There is a need to investigate how adopting different strategies for treating obesity in different countries in the European Union affects the psychological well-being of patients.

The aim of this study was to perform a comparative evaluation of psychiatric symptoms (depression, anxiety and stress) in patients undergoing bariatric surgery versus patients receiving conservative treatment for morbid obesity in Poland and Germany.

A multicentre international prospective cohort study with 155 patients who underwent bariatric surgery and 409 patients who received conservative weight reduction treatment. Evaluation of the psychiatric symptoms was carried out for each patient at baseline and after 12 months of active treatment using a standardised Depression Anxiety Stress Scale questionnaire (DASS-21) questionnaire.

After 12 months of active treatment, the level of psychiatric symptoms (depression, anxiety and stress) significantly decreased in both groups of patients: surgically treated versus conservatively treated patients from Poland and also from Germany. The median change in level of psychiatric symptoms among patients from both countries was significantly higher among surgically treated patients compared with conservatively treated patients (Poland P < 0.0001; Germany P < 0.0001). Improvements in the patient's mental health as a consequence of treatment were dependent on the specific strategy for treating obesity adopted in the analysed countries, the percentage of total weight loss and on gender.

The use of bariatric surgery in both Poland and Germany compared with non-surgical treatment for obesity resulted in more measurable benefits in the form of a decrease in psychiatric symptoms (depression, anxiety and stress) and reduction in body weight.