In this study, the investigators aim to assess the effect of acute FODMAP infusion on gastric motility and on gastrointestinal and psychological symptoms. This is a randomised, single-blinded, crossover study of different solutions, differing in FODMAP content. The four solutions that will be tested in healthy volunteers are (1) a fructan solution, (2) a fructose solution, (3) a FODMAP mix and (4) a glucose solution as a control. In IBS patients, only the fructan and glucose solution will be tested, where after they can choose to come for a third visit to test the fructose solution. The different solutions will be tested on separate occasions, three days to one week apart, in a randomised order.

The preparation of each study visit will be identical. After an overnight fast, participants will be asked to come to the clinic. To ensure a low baseline symptom level and low microbial gut activity, a diet low in fibre and fermentable carbohydrates will be followed the day prior to each test (information will be provided to assist this). Participants will be asked to refrain from alcohol, tea and coffee, and intense physical activity for at least 12 hours before participation. They will also be asked to refrain from smoking cigarettes at least one hour before the start of the experiment.

A high resolution manometry probe will be inserted through the nose into the stomach of the participant to assess intragastric pressure as a measure of gastric motility and gastric accommodation. In addition, an infusion tube will be positioned in the proximal stomach to administer the solution. The position of the probes will be checked fluoroscopically (maximum 15 seconds). In this case, relevant guidelines of radioprotection will be adhered to. Patients will be protected by a lead shield that covers the lower abdomen and all personnel will wear a lead jacket. After the catheters are fixed to the subjects' chin, the patients will be asked to sit at a table and remain in this position for the remainder of the experiment.

After a stabilization period of at least 15 minutes, and when the subject is in phase II of the hunger cycle, one of four solutions will be intragastrically administered at a constant speed of 60 mL per minute (determined by an automated system using a peristaltic pump). IGP will be recorded for the duration of the drink infusion and for the following 3 hours. During infusion, the subjects will be asked to score their satiation at 1-minute intervals using a graphic rating scale that combines verbal descriptors on a scale graded of 0-5 (1, threshold; 5, maximum satiety). The intragastric infusion will be stopped as soon as a score of 5 is reached on their satiation scores. In addition, participants will be asked to complete a gastrointestinal symptom questionnaire every 15 minutes. The participant's emotions and mood will be assessed before, immediately after and 1, 2 and 3 hours after infusion, using the State-Trait Anxiety Inventory (STAI) and the validated Dutch version of the Positive and Negative Affect Scale (PANAS). Emotional state will be repeatedly measured every 15 minutes using the Self-Assessment Manikin (SAM) and Profile of Mood States (POMS)-Fatigue subscale.