Assessing nutritional compliance, plate waste and menu acceptability in Spanish school meal programmes (ANPAS-Sp): protocol for an explanatory sequential mixed methods study

Abstract

The implementation of healthy, sustainable school menus represents a critical transition requiring strategic management to ensure nutritional compliance, student acceptability, and minimal food waste. Currently, evidence remains inconsistent due to a lack of validated protocols correlating nutritional standards with objective consumption data.

Consequently, a comprehensive, explanatory sequential mixed-methods protocol is developed (ANPAS-Sp). It integrates a systematic nutritional audit (Phase 1) —aligned with Spain’s Real Decreto 315/2025 and Catalonia’s School Menu Review Programme—with high-precision direct weighing of plate waste and validated facial hedonic scales (Phase 2). Furthermore, the protocol employs targeted focus groups to qualitatively explore food rejection patterns identified after quantitative phase (Phase 3).

This protocol facilitates evidence-based interventions and data pooling to advance sustainable school food systems. It spearheads a standardized evaluation framework for public health policies, establishing a new benchmark for gathering integrated evidence. Ultimately, this approach provides the necessary tools to transform school meal programs into healthy, widely-accepted, and zero-waste systems.

• •Approach: A standardised evaluation framework that empirically correlates the compliance of nutritional recommendations, the quantification of plate waste, and student acceptability of school meals.
• •Impact: It provides the necessary scientific tools to optimise school meal programmes and promote the transition towards sustainable school food systems.

Graphical abstract

Specifications table

Subject area	Medicine and Dentistry
More specific subject area	Public Health; Nutritional Science; School meal programme evaluation; Plate waste audit methodology; Menu acceptability; Protocol for an explanatory sequential mixed methods study; Pediatric Nutrition, and Sustainable Food Systems.
Name of your protocol	Assessing Nutritional Compliance, Plate Waste and Menu Acceptability in Spanish School Meal Programmes (ANPAS-Sp): Protocol for an Explanatory Sequential Mixed Methods Study.
Reagents/tools	Calibrated precision scales (±0.1 g); DIAL dietary assessment software version 3.15; SPSS statistical software version 29; MAXQDA qualitative analysis software version 26; 5-point facial hedonic scale.
Experimental design	Explanatory Sequential Mixed-Methods Design. Includes assessment of the compliance of the school menu, direct weighing of plate waste and acceptability scoring (facial hedonic scale) in schools, followed by focus groups with the educational community
Trial registration	Not applicable
Ethics	The study was approved by the Ethics Committee of the Universitat Oberta de Catalunya (UOC) with the Reference CE24-PF35 + CE25-PR22.
	All procedures involving human participants were performed in accordance with the ethical standards of the 1964 Helsinki Declaration and its later amendments. Written informed consent was obtained from all participants (parents/legal guardians and school staff).
Value of the Protocol	•Methodological integration for holistic diagnosis: This mixed-methods protocol sequentially integrates nutritional compliance (documentary phase), objective quantification of plate waste via direct weighing, and subjective student acceptability (hedonic scales). This integration allows not only for measuring the magnitude of food rejection but also for empirically and statistically correlating waste volume and students’ subjective acceptance.
	•Assessment of sustainability policy impact: The design is specifically aligned with new legislative frameworks: Spanish Law 1/2025 on food waste and Real Decreto 315/2025 and Barcelona’s intervention programmes like MEMSS (Healthier and More Sustainable School Meals programme). It provides a validated tool to monitor the transition toward school menus with higher plant-based protein content, evaluating their actual feasibility within the educational environment.
	•Qualitative exploration of rejection determinants: By including focus groups with multiple stakeholders (school teachers, families, kitchen staff, and school lunch supervisors), the protocol enables an in-depth exploration of the perceptual and contextual drivers behind the quantitative data.

Background

Schools serve as strategic settings for the promotion of healthy and sustainable dietary habits. This transition is currently driven by public policies, such as Spain’s Real Decreto 315/2025 (RD 315/2025) [1], which promotes balanced and environmentally friendly nutrition in schools. However, if such transition is not accompanied by strategies to ensure acceptance, it may lead to an increase in food waste, a problem with major nutritional, economic, and environmental implications.

Plate waste (PW) is defined as the amount of food served that is not consumed [2] It accounts for 20% to 29% of the food prepared in school canteens, equivalent to 32 to 130 g per student [[3], [4], [5]] PW in school canteens poses public health challenges across nutritional adequacy, economic efficiency, and environmental sustainability by undermining the benefits of balanced school meal programmes [6,7] According to studies conducted by the Food and Agriculture Organisation of the United Nations (FAO), global food waste (FW) costs USD 2.6 trillion annually and represents between 8% and 10% of global greenhouse gas emissions [4]

The measurement of PW serves as an indirect method to analyse acceptability, influenced by preferences, habits, and social context [[8], [9], [10]]. Objective quantification methods include visual estimation, double weighing, and pre–post consumption photographic records; while subjective acceptability is measured through questionnaires, interviews, and hedonic scales [11]

Despite growing interest in mitigating this issue—in line with the Sustainable Development Goals (SDGs) within the United Nations 2030 Agenda [3], the EU Farm to Fork Strategy [12], the Barcelona Healthy and Sustainable Food Strategy 2030 [13], and the Milan Urban Food Policy Pact Global Forum 2025 Final Declaration [14]—there remains a lack of scientific protocols linking healthy and sustainable school menus with direct effects on waste and acceptability.

This protocol is notable for its innovative approach in analysing the nutritional quality of school menus based on Spain’s RD 315/2025 [1] and Barcelona’s MEMSS programme (Menjadors Escolars Més Sans i Sostenibles - Healthier and More Sustainable School Meals programme) [15], which is based on PReME (School Menu Review Programme in Catalonia) [16]; the analysis of PW using the double weighing technique, considered one of the most quantifiable methods, ensuring international comparability [11,17]; and the analysis of acceptability through the facial hedonic scale, a method validated by recent systematic reviews for its low cost, simplicity, rapid application, and ease of understanding [11]

By integrating objective and subjective measurements, this protocol aims to generate evidence-based data. Scientifically, it provides insights into the relationship between sustainability, nutrition, and behaviour. Socially, it optimises school feeding and collective catering programmes. Environmentally, it contributes to the reduction of food waste and the advancement of the SDGs.

The general objective of the study described in this protocol is to jointly evaluate nutritional compliance, PW, and menu acceptability in educational centres participating in the MEMSS programme in Barcelona [15], analysing the association between these three elements.

Description of protocol

Rationale

PW in school canteens is a multifaceted challenge driven by factors such as menu composition, culinary preparation, and, crucially, student acceptance. In Spain, the evaluation of school catering has a strong foundation in the School Menu Review Programme, PReME, in Catalonia, which has long provided a framework for monitoring dietary compliance and nutritional compliance [18] However, while programmes like PReME have successfully standardised the documentary review of menus, there is a critical need to evolve towards methodologies that reflect actual consumption.

Currently, schools in Barcelona—particularly those within the MEMSS programme [15]—are undergoing a strategic transition toward healthier and more sustainable menus by prioritizing plant-based proteins and fresh, seasonal products. While this shift is essential for promoting sustainable diets and complying with RD 315/2025 [1], it carries a risk of increasing FW if the new offering is not well-received by students [19]

The core rationale for this protocol lies in the current scarcity of validated methodologies that empirically link the transition to healthy and sustainable school menus with their direct impact on student acceptability and the resulting volume of PW. To address this gap, this protocol introduces a rigorous, replicable, mixed-methods procedure that aims to evaluate the association between three high-standard pillars: the compliance of school menus, the volume of PW and the level of menu acceptability.

By triangulating these quantitative and qualitative data, the protocol provides a holistic understanding of the relationship between sustainability, nutrition, and behaviour. Crucially, this methodology supports evidence-based public policy, enabling school meal programmes to reduce PW without compromising healthy and sustainable-nutritional compliance. These results are vital for optimising school meal programmes (such as the MEMSS initiative), providing practical recommendations to the collective catering sector, and generating public policies that contribute to the SDGs through a more efficient and socially accepted school food system.

Experimental design

This study will employ an explanatory sequential mixed methods design, adhering to the GRAMMS (Good Reporting of A Mixed Methods Study) [20] guidelines to ensure transparency in the reporting of the study methods and findings. In this study, the qualitative findings will help interpret the statistical results emerging from the quantitative phase, offering potential validation for the outcomes (Fig. 1). The research will be conducted within the framework of the MEMSS programme [15]. This strategic initiative, supported by the Barcelona City Council and the Barcelona Public Health Agency (ASPB), aims to transform school canteen menus by fostering nutritionally balanced and environmentally sustainable eating patterns, focusing on reducing animal protein, increasing plant-based protein, and prioritizing fresh, local products [15]

Fig. 1.

Explanatory sequential mixed methods diagram.

The study population will consist of schools participating in the MEMSS intervention. This includes a total of 12 schools from diverse socioeconomic districts of Barcelona, Spain, which, after receiving the project information, voluntarily choose to participate in the programme. This involves a multi-stakeholder group of students, school management, kitchen and catering staff, school lunch supervisors, and families.

The research will be structured into three integrated chronological phases:

• −Phase 1: Nutritional analysis of menu compliance. A systematic documentary review of a full monthly cycle of school menus will be performed to assess their compliance, using a standardised checklist based on the nutritional frequency requirements and sustainability criteria established by RD 315/2025 legal frameworks and the specific MEMSS programme guidelines. This phase will establish the baseline of “what is offered” versus “what is regulated”.
• −Phase 2: PW and acceptability assessment. Quantitative data will be collected during a one-week intensive observation period per school. PW will be quantified using the direct weighing method of the total amount of each menu course. Menu acceptability will be measured using a 5-point validated facial hedonic scale. This quantitative phase adheres to the STROBE statement (Strengthening the Reporting of Observational Studies in Epidemiology) to report observational data.
• −Phase 3: Qualitative explanatory exploration. Using the prior quantitative results, focus group discussions (FGDs) will be conducted to explore the underlying perceptions and reasons for food rejection. A purposive sampling strategy will be used to recruit participants (kitchen staff, school lunch supervisors, school teachers and families). This qualitative phase adheres to the SRQR (Standards for Reporting Qualitative Research) guidelines to ensure the appropriate reporting of the study methods and findings [21,22]

Following an explanatory sequential logic approach, the design will first establish the statistical associations between menu nutritional compliance, PW, and acceptability. These quantitative findings will then inform the subsequent qualitative component, ensuring that it effectively explores the contextual and perceptual factors for food rejection and provides a holistic evaluation of the transition toward more sustainable school menus.

Reagents and tools

Table 1 summarizes the tools employed in this protocol, detailing their purposes and sources for reproducibility.

Table 1.

Protocol tools, purposes, and details.

Tool/Reagent	Purpose	Details/Source
Pre-established data templates	Data management	Standardised menu assessment instrument (Supplementary file 2), plate waste recording instrument (Supplementary file 3) and acceptability recording instrument (Supplementary file 5).
1. Menu assessment
2. Plate waste recording
3. Acceptability recording
Calibrated precision scales - Mettler Toledo MT 8001 Precision Balance (version 1504) (±0.1 g)	Quantification of plate waste (direct weight)	Provides high precision ensuring objective and reproducible measurement.
5-level facial hedonic scale	Measurement of student menu acceptability	Validated instrument for acceptability assessment in primary school children (face-to-face administration) (Supplementary File 4).
DIAL software version 3.15	Estimation of nutritional and energy losses	Used to calculate energy (kcal), macronutrient, and micronutrient losses.
SPSS software version 29	Statistical analysis	Used for descriptive and association analysis including statistical significance and effect sizes.
MAXQDA software version 26	Qualitative data analysis	Used for framework analysis of focus group discussion.

Step-by-Step protocol

To achieve the overarching goal of evaluating menu nutritional compliance, PW, and menu acceptability in schools participating in the MEMSS programme [15], and to analyse the relationship between these three elements, a series of specific objectives are proposed, organised into three distinct phases. The protocol follows a chronological structure, detailing each procedural step to ensure reproducibility.

All the phases, along with their respective timelines, are included in Supplementary File 1 (Schedule of enrollment, interventions, and assessments).

Table 2 summarizes the study phases, their specific objectives, and the key procedural steps for reproducibility.

Table 2.

Study phases, specific objectives, and key procedural steps.

Study Phase	Specific Objective	Key Procedural Steps
Phase 1: Data collection and nutritional compliance assessment (Contextualization)	To evaluate the alignment of the offered school menus with the MEMSS programme guidelines and the current legislative framework.	1. Systematic collection of baseline school menus from two representative periods (November 2025 and May 2026) for each participating centre to account for seasonal dietary variations in food procurement and consumption.
		2. Standardised documentary audit: multi-level audit using a validated checklist based on the MEMSS programme guidelines[16] and the Spanish legislative framework RD 315/2025[1], to assess menu compliance.
		3. Quantitative calculation of compliance levels regarding food group consumption frequencies, comparing observed patterns against established guidelines (Composite Compliance Score).
Phase 2: Plate waste quantification, Nutritional value estimation and Acceptability assessment	To quantify plate waste (PW) and identify critical food items with high rejection rates.	1. Baseline Portion Characterisation: establish reference portion sizes by weighing representative samples of each menu component (first course, second course, side dish, bread and dessert) prior to service.
		2. Direct PW quantification: measure edible waste using calibrated precision scales (±0.1 g) over a five-day audit per school, ensuring component-wise segregation.
		3. Calculation of performance indicators: Total Grams Wasted (TGD), Mean Grams Discarded per User (MGDU), and Plate Waste Index (PWI).
	To estimate the nutritional and energetic value lost due to plate waste.	1. Use the DIAL dietary evaluation software to calculate the loss of energy (kcal), macronutrients, and micronutrients associated with the recorded waste.
	To assess students’ acceptability of school menus using validated tools.	1. Concurrent acceptability assessment through daily administration of a 5-level facial hedonic scale.
		2. Calculation of the Acceptability Percentage (AP), defined as the proportion of students rating the dish in the two highest categories of the scale.
	To establish the statistical association between plate waste and subjective student satisfaction.	1. Association and stratified analysis using bivariate correlations and regression models in SPSS software to determine the effect size of the relationship between PWI and AP.
Phase 3: Focus Group Discussion	To examine qualitatively food rejection patterns through an interpretative exploration of stakeholder perceptions related to nutritional compliance, generated waste and menu acceptability.	1. Purposive sampling to recruit a multi-stakeholder group (kitchen staff, school lunch supervisors, families, management) to capture diverse perspectives in the canteen service.
		2. Conduct of Focus Group Discussions using a semi-structured guide informed by the quantitative results.
		3. Verbatim transcription of audio recordings and performance Framework Analysis using MAXQDA software.
Data reporting and methodological rigor	To guarantee transparency, reproducibility, and integrative quality by adhering to international evidenced-based reporting standards for mixed methods research.	1. Quantitative reporting: Apply the STROBE statement (Strengthening the Reporting of Observational Studies in Epidemiology) to report observational data.
		2. Qualitative reporting: Adhere to the 14 categories of SRQR guidelines (Standards for Reporting Qualitative Research) to ensure a clear description of the methodological rationale and its connection to existing knowledge.
		3. Mixed methods reporting: Follow the GRAMMS guidelines to document the mixed methods design and findings.
Outcome, impact and application	To derive evidence-based interventions and actionable policy recommendations aimed at optimising menu nutritional quality, enhancing student acceptability and satisfaction, and mitigating plate waste in school catering systems.	1. Formulation of actionable guidelines for educational institutions and the institutional catering sector by integrating quantitative indicators (menu nutritional compliance, plate waste metrics, and hedonic scores) with qualitative insights into the underlying drivers of food rejection.

Phase 1: Data collection and nutritional compliance assessment (contextualization).

This initial phase aims to evaluate the compliance of the offered school menus within the MEMSS programme guidelines with the current dietary legislative framework.

The study population will focus on schools (out of a total of 12) that have completed the full evaluation in the MEMSS programme and that decide to participate voluntarily in the study. In these participating schools, a systematic documentary audit will be conducted to assess both the nutritional quality and regulatory compliance of the provided menus.

Step 1.1. menu documentation collection

Participating schools will be contacted, through formal electronic communication, and requested to provide their complete baseline menus. To ensure a representative characterisation of dietary patterns and seasonal food availability, menus will be collected from each participating centre for two distinct representative periods: Autumn-Winter (November 2025) and Spring-Summer (May 2026). Special or medical diets (e.g., allergies, intolerances) will be excluded from this analysis to ensure a standardised comparator.

The unit of analysis will be the "monthly menu cycle," defined as 20 consecutive school days.

Step 1.2. systematic audit and compliance assessment

Menu adherence to nutritional and sustainability guidelines will be assessed through a standardised independent peer-review process. Two trained researchers independently will evaluate the collected menus using a customized audit instrument. This tool integrates the PReME framework [18] and the mandatory requirements of Spain’s RD 315/2025 [1], although enacted in April 2025, this decree is scheduled to officially enter into force in April 2026, establishing a new mandatory regulatory baseline that coincides with the study's data collection and evaluation period. All extracted menu data will be recorded in pre-established templates, following standardised data entry guidelines to ensure replicability (Supplementary File 2).

The evaluation will be operationalized through three specific analytical layers:

• −Frequency thresholds: evaluators will record the weekly and monthly distribution of food groups (e.g., legumes, fish, meat) categorized by dish type (first course, second course, side dish, dessert and bread). This analysis will be performed using the "Weekly and monthly distribution of different food groups" table for each of the four weeks of the cycle, and the data is consolidated into a monthly total to assess long-term balance. Subsequently, all recorded consumption frequencies will be transferred to a comparative compliance matrix, using the "Results and recommended frequencies comparison" table. This matrix contrasts the observed frequencies with the "gold standard" ranges defined by the PReME and Spanish national legislation (RD 315/2025).
• −Culinary techniques and processing level: menus will be screened for cooking techniques (e.g., frying vs. baking), the presence of ultra-processed products, sugary beverages, and specific information regarding the type of oils used for dressing and cooking; by following the "additional aspects to consider" table, compliance with additional items related to culinary techniques and sustainability is evaluated.
• −Sustainability-related metrics: inclusion rates of seasonal products, organic ingredients, and locally sourced products will be quantified based on the information provided in the menu descriptions.

To ensure inter-rater reliability, any discrepancies in the independent evaluations will be resolved by a third senior expert. The final output of Phase 1 will be a "compliance score" for each school, which serves as the independent variable for the explanatory analysis in Phase 3.

Step 1.3. calculation of compliance indicator

To transform the audit data into quantifiable variables for statistical analysis, two primary metrics will be calculated for each school menu cycle (20 days):

• −Composite Compliance Score (CCS) calculated as (Number of criteria met / Total number of criteria evaluated) × 100.

This indicator measures compliance with the guidelines. Due to the coexistence of local (PReME) and national (RD 315/2025) frameworks, and considering the different number of items evaluated in each (PReME = 106, RD = 95), the compliance assessment is divided as follows:

• −CCS PReME: (Number of PReME criteria met / 85) x 100.
• −CCS RD: (Number of RD criteria met / 75) x 100.

Each criterion will be treated as a dichotomous variable (1 = Compliant; 0 = Non-compliant). Discrepancies between the two regulations (e.g., more stringent plant-protein frequencies in PReME) will be documented separately to identify specific areas of regulatory friction.

To ensure a standardised and evidence-based interpretation of the findings, the CCS Index results will be classified into three levels, aligned with the official inspection criteria established in the 'Protocol of Minimum Criteria for the Evaluation of Food Offering in Educational Centres' by the Spanish Agency for Food Safety and Nutrition (AESAN) [23]:

• −Compliance (100%): The menu is fully consistent with the frequency ranges defined by PReME and RD 315/2025. No deviations, representing the optimal nutritional target.
• −Acceptable Alignment (75% - 100%): This level requires specific corrective recommendations to address minor deviations and reach full alignment with nutritional targets.
• −Non-Conformity (< 75%): This level indicates a significant divergence from the regulatory framework, where the nutritional quality of the offering is compromised and mandatory corrective actions are required.

Phase 2: Plate waste quantification, Nutritional value estimation and Acceptability assessment.

This phase will employ a cross-sectional design conducted concurrently over an entire school week (Monday through Friday) at each participating site. To ensure data reliability and minimize bias, two trained researchers will be present throughout the meal service to perform direct weighing of plate waste to assess menu acceptability. This concurrent data collection strategy is specifically designed to allow the subsequent correlation of objective PW metrics with subjective student satisfaction, providing a comprehensive view of the school canteen’s performance and the nutritional impact of the generated waste. All plate waste data will be recorded in pre-established templates (Supplementary File 3).

Step 2.1. plate waste quantification

Step 2.1.1. Portion characterisation and baseline weighing. Prior to the start of the meal service and the audit, three random complete meal samples will be weighed to establish the average reference weight of the served portion for each meal component (first course, second course, side dish, bread, dessert). This average will serve as the “standard served portion” used to calculate the percentage of waste in the subsequent analysis.

Step 2.1.2. Monitoring planning precision. For every data collection day, both planned and actual diner counts will be recorded per menu type. This includes a breakdown of standard meals versus special dietary requests, such as those for allergies, intolerances, or religious beliefs. All data will be entered into a standardised template to calculate planning precision indicators, specifically the absolute difference and the percentage deviation between planned and served meals.

Step 2.1.3. Waste separation protocol. The collection area will be organized with separate containers for each dish category (first course, second course, side dish, bread, dessert). During tray clearing, it is crucial to collect only the edible portion of the leftovers. Non-edible components, such as seeds, and bones, must be excluded to prevent overestimating PW [24]

Step 2.1.4. Direct weighing of plate waste . When the meal service finishes, the total accumulated waste for each dish category will be weighed using calibrated digital precision scales (±0.1 g).

• 1. Place the specific waste container on the scale.

• 2. Tare the scale to exclude the container’s weight.

• 3. Record the net weight of the edible waste (in grams) in the data log, ensuring traceability by linking each entry to the specific date, school site, and dish type [25,26]

Step 2.1.5. Calculation of standardised waste indicators. Using the recorded weights and headcounts data, the following metrics will be computed to allow for inter-school comparison:

• −Total Grams Discarded (TGD): The aggregate weight of all edible residues generated during the service.
• −Mean Grams Discarded per User (MGDU): Total edible residues (g) / Total number of diners evaluated.
• −Plate Waste Index (PWI): Expressed as a percentage to indicate the proportion of the served meal that was rejected: (Weight of edible residue / Mean weight of served edible portion) × 100.
• −Rejection Ranking: Identify the “most rejected food types” by rank-ordering across all dish categories.

Step 2.2. nutritional value estimation

Once the field records (served portions, PW by dish type, headcount and planning indicators) have been validated, the nutritional impact of the waste will be quantified to determine the gap between the nutrients served and those actually consumed [27]

Step 2.2.1. Software configuration and data input. The DIAL dietary assessment software version 3.15 will be used to model the recipes served during the audit school week [28] Each recipe will be standardised in the software, reflecting the ingredients and quantities used by the catering service.

Step 2.2.2. Estimation of nutritional loss. The net weight of the PW, recorded in Step 2.1.4, will be cross-referenced with the nutritional composition of the corresponding recipe. For each menu component and data collection day, the energy (kcal), macronutrient (protein, carbohydrate, lipid), and micronutrient (e.g., fiber, iron, calcium, vitamin A) content of the discarded portion will be calculated.

Step 2.2.3. Data aggregation and inefficiency analysis. To identify key patterns, results will be summarized at three distinct levels:

• −Dish type: Identifying which specific menu components contribute most to nutritional loss.
• −Daily level: Assessing the total nutritional impact for each day of the school week.
• −Aggregate (global) level: Calculating the "Nutritional Inefficiency Ratio," defined as the percentage of served nutrients that remain unconsumed by students.

Step 2.3. acceptability assessment

This step involves evaluating student’s subjective perceptions of the menu to identify the qualitative drivers influencing the plate waste measured in previous steps.

Step 2.3.1. On-site data collection and sampling. Alongside the PW audit, menu acceptability among students will be assessed. A cluster sampling approach (by school) will be used, targeting a sample of 50–70 students per dish per school (ensuring a minimum of 30 valid responses per dish for statistical significance).

• −Instrument: A 5-point facial hedonic scale, ranging from "I really dislike it" to "I really like it," will be used. This validated visual tool is designed to minimize cognitive burden and overcome potential literacy barriers among younger children (Supplementary File 4).
• −Administration: Two trained researchers will be stationed in the canteen area. As students finish their meals, they will be asked to rate each component (the first course, second course, side dish, bread, and dessert).
• −Data logging: Individual ratings will be recorded using a standardized template, ensuring each entry is linked to the specific day, school, dish type, and class group (Supplementary File 5).
• −Quality control: Prior to analysis, all records will be audited for completeness and consistency; incomplete surveys or those with ambiguous markings will be excluded.

Step 2.3.2. Acceptability indicator and stratification. Once the database is validated, the following analytical procedures will be implemented:

• −Sample characterisation: A detailed description of the participating student population will be provided, including total sample size, distribution by school site, sex (male/female/other) and educational stage.
• −Acceptability Percentage (AP): This is the primary measure. It is defined as the proportion of students who rate the dish within the two highest categories of the scale (“like” and “like very much”).
• −AP= [n (positive ratings) / N (total valid responses)] x 100.
• −Comparative and stratified analysis: to identify specific patterns of preference and potential disparities. Results will be compared using inferential statistics, performed across school sites, educational stage (grade level), and sex.
• −Data integration: These results will be formatted for subsequent bivariate correlation with the Plate Waste Index (PWI) in the statistical analysis phase.

Phase 3: Focus Group Discussion.

This phase will adopt an interpretative, naturalistic approach to explore the reasons behind the quantitative patterns identified in Phases 1 and 2. SRQR (Standards for Reporting Qualitative Research) guidelines [18,19], will be followed to ensure transparency in the reporting of the study methods and findings.

Step 3.1. Purposive sampling and ethical procedures. Participants will be selected through purposive sampling to ensure maximum variation and representation of the school community. The study will engage a diverse range of key stakeholders, including kitchen staff, school lunch supervisors, school management, and families. The recruitment process will commence with the distribution of formal invitations through established school communication channels. Participants will provide written informed consent. To ensure reflexivity, researchers’ characteristics and potential biases will be documented prior to engagement.

Step 3.2. Focus Group Discussion implementation. An Integrated Approach. The qualitative phase is designed to provide context to the previously collected quantitative metrics. At least one FGD will be conducted per school site, with sessions lasting between 60 and 90 min to ensure sufficient time for thematic exploration.

To guarantee methodological rigour, sessions will be led by a trained moderator following a semi-structured guide designed to encourage open dialogue while maintaining focus on the research objectives. Simultaneously, a co-moderator will be responsible for documenting non-verbal cues, group dynamics, and relevant contextual observations that may influence the data.

The discussion guide will be structured to explore several key dimensions. Initially, participants will share their perceptions of the current menu and reflect upon the PW data generated in the previous phase. The dialogue will then pivot to identifying the primary drivers of food rejection, specifically focusing on organoleptic properties.

Furthermore, the sessions will examine broader contextual factors, including the physical dining environment, levels of supervision, time constraints, and meal presentation. The FGD will conclude by identifying and evaluating feasible interventions aimed at waste reduction and optimisation of the overall school meal experience.

Integration at the data collection stage will be achieved by using the quantitative findings from Phases 1 and 2 to directly inform the content of the FGD semi-structured guide (Fig. 1). This will ensure that the qualitative strand focuses on explaining the quantitative findings, including potential unexpected results or discordant patterns identified in the previous stages.

To link the specific quantitative results with the qualitative inquiry, a two-column interview prompt joint display will be created, featuring the key quantitative outcomes in the first column and the corresponding qualitative questions in the second. During this process, the research team will analyse the quantitative dataset to identify specific ‘deductive anchors’ that will serve as the foundation for the discussion. The guide will be structured around the following integration criteria:

• −Investigating nutritional-perceptual friction: Drawing on Phase 1 CCS results, the FGDs will specifically target menus that meet high nutritional and sustainability standards but exhibit poor student acceptance, aiming to identify culinary or contextual barriers to healthy eating.
• −Explaining high-waste/low-acceptability patterns: For dishes identified in Phase 2 with a high PWI or low AP, specific questions will be formulated to explore sensory drivers—such as taste, texture, or appearance—that numerical data alone cannot capture.
• −Probing subgroup disparities: Should the quantitative analysis reveal significant variances in waste or satisfaction based on grade level, sex, or SES, the FGD questions will be tailored to explore the unique contextual factors underlying those specific groups or school environments.
• −Clarifying discordance: In cases where objective PW metrics conflict with subjective student ratings (e.g., high reported liking despite high waste percentages), the FGD will prioritize uncovering ‘alternative explanations’ to ensure the credibility of the subsequent meta-inferences.

Step 3.3. Data management and transcription. All sessions will be audio-recorded with prior participant’s consent. All personal identifiers will be anonymized. Transcribed verbatim will be recorded and the final transcription will be imported into MAXQDA software version 26 for systematic data management and analysis.

Data measurement and analysis

The study will employ an explanatory sequential mixed methods design, where both the quantitative and qualitative analyses are carried out independently, subsequently followed by the integration of the inferences generated from both. Quantitative analyses will determine the magnitude and statistical significance of the association between menu nutritional compliance, plate waste and acceptability; while qualitative analyses will elucidate the underlying mechanisms and perceptions that contribute to explain these findings.

• a). Quantitative data analysis.

The data will be processed and analyzed using IBM SPSS Statistics (v.29). To provide a comprehensive overview of the meal service's performance, descriptive statistics will be calculated for all primary indicators—including TGD, MGDU, PWI, and AP—as well as for overall nutritional losses. These results will be reported using means ± SD for normally distributed data, while medians with Interquartile Ranges [IQR] and 95% Confidence Intervals (CI) will be employed for non-parametric distributions.

Regarding inferential analysis, differences in waste and satisfaction levels across groups—stratified by grade level, sex, and school socioeconomic status (SES)—will be assessed using independent t-tests or One-way ANOVA with Bonferroni post-hoc corrections for multiple comparisons. Prior to these analyses, the assumptions of normality and homoscedasticity will be rigorously tested; where these assumptions are violated, the Mann-Whitney U or Kruskal-Wallis tests will be applied as robust non-parametric alternatives.

To explore associations between variables, the relationship between PW volume and menu acceptability will be evaluated through Pearson or Spearman correlation coefficients, depending on the data distribution. Furthermore, hierarchical linear regression modelling (multilevel models) will be employed to account for school-level clustering, ensuring that the nested nature of the data is accurately reflected in the results.

Finally, all reporting will strictly adhere to the STROBE guidelines for observational studies. The interpretation of the findings will prioritise effect sizes (r, β), 95% CIs, and the proportion of variance explained (R²), rather than relying solely on p-values. To guarantee the reproducibility and robustness of the findings, comprehensive model diagnostics, including assessments of multicollinearity and residual homoscedasticity, will be systematically performed throughout the analysis.

• b). Qualitative data analysis.

Qualitative data from the FGD will be analyzed using MAXQDA software, following the Framework Method [29]. The following seven phases will be followed: [1] Transcription of recordings; [2] Familiarization with the interview through repeated reading; [3] Coding the transcripts line-by-line; [4] Developing a working analytical framework by grouping codes into categories; [5] Applying the framework (indexing) to the whole dataset; [6] Charting the summarized data into a matrix; and [7] Interpreting the data.

Methodological trustworthiness and integration

To ensure the trustworthiness of the qualitative component, Lincoln and Guba’s (1985) [30] criteria will be considered. The following strategies will be followed to achieve compliance with each criterion:

• −Credibility: Data will be triangulated by cross-validating narratives against the quantitative results of Phases 1 and 2. To ensure accuracy, we will employ member checking by sharing synthesized summaries with participants during follow-up interviews.
• −Transferability: Transferability will be addressed by providing 'thick, contextualized descriptions' of the school environment and participants. These details allow readers to evaluate the applicability of the findings to comparable educational or catering settings.
• −Dependability: A comprehensive audit trail will be maintained to document all analytical decisions and modifications made to the coding framework throughout the research process.

Final integration and evidence-based recommendations

Following the explanatory sequential design, will integrate the qualitative insights with the quantitative data from previous phases. This synthesis will be used to generate targeted recommendations for policymakers, catering companies and school staff, focusing on enhancing menu satisfaction, reducing waste and achieving an effective transition toward more sustainable food systems.

The integrated interpretation will proceed through a structured three-step process:

• 1. Alignment of Findings: For each of the study's dimensions (nutritional compliance, objective plate waste, and student acceptability), the quantitative results will be systematically aligned side-by-side with the qualitative themes emerging from the focus groups.

• 2. Assessment of Fit: The research team will compare these results to characterize the nature of their relationship, specifically determining instances of convergence (concordance), divergence (discordance), complementarity, or expansion. While all forms of 'fit' will be documented, the analysis will focus primarily on complementarity, as the qualitative narratives are intended to explain, illustrate, and provide depth to the quantitative findings regarding food rejection.

• 3. Generation of Metainferences: As the final output of the comparative analysis, the team will generate metainferences. These are integrated conclusions—expressed as a narrative or theoretical statement—that surpass the sum of the individual quantitative and qualitative inferences, providing a holistic diagnosis of the school canteen environment.

To systematically address possible divergences or contradictory findings between the quantitative and qualitative data, we will employ the mixed methods strategy of 'comprehensive Case and Variable Analysis' [31], as described by Younas et al. (2023). This strategy will involve identifying discordant findings in the quantitative data, identifying supporting evidence in the qualitative data, and selecting variables for mixed analysis and interpretation. Once these divergences are identified, they will be addressed following the strategies provided by Pluye et al. (2009) [32]. We will apply either the reconciliation strategy to examine the origin of the divergence (for example, whether it is due to the instruments used in the study), or the initiation strategy to assess whether the divergence requires a more specific and thorough study in future research.

Reporting standards and methodological rigor

To ensure the highest level of transparency, reproducibility, and methodological quality, the study’s findings will be reported in strict accordance with international evidence-based guidelines. The quantitative components (nutritional compliance and plate waste) will follow the STROBE statement [33], ensuring a comprehensive description of the setting, participants and statistical methods.

The qualitative findings will adhere to the SRQR guidelines. This 21-item checklist is utilized to enhance the clarity of the research design, data collection and thematic analysis [21,22] By adhering to these complementary standards, the protocol will facilitate critical appraisal by the scientific community and minimize research waste, providing a transparent audit trail of the decision-making process throughout the mixed-methods implementation.

Study guidelines and ethical considerations

Human subject guidelines

The study will be conducted in strict accordance with the ethical principles of the Declaration of Helsinki and the Belmont Report, encompassing the core principles of beneficence, autonomy, and justice.

Formal ethical approval for the protocol has been granted by the Ethics Committee of the Universitat Oberta de Catalunya (References CE24-PF35, issued March 19, 2024; and CE25-PR22, issued March 13, 2025).

Furthermore, data processing within the framework of this project will be conducted in full compliance with national and European data protection regulations (GDPR), as confirmed by the official report issued by the Data Protection Officer on November 25, 2025.

Informed consent and assent will be mandatory for all adult participants, including school staff, catering personnel, school lunch supervisors, and families. For participating minors, recruitment is conditional upon receiving prior written consent from a parent or legal guardian, as well as the child’s own assent, which will be obtained using age-appropriate and visually accessible materials. All consent documents will explicitly detail the study objectives, procedures, and data handling protocols, alongside potential risks and benefits. Furthermore, these documents will clearly state the participant’s right to withdraw at any stage of the study without any academic or service-related repercussions.

All personal data will be managed with strict confidentiality in full adherence to current data protection regulations. To ensure participant anonymity, all identifiable information will be stored separately from research datasets, and analysis files will be pseudonymized using unique alphanumeric codes. Access to raw, identifiable data is strictly restricted to authorized members of the research team. Furthermore, all datasets will be securely stored for five years following publication, after which they will be destroyed in accordance with institutional security protocols.

The study is designed to maximize potential benefits—such as improving the nutritional quality and sustainability of school meals—while minimizing potential risks, which are expected to be low. Specific measures have been implemented to protect vulnerable populations, particularly minors; these include using age-appropriate communication and ensuring the presence of familiar school staff during data collection to prevent any discomfort. Furthermore, a continuous risk–benefit assessment will be maintained throughout the project. Any concerns or issues raised during the focus group discussions will be addressed immediately by the research team to ensure ongoing participant safety and well-being.

Key findings and evidence-based recommendations will be shared with participating schools and families through accessible executive summaries. This dissemination strategy ensures that the study's results contribute directly to the improvement of the local educational community while strictly maintaining individual confidentiality. By providing these tailored reports, the research team aims to translate data into actionable insights for school administrators and parents alike.

Study guidelines

The methodology incorporates standardised guidelines to enhance reproducibility and facilitate international comparison. The nutritional and dietary compliance of the school menus is evaluated using a protocol based on the PReME programme [18] of Catalonia, adapted for scientific rigor through a co-design process involving researchers from the Universitat Oberta de Catalunya (UOC) and experts from the Public Health Agency of Barcelona (ASPB). This collaborative validation ensures that the evaluation tools are both institutionally aligned and methodologically robust for assessing adherence to current healthy and sustainable dietary guidelines.

The waste audit procedures for segregating and measuring student PW are aligned with the 'Guide to Conducting Student Food Waste Audits' developed by the US Department of Agriculture [34], and integrate the validated self-assessment procedures proposed by Derqui and Fernández [16] specifically for school canteens.

Acceptability measurement via a 5-level facial hedonic scale follows internationally recognised approaches for pediatric populations. These scales are established as feasible and valid tools for capturing children’s food preferences in real-word canteen settings, minimizing cognitive burden while maintaining high sensitivity to students satisfaction [11]

To ensure the highest quality of scientific communication, this protocol and all future publications arising from this project adhere to established international reporting guidelines:

• −Quantitative components: follow the STROBE to ensure transparent reporting of nutritional epidemiology data [30].
• −Qualitative components: adhere to SRQR guidelines, providing a transparent audit trail of thematic analysis and researcher reflexivity [21,22].
• −Mixed-Methods integration: this study design and subsequent synthesis of findings follow the GRAMMS framework, ensuring a clear description of the “connecting” and “merging” processes used to derive meta-inferences [20].

Protocol validation

The methodological rigor of this protocol is grounded in the integration of “gold standard” quantitative techniques with a systematic qualitative explanatory component, expert consensus and validated instruments.

The evaluation framework for school menu compliance (Phase 1) was co-designed and validated through consensus process between researchers from the Universitat Oberta de Catalunya (UOC) and the Public Health Agency of Barcelona (ASPB). This ensured that the assessment grid and indicators were aligned with both RD 315/2025 and MEMSS programme.

The specific menu evaluation procedure was piloted in a sample of 23 schools during the preparatory phase, which enabled the optimisation of the data collection templates and the standardisation of the peer-review process. The final assessment of menu compliance is carried out via a structured peer review conducted by trained personnel, with discrepancies resolved by a third reviewer to ensure homogeneity and inter-rater reliability.

The quantification of edible plate waste (Phase 2) utilizes direct physical weighing, recognised as the most accurate method for institutional catering and school settings. The use of calibrated scales (±0.1 g) eliminates the recall and estimation biases inherent in visual or self-reported methods, consistent with the reference methodologies of Buzby & Guthrie and Derqui & Fernández [16].

The 5-level facial hedonic scale (Phase 2) is used based on its high feasibility and validity in pediatric populations, and it is widely employed in studies of food and product palatability and school menu acceptance. Systematic reviews highlight facial hedonic scales as one of the most commonly used and internationally accepted instruments for assessing children’s liking and satisfaction, due to their simplicity, visual nature and suitability for different literacy levels. Its concurrent application with physical weighing provides construct validity, linking subjective satisfactions with objective behaviour.

The qualitative phase (Phase 3) is validated through the application of Thematic Analysis (Braun & Clarke) and the use of MAXQDA software for systematic coding, following established procedures in qualitative public health and food waste research.

This rigorous qualitative component enables the protocol to move beyond descriptive quantification of waste and acceptability, generating explanatory insights into the drivers, barriers and contextual factors underlying the observed patterns, and thereby enhancing the overall validity and usefulness of the mixed-methods approach.

Limitations

Reducing FW, and quantifying it, can help bridge the gap between the ideal school menu and students' actual food intake, leading to an improvement in their diets.

While this protocol provides a robust framework for assessing school meal programmes, several limitations regarding its implementation and interpretability should be acknowledged:

• −Direct PW weighing requires intensive coordination and stable canteen routines. In high-volume settings, the weighing process may interfere with the meal service flow.
• −The protocol focuses exclusively on PW. It does not systematically quantify upstream losses (e.g., kitchen preparation waste, surplus unserved food). Consequently, the results do not capture the total food waste of the entire school catering system.
• −The acceptability assessment relies on children’s self-reported liking. Despite using validated facial scales, responses may be influenced by researcher presence, social desirability, peer pressure or scale-usage biases.
• −The findings from FGD are inherently dependent on the participants’ willingness to share authentic views.
• −This protocol was developed and piloted within the Spanish public school system, specifically under MEMSS programme framework. Transferability to international settings may require adaptation to local dietary guidelines, different service models and varying cultural perceptions of school meals.

Related research article

none.

CRediT author statement

Nadia San Onofre, Anna Bach-Faig: Conceptualization, Supervision, Project administration, Funding acquisition.

Alba González-Gallego, Sergi Fàbregues, Gemma Chiva-Blanch, Anna Bach-Faig, Nadia San Onofre: Methodology, Software. Resources.

Anna Pérez-Giménez, Maria Tarafa Orpinell, Silvia Fernández-Barrés, Maria Blanquer, Carles Ariza: Validation.

Alba González-Gallego, Sergi Fàbregues, Anna Bach-Faig, Nadia San Onofre: Formal analysis, Data Curation, Writing - Original Draft, Visualization.

Alba González-Gallego, Sergi Fàbregues, Victor M. González-Chordá, Gemma Chiva-Blanch, Anna Pérez-Giménez, Maria Tarafa Orpinell, Silvia Fernández-Barrés, Maria Blanquer, Carles Ariza, Anna Bach-Faig, Nadia San Onofre: Writing -Review & Editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Data will be made available on request.