Carbohydrate metabolism was studied in morbidly obese (MO) patients (n=22), in patients who underwent biliopancreatic diversion/duodenal switch (BPD/DS) (n=23) and in the control group (n=22). Blood glucose levels, IRI, GLP-1, GIP and glucagon during the OGTT (with 75 g glucose) at 0, 30, 60 and 120 min. were measured. In MO patients impaired glucose metabolism was revealed in 15 cases (68.2%); in the BPD group, postprandial blood glucose levels (120 min) tended to be lower compared to the other groups: 4 individuals (17.4%) even showed postprandial hypoglycemia (<2.8 mmol/l). Basal and peak GLP-1 levels were significantly higher after BPD/DS (ÃÆââ¬ËÃâââ¬=0.037 and p=0.022, respectively). Morbidly obese patients had higher GIP values at all points. The basal glucagon concentrations were similar in the postsurgery and the control groups, while morbidly obese patients had higher initial levels of glucagon (p=0.013) and it was not suppressed during the OGTT (p=0.076). Impaired carbohydrate metabolism in MO patients is characterized by hyperglucagonemia, increased GIP levels and decreased GLP-1 secretion. Patients who underwent BPD/DS revealed a significantly higher IRI and GPP-1 secretion, which poses a high risk of postprandial hypoglycemia.