Functional dyspepsia patients will be recruited and screened for inclusion in the study. The participants will be asked to not take proton pump inhibitors, drugs effecting gastric motility and NSAIDs and oral anticonception for fourteen weeks. First, they will stop with their daily drug intake of PPIs and NSAIDs for two weeks, then they will take placebo or UDC for four weeks, two doses every day during lunch and dinner. Afterwards, there will be a washout period of four weeks, and again four weeks of UDC or placebo intake. The patients will receive a diary in which they describe their symptoms/discomforts every day for 14 weeks. All participants and the investigator will be blinded to the nature (UDC or placebo) of the pills. The random order in which a certain patient gets his pills has been decided by the pharmacy of UZ Leuven and is also unknown for the investigator (double blinded). During week two, four, six, eight, ten and twelve we will have a phone conversation with the patients to discuss their symptoms/discomforts.

During week four and week twelve, the patients will come to the hospital for one day after an overnight fast. First, they are asked to fill in a bundle of questionnaires concerning physical complaints, depression, anxiety (disturbances), pain/disease, body/interoceptive awareness, trauma/abuse and personality and to give a fecal sample that they've collected the day before. The fecal sample will be used to evaluate the gastrointestinal microbiota in FD patients. Then, two blood samples, to evaluate liver function parameters and bile acid synthesis, will be taken and an endoscopy will be performed. All endoscopies will be performed by an experienced endoscopist (Jan Tack) and nine duodenal biopsies (2 biopsies at a time) (Radial Jaw™3 with needle; outside diameter 2.2mm; Boston Scientific, 302 Parkway, Global Park, Heredia, Costa Rica) will be obtained. To measure the in vitro transepithelial resistance, 3 biopsies will be examined using an adapted mini-Ussing chambers system. After equilibration, the mucosal side of the tissue will be exposed to 4kDa FITC-dextran as a measure of paracellular permeability. A sample will be taken from the serosal side during 2h at 30min interval. The concentration of fluoresceïn will then be measured using a fluorescence plate reader. Also, two biopsies will be used for mRNA extraction and subsequent cDNA synthesis. This cDNA will be used to measure the gene expression of bile acid receptors by means of real-time RT-PCR. In addition, one biopsy will be prepared for immunohistochemistry and two will be used for western blot to measure changes in distribution/expression of the bile acid receptor proteins. One biopsy will be obtained to study ultrastructural alterations by transmission electron microscopy.

After the endoscopy, an aspiration catheter will be positioned in the duodenum. The position of the catheter will be briefly checked by fluoroscopy (typically 2-3 seconds, however never more than 15 seconds). After positioning of the catheter, it is fixed to the subject's chin and he/she is asked to take place in a chair for the remainder of the experiment. For one hour, every 15 minutes duodenal fluids will be collected during fasted state. Next, a high resolution manometry catheter (HRM) will be placed in the gastric fundus to measure intragastric pressure and a perfusion tube (OD 2 mm) will be introduced through the nose and positioned in the stomach. After positioning of the catheters, they are fixed to the subject's chin and he/she is asked to take place in a chair for the remainder of the experiment. After a stabilization period of 15 minutes, intragastric infusion of the nutrient drink (Nutridrink, Nutricia; 630 KJ, 6 g proteins, 18.4 g carbohydrates, and 5.8 g lipids per 100 mL) will start at a constant speed of 60 mL per minute (determined by an automated system using a peristaltic pump). Intragastric pressure will be measured with a 36-channel high resolution manometry system, through the intragastric manometry probe. At 1-minute intervals, the subjects will be asked to score their satiation using a graphic rating scale that combines verbal descriptors on a scale graded 0-5. At 5-minute intervals the volunteers will be asked to fill out a VAS for 11 dyspeptic symptoms. The intragastric infusion will be stopped as soon as the volunteers score maximally on one of the 11 epigastric symptoms or when a score of 5 is reached on their satiety scores. 10 minutes thereafter, the catheters will be disconnected and removed. After the nutrient drink infusion, duodenal fluids will be collected every 15 minutes for 1.5 hour during fed state. Finally, the last catheter is removed and the volunteer can go home.