Background: Obesity is associated with multiple diseases. Bariatric surgery is the most effective therapy for severe obesity that cannot only reduce body weight but also obesity-associated morbidity.

Objective: The metabolic alterations associated with obesity and respective changes after bariatric surgery are incompletely understood.

Design: In the longitudinal observational study, the investigator applied a 1H-NMR-based global, untargeted metabolomics strategy on human serum samples that were collected before and repeatedly up to one year after distinct bariatric procedures (sleeve gastrectomy, proximal and distal Roux-en Y gastric bypass; RYGB). For comparison, the investigator also analyzed serum samples from normal-weight and less obesity obese subjects that were matched for 1-year postoperative BMI values of the surgical groups.

Inclusion Criteria:

• BMI >/=35 kg/m2
• at least 2 years of unsuccessful conservative weight loss attempts

Exclusion Criteria:

• < 18 years of age
• BMI < 35 kg/m2
• informed consent was not signed by the patient

severely obese patients of the Interdisciplinary Obesity Center, St. Gallen, Switzerland