Explaining and disseminating the study design is necessary to show a kind of guide that is useful to other researchers who want to analyze diet inequalities in adolescents in secondary schools. In the case of the qualitative methodology, this type of disseminating is much less frequent than quantitative methodology. For this reason, we think in the pertinence of our proposal.

The theoretical frameworks guiding this project include Rasmussen's1 conceptual framework, the Angelo framework, and the typology of environments proposed by Swinburn et al.2 These conceptual frameworks encompass four relevant dimensions —cultural,3 physical,4 social,5,6 and individual7,8— as influences on diet.

The objective of this article is to describe the design and qualitative methods employed in the Dietary Inequalities and Behaviors in Adolescents project (PID2020-113537RB-I00) within this framework.

The qualitative case study methods used herein follow the interpretative/constructivist paradigm to seek out multiple perspectives.9 The interpretative/constructivist paradigm consists of a case study design combined with grounded theory analysis method that allow the in-depth exploration of factors of diet within context and the generation of a theoretical framework or complementing the consolidated theory.9

The project was funded by the Spanish Ministry of Science and Innovation in 2021 and is being conducted in Madrid and Bilbao through 2024. We chose these two cities because they implied two differentiated dynamics: Madrid could represent a large European city, and Bilbao a medium-sized city. These cities were known by the research group and the members of the project had conduced qualitative researches related to health inequality10,11. One of these researches used very similar criteria to those of the research of this manuscript10.

Data is being gathered through a combination of semi-structured interviews (SSI) and focus groups (FG). These two techniques complement each other and allow us to capture not only individual insights into dietary behaviors during adolescence, but also collective perceptions from social types such as parents, teachers, and adolescents.

First, we conducted 12 SSI with school principals (they were considered key informants) between April and October 2021. We interviewed them to have a comprehensive vision of the school, the neighborhood, and dynamics related to dietary behaviors among adolescents.

Next, we conducted three SSI with students aged 15 through 18 years in each city (n=6) as a kind of pilot study in each city between April and May 2021. Based on these first six SSI, we refined the topic guide for both SSIs and FG.

Both the SSI and FG involving adolescents have been designed according to specific profiles determined by the following criteria: type of educational center (public or private), sex, age, school year, immigration, and ethnic group.

Fieldwork started in April 2022 and will last until December 2023. To date, we have conducted 32 SSI and 12 FG (73 participants). The FG comprise between five and eight participants. These are taking place in the chosen schools. The SSI are lasting between 30 and 45minutes and FGs between 60 and 90minutes. The SSI and FG are coordinated by researchers coauthoring this research.

We developed a common guide for the SSI and FG, with slight variations depending on the target group (adolescents, parents, or teachers). The guide included topics such as: sociodemographic data (age, course that is studied; family environment, family composition and academic level of parents); characteristics of neighborhood and school; uses and resources of neighborhood; dietary behaviors (daily diet, week-end diet, family diet, diet in breakfast, lunch, and dinner); peer group influence; network influence; type of food shops where adolescents buy; physical activity in the school; daily physical activity and perception of environment related to physical activity; influence of the lockdown due to the COVID-19 pandemic in the diet and physical activity. The complete topic guide is included in online supplementary data.

We will use constructivist grounded theory15 and interpretative phenomenological analysis16 to analyze the data. Despite the different epistemological tradition of both theories, in the research team there are members who use the grounded theory in their analyzes and others the interpretive phenomenological analysis. We think that the use of both theories (triangulation of qualitative methods)17 can give a more holistic vision to our project.

The study is being conducted according to the guidelines laid down by the Declaration of Helsinki and ethical approval was granted by the Ethics Committee of the University of the Basque Country (M10_2021_315). Anonymity and confidentially of the participants is guaranteed. We are obtaining written consent for their participation. The inclusion of minors in this study requires an informed consent from the parents.

We designed a qualitative case study to explore the main factors influencing dietary behaviors in adolescents living in two Spanish cities. In this manuscript, we describe the study protocol.

In the time elapsed since the project began, the authors have detected some factors that influence the diet of adolescents, such as gender, family environment, SES and the use of internet and social media. Related to gender, the scientific literature suggests that there are gender disparities in adolescents’ diets, with females tending to adhere to beauty patterns and males to a muscle-building.18 The family environment is related to SES, thus, the family model and, specially, the lack of supervision are factors influencing dietary behaviors in low socioeconomic level areas.19 Finally, digital factors may influence also adolescents’ eating behaviors. According to several publications, internet, mass media and social media conditioned adolescents’ food choices and influenced their self-perception.20,21

Other factors such as the influence of peer group22 and teachers,23 school environment24 and neighborhood environment,25 will probably be found as we progress in our project.

Considering we used a convenience sample, we acknowledge that this case study may not be fully representative of the entire cities of Madrid and Bilbao. Refusals from school may have limited our ability to identify “the most useful” discourses. Due to the high demand in schools in Spain for participating in research studies, projects, etc., they reject many of these proposals.14 In addition, researching within schools presents several challenges, including limited time for FGs, potential bias in selecting interviewees and FG participants, and the lack of neutral spaces to conduct the FGs and SSIs in the schools.26

We believe that the design and methods of Dietary Inequalities and Behaviors in Adolescents study may improve the research dynamics in health issues in adolescents in educational centers as well as the study of determinants of diet. Therefore, the results of this project might provide valuable evidence for developing food and nutrition policies aimed at improving adolescents’ health.

Jorge Marcos Marcos.

J. Rivera made a substantial contribution to the design and elaboration of this manuscript. I.L. González reviewed the first draft of the manuscript and contributed with his important comments to the final version; in addition, designed the map and the table included in the manuscript. G. Ramos contributed with her important comments to the final version. L. Gravina conducted a bibliographical review very important for the writing of this manuscript. J. Díez helped to bibliographical review and to design the map and the table included in the manuscript. Finally, M. Franco contributed with his important comments to the final version.

This work is part of the project “Dietary behaviours in inequalities in adolescents: A qualitative study in secondary schools in Madrid and Bilbao” (reference PID2020-113537RB-I00) funded by the Spanish Ministry of Science and Innovation.

None.