Introduction: Multidisciplinary obesity services at university hospitals usually treat patients with more complex and severe obesity. In addition, patients with Class 3 obesity, in particular, have different attitudes regarding the choices of therapy. Methods: This explorative study investigated the effect of patient attitudes towards bariatric surgery on body weight change (primary outcome) and psychological improvement (secondary outcomes: quality of life, depression, anxiety, and eating behaviour) in a 6-month moderate behavioural weight loss (BWL) programme in a university outpatient setting. Results: 297 patients with mostly Class 3 obesity participated in the programme. The patients did not yet have any indications for bariatric surgery. Of the participants, 37% had a positive attitude towards bariatric surgery (POS), whereas 38% had a negative attitude (NEG). The drop-out rate was 8%. NEG participants lost significantly more body weight than the POS participants (intention-to-treat population: 4.5 [SD: 6.3] kg versus 0.4 [SD: 5.8] kg; p < 0.001). In both subgroups, anxiety, depression, the mental score for quality of life, and eating behaviour improved. Conclusion: A BWL treatment in a clinical setting identified 2 distinct groups with different attitudes towards bariatric surgery that were associated with different body weight change outcomes. These groups may require differently targeted programmes to achieve the best body weight loss results.
