Fostering Sustainable Dietary Habits Through Optimized School Meals - an Intervention Study in Uppsala, Sweden
Phase: NA
Conditions: Food Habits
Sponsor: Karolinska Institutet

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Study protocol with statistical analysis plan 
 
Fostering Sustainable Dietary Habits Through Optimized School Meals 
- an intervention study in Uppsala, Sweden 
Date: January 21, 2020 
 
 
 

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Introduction 
Radical changes to food production and consumption are needed to ensure the attainment of Agenda 
2030 for Sustainable Development and fulfillment of the Paris Agreement (1). Public school meals have 
been highlighted as a suitable setting for children to internalize sustainable dietary habits, which may 
persist throughout life (2). Planning of school meals must take many aspects into account: health 
promotion, environmental impact, acceptability by the consumers and affordability to those paying for 
the meals. Currently many schools use organic products, recycle food packaging and aim to reduce food 
waste, but environmental impacts like greenhouse gas emissions (GHGE) have so far not received much 
attention.  
In Sweden, fully subsidized lunches are served daily in primary schools to all 1.3 million children aged 
6 to 15 (3). Due to their reach and scale (approximately 230 million meals/year at an annual cost of 
around 6 billion SEK), school meals have great potential to increase children’s knowledge about health 
and sustainability, foster sustainable dietary habits and to enable sustainable public procurement.  
This study builds on a previously published strategy for how to optimize, plan and implement 
nutritiously adequate, affordable, acceptable and more climate friendly meals in Swedish primary 
schools (4). In line with this strategy, the present study aims to: a) Apply linear programming to develop 
a GHGE-reduced, nutritionally adequate, and affordable four-week lunch menu plan optimized for 
minimum deviation from the current food supply;  and b) evaluate  the climate impact of the menu, 
effects on food waste, food consumption, and pupils’ satisfaction with school lunches. Our hypothesis 
is that school meals can be optimized to be nutritious and more climate friendly, without negatively 
affecting acceptance, food waste and cost in this context.  
Methods 
Design 
A pre-post design will be used to compare the effect of an optimized menu to the baseline menu on daily 
food waste and consumption at school level. For a baseline period of four weeks children in primary 
schools will receive a baseline menu. After a one-week break (winter break), the optimized four-week 
menu will be served (intervention period).  
 
Recruitment of schools 
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 (4). 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.  
Optimization  
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 (5). 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. 

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Outcomes 
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. Measurements were carried out according to a 
method for measuring food waste and consumption in school restaurants that was based on School Food 
Sweden’s method for measuring school lunch waste and consumption [1]. The method requires 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. The number of plates used daily by the pupils in the school 
restaurant will also be recorded. These measurements will be made daily by the personnel in the school 
kitchens during the baseline as well as during the intervention period. Based on these measurements, the 
total food consumption (kg) will be calculated as the total amount of food prepared in the kitchen (kg) 
minus the total amount of prepared food that is not eaten and has to be thrown away (serving waste in 
kg), the total amount of plate waste (kg), and the total amount of leftover food (kg). Plate waste per 
pupil (g) will be calculated for each day by dividing the total amount of plate waste by the total number 
of plates used. Similarly, the consumption per pupil (g) will calculated for each day by dividing the total 
consumption by the total number of plates used. 
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 grades 5 and 8 will answer the 
questionnaire containing ten questions related to the school lunch. Five of the ten multiple-choice 
questions specifically cover their general (i.e. not for that specific day of week) sense of satisfaction 
with the school lunch. The questions include how often they consider that the school lunch tastes good, 
how many days per week on average they eat it, how often they usually feel full after having eaten lunch, 
and how often they throw away food. They are also asked to provide an overall rating of the school 
lunch. 
Statistical analysis 
A pre-post design will be employed to assess the effect of implementing an optimized lunch menu on 
daily food waste and consumption at school level. Data will be analyzed by interrupted time series 
analysis assessing mean and slope differences in daily food waste and consumption between the two 
periods (6). School lunch satisfaction before and after introduction of the new menu plan will be 
compared by means of Pearson’s X2 test.   

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References 
1. Willett W, Rockstrom J, Loken B, Springmann M, Lang T, Vermeulen S, et al. Food in the 
Anthropocene: the EAT-Lancet Commission on healthy diets from sustainable food systems. Lancet. 
2019;393(10170):447-92. 
 
2. Oostindjer M, Aschemann-Witzel J, Wang Q, Skuland SE, Egelandsdal B, Amdam GV, et al. Are 
school meals a viable and sustainable tool to improve the healthiness and sustainability of children s diet 
and food consumption? A cross-national comparative perspective. Crit Rev Food Sci Nutr. 
2017;57(18):3942-58. 
 
3. The National Food Agency; The Swedish National Agency for Education. Skolmåltiden – en viktig 
del av en bra skola. (The school meal: an important part of a good school: support and inspiration for 
school leaders). Uppsala, Stockholm; 2013. 
 
4. Eustachio Colombo P, Patterson E, Schafer Elinder L, Lindroos AK, Sonesson U, Darmon N, et al. 
Optimizing School Food Supply: Integrating Environmental, Health, Economic, and Cultural 
Dimensions of Diet Sustainability with Linear Programming. Int J Environ Res Public Health. 
2019;16(17). 
 
5. Floren B, Amani P, Davis J. Climate Database Facilitating Climate Smart Meal Planning for the 
Public Sector in Sweden. Int J Food Syst Dyn.8:72–80. 
 
6. Bernal JL, Cummins S, Gasparrini A. Interrupted time series regression for the evaluation of public 
health interventions: a tutorial. Int J Epidemiol. 2017;46(1):348-55.