Purpose The aim of this study was to analyze the microbiota of patients undergoing LSG or LRYGB on three levels of gastrointestinal tract, using oral swab and stool sample. We compared samples from patients achieving favorable outcomes in terms of weight-loss with patients, who did not respond optimally to the bariatric operation.

Materials and methods Design This prospective cohort study was conducted in one academic, teaching hospital. The recommendations of the Metabolic and Bariatric Surgery Section of the Polish Surgical Society were used as indication for surgery, that is: Body Mass Index (BMI) ≥35 kg/m2 with obesity-related comorbidities or BMI ≥40 kg/m2 .

Analysis and endpoints Primary endpoint was to determine the difference in microbiota present in oral cavity and large intestine between patients ing Group 1 and Group 2. Secondary endpoint was to compare the results of microbiota analysis between LSG and LRYGB.

Inclusion Criteria:

• informed consent to participate in the study, meeting the eligibility criteria for bariatric treatment, either for LSG or LRYGB.

Exclusion Criteria:

• type 1 or type 2 diabetes, treatment with antibiotics within 30 days prior to gathering microbiological material, treatment with probiotics within 30 days prior to gathering microbiological material, gastrointestinal infections, inflammatory bowel disease, thyroid diseases, cancer (especially the digestive tract), immunodeficiency.

The investigators included patients undergoing surgical treatment for morbid obesity.

We are not planing to share data.