The long-term success of metabolic and bariatric surgery (MBS) depends largely on adherence to health-promoting behaviour following MBS. Especially, adherence to healthy dietary behaviour in line with guidelines appears to be of the utmost importance. The primary objective of the present study is to evaluate the effect of adherence to dietary behaviour recommendations and the percentage of total weight loss (%TWL) after MBS. Adherence is hypothesised to have a positive influence on the %TWL, 24 months after MBS. Furthermore, we investigate the association of various sociodemographic, organisational, psychological and behavioural factors prior to and after MBS and their effect on %TWL.

The present study is a single-centre observational, prospective, longitudinal cohort study conducted in Germany. Data are collected at nine measurement points (T0: 4 weeks prior to MBS; T1: 2 weeks after MBS, T2: 5 weeks after MBS; T3: 3 months after MBS; T4: 6 months after MBS; T5: 12 months after MBS; T6: 18 months after MBS; T7: 24 months after MBS; and T8: 36 months after MBS). Adherence to dietary behaviour recommendations is assessed using the Dietary Behavior Inventory-Surgery (DBI-S). N=325 patients applying for MBS will be included in the study. A regression analysis approach is chosen to answer the primary research question. The primary outcome %TWL is regressed at T7 (24 months after MBS) in a causal analysis on dietary adherence (DBI-S score) at T3–T7, with the covariates age, gender, marital status, educational attainment, employment status, Patient Health Questionnaire-4 score and body mass index at T0 and MBS method at T1. Stepwise hierarchical regression analyses are performed and analysed for significant model differences using ² difference tests. Effect sizes are estimated by R². Group differences are analysed using t-tests and Analyses of variance (ANOVAs). Bivariate correlations of continuous variables are examined using regression/correlation analyses.

The Ethics Committee of the Medical Faculty of the University of Essen-Duisburg has approved the conduct of the study (24-11969-BO). Results will be disseminated through manuscripts in clinical/academic peer-reviewed journals, presentations at academic conferences and communications with partners, participants and other stakeholders. Key findings will also be published in lay language on a publicly accessible website and disseminated via various (social) media channels.

The study has been prospectively registered on 8 October 2024 in the German Clinical Trials Register (DRKS00034888).

About one-third of all patients with cancer in Germany are still of working age at the time of diagnosis. Therefore, occupational reintegration is an important goal after the completion of the treatment. Compared with the general population, patients with cancer are more frequently affected by unemployment, early retirement and reduced earning capacity pensions. Yet, there are no robust results about which factors determine occupational reintegration, whether downward social mobility is associated with a cancer diagnosis and which groups are particularly at risk for not returning to work or the loss of their social position. The aim of this study is to analyse social inequalities in occupational reintegration, work-related changes and vertical social mobility processes, as well as to explore the role of rehabilitative measures and other intermediary influences in these processes.

Data are collected in a retrospective cross-sectional study with a qualitative in-depth sequential mixed-methods design. For this purpose, patients from three federal states in Central Germany who have been diagnosed with cancer between 2017 and 2022 and are between 18 and 60 years will be asked to participate in this study. Participants answer a standardised questionnaire (written or online). A subsample will subsequently be questioned in a qualitative interview.

Analysis will be done by descriptive and multivariate methods as well as qualitative content analysis.

Ethics approval has been obtained from the Ethics Committee of the Medical Faculty at the Martin Luther University Halle-Wittenberg (reference number 2023-117). All research activities will be performed in accordance with the Declaration of Helsinki. Participants have to provide informed consent before enrolment. The study is registered at the German Clinical Trials Register. Results will be presented in peer-reviewed academic journals, at (international) conferences and on a joint workshop with stakeholders and patients.

DRKS00032076.