**5. Conclusions**

This study adds to the existing body of research by identifying inhibitory and promotive factors for HRQOL and self-concept in the context of childhood obesity, with implications for therapy and care. The results identify physical fitness as a key predictor of weight-specific HRQOL and subdomains of self-concept of children and adolescents with obesity. These findings suggest that improvements in physical fitness may hold even more promise for positive psychosocial health outcomes in weight management programs

than weight loss or participation in physical activity alone. In addition, addressing at-risk children from lower socioeconomic or migration backgrounds at an early stage might be crucial not only to prevent obesity but also to improve mental health. Our findings furthermore indicate that strategies to promote body satisfaction and motor abilities could be critical especially in adolescence to improve the physical self-concept of adolescents with overweight and obesity but future longitudinal studies are required to investigate the robustness and causality of our findings.

**Supplementary Materials:** The following materials are available online at https://www.mdpi.com/ article/10.3390/ijerph182111188/s1, Table S1: Baseline Multivariable Linear Regression Models.

**Author Contributions:** N.E. analyzed the data and wrote the manuscript. C.J. supervised the analysis, provided methodological guidance, and revised the manuscript. D.F., M.K. and F.H. (who work as sports scientists in the program) and L.S. and S.V. (who are responsible for the areas of nutrition and psychology in the program) conducted the medical tests and gathered the data. C.J. is the leader of the CHILT III program and created the study design. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research did not receive any financial support from funding agencies in the public, commercial, or not-for-profit sectors.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee Ethics of the German Sport University Cologne for the ethic request with the number 107/2014 which was updated on 17 May 2021 ("Children's Health InterventionaL Trial III—ein ambulantes, multimodales, familienbasiertes Schulungsprorgamm zur Therapie von Ubergewicht und Adipositas im Kindes- und Jugendalter").

**Informed Consent Statement:** Informed consent was obtained from the participants' parents.

**Data Availability Statement:** The data used and analyzed during the current study involve sensitive patient information and indirect identifiers. As a result, the datasets are available from the corresponding author only on reasonable request.

**Acknowledgments:** We gratefully acknowledge all CHILT III participants and their parents. We would also like to thank Hidayet Oruc and Jonas Juretzko for their support during the program and Selina Müller for her help in researching and calculating the HROQL scores.

**Conflicts of Interest:** The authors declare no conflict of interest.
