The primary objective of this study is to assess the effect of the natural course of postprandial hypoglycemia vs. a postprandial euglycaemic condition on driving performance in individuals with confirmed postprandial hyperinsulinaemic hypoglycaemia after gastric-bypass surgery.

Despite the increasing prevalence of postprandial hyperinsulinaemic hypoglycaemia (PHH), clinical implications are still unclear. Anecdotal evidence from patients with PHH suggest a high burden for these patients due to the recurrent hypoglycaemias with possibly debilitating consequences. It is well established, that even mild hypoglycaemia (plasma glucose of 3.4mmol/l) in diabetic and non-diabetic significantly impairs cognitive-motor functioning. Of note, some of the cognitive aspects remain impaired for up to 75min, even when the hypoglycaemia is corrected. In addition to the hypoglycaemic blood glucose levels per se, the dynamics of the hypoglycaemia occurrence appears to play a role. It was shown in individuals with type 1 diabetes, that cognitive functions are affected more during a fast-fall than slow fall hypoglycaemia in the postprandial state.

Driving is a frequent daily activity which integrates various mental function including visual and auditory processing, motor skills, reasoning and problem solving. Due to the potentially dangerous consequences, avoidance of hypoglycaemia-induced driving mishaps is of uttermost importance. Several studies have evaluated the impact of induced, controlled hypoglycaemia in individuals with type 1 diabetes on driving performance using driving simulators but data in PHH patients are currently lacking. Assessing the potential impact of the natural course of postprandial hypoglycaemia on driving performance in PHH patients will contribute to a better understanding of the consequences and relevance of this problem. The investigator will test the hypothesis whether driving performance during the postprandial glucose dynamics is impaired in patients with confirmed PHH.

Inclusion Criteria:

• Aged ≥18 years
• Roux-en-Y gastric bypass ≥1 year ago
• PHH defined as postprandial plasma or sensor glucose<3.0mmol/l according to the International Hypoglycaemia Study Group (1) and exclusion of other causes of hypoglycaemia
• Possession of a valid Swiss driver's license. Passed driver's examination at least 3 years before study inclusion. Active driving in the last 6 months before the study.

Exclusion Criteria:

• Clinically relevant weight changes (≥5%) within the past 3 months
• Incapacity to give informant consent
• Historical or current diabetes based on HbA1c ≥6.5% without glucose-lowering treatment
• Haemoglobin level below 11 g/dl
• Ongoing treatment with glucose-lowering drugs, anorectic drugs, steroids or any medications known to affect gastric motility
• Active heart, lung, liver, gastrointestinal, renal or neurological disease
• Inability to follow study procedures
• Pregnancy or breast-feeding

Participants will be masked to the type of beverage ingested at each visit (200ml of water containing glucose or aspartame). Furthermore, participants will be masked to glucose levels throughout the study