The Effect of Dietary Supplementation on Intestinal Barrier Function in IBS-D

Inclusion Criteria: 1. Participant has provided written informed consent before participating in the study after being given a full description of the study and prior to any study-specific procedures being performed. 2. Participant has irritable bowel syndrome with diarrhoea (IBS-D), as defined by the Rome IV criteria, confirmed by bowel diary. 3. Participant has an IBS-SSS score of \>175 4. LPS at screening \>0.21 ng/ml. 5. Participant is a male or non-pregnant female and is 18-70 years of age 6. If WOCBP participant is willing to adhere to one of the following methods of contraception i) Hormonal contraception e.g. the 'pill' or an implant ii) Intrauterine device (IUD) iii) Intrauterine hormone-releasing system (IUS) iv) Hysterectomy v) Vasectomised partner vi) Sexual abstinence (if it is in line with your preferred and usual lifestyle). 7. Participant can communicate well with the Investigator and to comply with the requirements for the entire study. 8. Participant has capacity to understand written English. 9. Participant has a body mass index (BMI) of 18.5 - 39.9kg/m2 (bounds included). 10. Participant agrees to follow all pre-test preparation before L/M testing. Exclusion Criteria: 1. Prior abdominal surgery other than appendectomy, tubal ligation, hysterectomy or cholecystectomy. 2. Participated in a trial of an investigational medical product or medical device in the last 28 days. 3. Females who report to be pregnant or lactating 4. Unwilling to maintain stable doses of permitted concomitant medication. 5. Unwilling to maintain a stable diet for the duration of the trial. 6. Being in the opinion of the investigator unsuitable 7. Insufficient knowledge of English to complete the daily bowel diary and food diary. 8. Hypersensitivity to any component of the supplement 9. Hypersensitivity or known allergy to lactulose or mannitol. 10. Consumption of oral antibiotics in the last 2 weeks. 11. NSAIDs for 2 weeks prior to and during the entire 21 day study period. Participant should not be a chronic NSAID user (\>1 day/week). 12. Participants who have received bowel preparation for investigative procedures in the 4 weeks prior to the study. 13. Diabetes mellitus (type 1). 14. Participants with known hepatic disease. 15. Inflammatory bowel disease (Crohn's/Colitis) or coeliac disease. 16. Gastrointestinal infection in the past 4 weeks. 17. Any other condition, deemed by the investigator, that may be causing their symptoms. 18. Participant is involved in this study as an Investigator, sub-Investigator, study coordinator, other study staff, or Sponsor member. 19. Participant is unable to adhere to withholding in endurance exercise, such as \>45 minutes of high intensity running, cycling, rowing etc, from the screening phone call to the end of study visit.