This study bases on the successfully completed project SNF 320000-112006 (EK 1152 and SwissMedic 2005dr2207e) and will document the physiological effects of inhibited gastric secretion on the volume as well as the acidity of gastric secretion by high dose proton pump inhibitors in GERD patients and healthy controls. Twelve participants in each group will be studied in a randomized, double-blind placebo controlled trial. A novel non-invasive MRI technique developed in Zurich will assess the volume of gastric secretion following the ingestion of a regular liquid meal. In addition, intragastric / esophageal pH monitoring will assess the link between volume and intragastric distribution of gastric secretion on reflux events and symptoms. In addition, the effect of gastric secretion on outcome parameters of a non-invasive stable isotope breath test for measurement of gastric emptying will be assessed.