Irritable bowel syndrome is a functional lower gastrointestinal disorder characterised by abdominal pain and altered bowel habit in the absence of organic pathology to explain the symptoms. Irritable bowel syndrome has a prevalence of approximately 10% in adults, shows a female preponderance, and is more common in younger individuals. In clinical practice, Irritable bowel syndrome accounts for almost a third of all gastroenterology cases seen in primary care, with a subsequent third of these being referred onto secondary-care for further evaluation. The economic burden of Irritable bowel syndrome, in terms of medical expense, work absenteeism and loss of productivity, is considerable.

The exact cause of irritable bowel syndrome is unknown. Accordingly there has been a huge surge in interest for dietary therapies to help manage Irritable bowel syndrome. To date, there are only a handful of small randomized controlled trials evaluating the efficacy of dietary therapy in Irritable bowel syndrome. In light of this we plan to conduct the first randomized controlled trial directly comparing the effectiveness of the low-FODMAP diet, British Dietetic Association diet, and the gluten free diet in Irritable bowel syndrome. Moreover, such a trial allows for a direct comparison of nutritional and gut microbial changes, both of which can suffer detrimental consequences following the implementation of restrictive dietary therapies. This study is also unique in that it takes into consideration the patients' perspective with regards to the convenience and cost-effectiveness of implementing such diets into routine day-to-day life. The study will aim to recruit 100 patients from Sheffield Teaching Hospitals gastrointestinal clinics. Following recruitment patients will be seen by a hospital dietitian where they will be randomized to one of the 3 diets. Participants will complete a questionnaire portfolio weekly for one month as part of the study

Inclusion Criteria:

1. Irritable Bowel syndrome - as defined by abdominal pain and altered bowel habit in the absence of organic pathology to explain the symptoms.This is the contemporary definition as provided by the Rome IV committee.
2. Age 18-65 years
3. English literate
4. Can travel to hospital
5. Telephone/internet access

Exclusion Criteria:

1. Inflammatory bowel disease
2. Coeliac disease
3. Gastrointestinal cancer
4. Previous abdominal surgery
5. Scleroderma
6. Poorly controlled diabetes
7. Severe liver disease
8. Severe renal disease
9. Severe respiratory disease
10. Severe cardiac disease
11. Severe psychiatric disease
12. Memory disorders
13. Pregnant
14. Current dietary interventions
15. Recent/current use of Probiotics
16. Recent/current use of Antibiotics
17. Recent/current use of Narcotics
18. Currently titrated antidepressants (i.e. not on a stable dose)

IPD will not be shared