The Effect of Two Probiotic Products on the Intestinal Barrier Function in Patients With Irritable Bowel Syndrome

Inclusion Criteria: * Signed informed consent * Fulfilled Rome IV diagnostic criteria for IBS with predominant diarrhoea * Mild-to-severe IBS symptoms according to the IBS severity scoring system (IBS-SSS; a score of ≥75) * Age: 18-65 years Exclusion Criteria: 1. Known organic gastrointestinal disease (e.g. inflammatory bowel disease, IBD) 2. Previous abdominal surgery which might influence gastrointestinal function, except appendectomy and cholecystectomy 3. History of or present gastrointestinal malignancy or polyposis 4. Recently (within the last 6 months) diagnosed gastrointestinal infection 5. Current diagnosis of dementia, severe depression, major psychiatric disorder, or other incapacity for adequate cooperation 6. Chronic neurological/neurodegenerative diseases (e.g. Parkinson's disease, multiple sclerosis) 7. Autoimmune disease and/or patients receiving immunosuppressive medications 8. Chronic pain syndromes (e.g. fibromyalgia) 9. Chronic fatigue syndrome 10. Severe endometriosis 11. Coeliac disease 12. Recently (within the last 3 months) diagnosed lactose intolerance 13. Females who are pregnant or breast-feeding 14. Regular intake of systemic corticosteroids and anti-inflammatory medication (including non-steroidal anti-inflammatory drugs, NSAIDs) during the last 3 months or incidental use in the last 2 weeks prior to randomisation 15. Recent (\< 4 weeks) intake of proton pump inhibitors, PPIs (e.g., omeprazol) 16. Use of anti-depressants in the last 3 months 17. Regular oral intake of mast cell stabilising drugs (e.g. sodium cromoglycate) during the last 3 months or incidental use in the last 2 weeks prior to screening 18. Antimicrobial treatment 6 weeks prior to first screening visit 19. Antimicrobial prophylaxis (eg. acne, urinary tract infection) 20. Regular consumption of probiotic products 4 weeks prior to first baseline visit 21. Concurrent or recent (\<4 weeks) use of nutritional supplements or herb products affecting intestinal function (e.g. aloe vera, St. John´s Wort, fibres, prebiotics) if the investigator considers those could affect the study outcome. 22. Inability to maintain exercise routine and dietary pattern during the study. 23. Abuse of alcohol or drugs 24. Any clinically significant present or past disease/condition which in the investigator's opinion could interfere with the results of the trial