To better understand the relationship between gut barrier function and the symptomatology and pathophysiology of irritable bowel syndrome (IBS).

Inclusion criteria

• Age 18 to 70 years
• No abdominal surgery (except appendectomy, cholecystectomy, hernia repair, hysterectomy, and C-section).
• Written informed consent

Exclusion criteria

• Females who are pregnant or breastfeeding
• Use of tobacco products within the past 6 months (since nicotine may affect intestinal permeability)
• Use of NSAIDs or aspirin within the past week (since NSAIDs affect intestinal permeability)
• Use of oral corticosteroids within the previous 6 weeks
• Ingestion of artificial sweeteners such as Splenda (sucralose), Nutrasweet (aspartame), lactulose or mannitol 2 days before the study tests begins, e.g. foods to be avoided are sugarless gyms or mints and diet soda.
• Ingestion of any prescription, over the counter, or herbal medications which can affect gastrointestinal transit 7 days before the study begins.
• Proton pump inhibitors.
• Antibiotics for the preceding 60 days before the start of the study.
• (vii) Alcohol intake beyond the recommended safe limit (<21 unites per week)
• Bleeding disorders or medications that increase risk of bleeding from mucosal biopsies.
• Known allergy to fluorescein
• Inflammatory bowel diseases, celiac disease.