Background: Methods based in system dynamics (SD) have gained prominence within public health research in recent years. SD is grounded in theory and explains how central principles, such as adaptation, dynamics and emergence can be used to understand and/or change complex systems. To date, few examples exist where this theory has been applied consistently in a prevention approach in a local context. This study aimed to reflect upon the application of theoretical SD principles in context of the Lifestyle Innovations Based on Youth Knowledge and Experience (LIKE) project. Methods: A multi-methods qualitative evaluation was conducted using the LIKE project, situated in Amsterdam, the Netherlands, as a case study. LIKE applied a participatory system dynamics approach for obesity prevention in youth, throughout the project during a time period of 6 years (2017–2023). Data collection included document reviews, a Ripple Effects Mapping workshop, and semi-structured interviews with involved stakeholders, followed by in-depth reflective analysis. Results: We identify three key lessons combining theory and practice: (1) theory: interdependency programme and context; lesson: avoid becoming overly focused on achieving a complete understanding of the system related to the topic under study (for example, obesity). Instead, ensure sufficient attention is given to comprehending the dynamics of the local context, including existing initiatives and policy processes; (2) theory: dynamic and adaptive character; lesson: while the ability to encompass real-world dynamics is a foundational strength of system dynamics theory, its practical application can be constrained by more static elements, such as budget planning, and the need for clearly defined roles and responsibilities; and (3) theory: strong governance; lesson: SD projects require strong governance including strategic planning and enduring commitment, but in the absence of clear milestones or measurable impact on the short term. Conclusions: Applying SD principles in practice requires a collective shift in thinking and working for all parties involved. Challenges in particular relate to the many uncertainties that arise whereby everything continues to change over time, including the focus of the system under study; relevant stakeholders; and momentum for change. This necessitates strategies different from our accustomed linear research working practices, shifting instead towards more iterative approaches that accommodate complexity and uncertainty. [ABSTRACT FROM AUTHOR]

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