using school kitchen scales) of all food prepared in the kitchen (prepared food); the share of the prepared food that is not eaten and has to be thrown away (serving waste); the share that can be saved (leftover food); and plate waste. Total plate waste, plate waste per pupil, serving waste, total consumption, and consumption per pupil will be considered as the primary outcomes as they are regarded as directly related to the pupils' acceptability of the new menu. Data on school meal satisfaction will also be collected through an anonymous online questionnaire at baseline and during the last week of the intervention period. Pupils in grade 8 will answer the questionnaire containing ten questions related to the school lunch.

Inclusion Criteria:

Primary schools (children between 6-16 years in school years 0-9)

• The schools needed to have on-site kitchens
• The schools needed to be able to provide previously used recipes for a standard four-week menu electronically

Exclusion Criteria:

Preschools or gymnasiums

• Schools receiving catered food
• Schools that could not provide recipes electronically