Health inequalities remain resistant to interventions that primarily target individual behaviour. Although systems approaches are increasingly promoted, their application in practice is often not well grounded in real-world settings. In this protocol paper, we present the approach we will take in an overarching project that synthesises the combined insights of four ongoing systems-based research projects on system-based approaches for reducing health inequalities in the Netherlands. By bringing together and comparing findings across diverse contexts, populations and interventions, we aim to generate an empirically grounded understanding of what works, for whom, in what contexts and why, and to derive actionable strategies for systemic change to reduce health inequalities.

We use a realist approach to synthesise insights from the four ongoing projects. The design involves four iterative steps: (1) Identifying cross-cutting themes from project proposals and literature, (2) Developing and refining context–mechanism–outcome (CMO) configurations through literature review and Slow Science meetings, (3) Engaging Critical Friends to co-develop actionable strategies and (4) Assessing and validating these strategies across diverse contexts. Iterative feedback loops ensure continuous refinement, integration of stakeholder perspectives and exploration of emergent challenges. This design enables theory-informed, practice-based strategies to support sustainable system change in reducing health inequalities.

Ethical approval for the four underlying projects has been obtained from the relevant institutional review boards, and the way their data is used for this overarching project falls within their approved scope. Dissemination will be ongoing and co-created with stakeholders, including policy briefs, factsheets, educational tools and academic publications, to support uptake of strategies for systems change.

Body contouring surgery (BCS) can be applied to reduce the physical and mental burden of excess skin after massive weight loss. Self-reported outcomes of patients are used to assess this burden and to evaluate the effectiveness of BCS. The aim of this study is to clarify what is reflected in self-reports of excess skin after bariatric surgery. We hypothesise that the self-reported burden of excess skin is associated with both objectively assessed excess skin and the disposition to experience negative emotions.

This cross-sectional study will include 68 outpatients presenting at a plastic surgery clinic with a request for BCS. Patients fill out two questionnaires (the BODY-Q and the Sahlgrenska Excess Skin Questionnaire (SESQ)) to measure the size and burden of excess skin as well as the Big Five Inventory (BFI) to measure the disposition towards negative emotionality. Anonymised photographs of excess skin will be rated independently by four plastic surgeons using the Pittsburgh Rating Scale (PRS) Rainbow Classification to establish the objective amount of excess skin. Multiple linear regression analyses will be performed to identify the association of BODY-Q and SESQ scores with objective appraisals of excess skin by plastic surgeons, negative emotionality and demographics. Interobserver agreement for PRS Rainbow Classification will be established by Fleiss’ kappa.

Ethical approval was obtained from the regional medical ethics committee (METC; W20.258) and the institutional review board (Lokale Toetsing, St. Antonius Hospital in Nieuwegein, no. Z23.035). Informed consent of participants will be obtained. The results of this study will be submitted for publication in a peer-reviewed journal.