Dietary Triggers of Gastrointestinal Symptoms in IBS Patients

This crossover randomized controlled trial will evaluate the effects of gluten and gluten combined with amylase-trypsin inhibitors (ATIs) on inducing intestinal and extra-intestinal symptoms in irritable bowel syndrome (IBS) patients. All participants will be put on a gluten-free diet and then challenged with muesli bars containing either purified gluten, gluten with ATIs, or nocebo.

Irritable bowel syndrome (IBS) is a heterogenous, common gastrointestinal disorder characterized by chronic abdominal pain and altered bowel habits. Many IBS patients report symptom relief on a gluten-free diet (GFD), but it is uncertain whether gluten is the true culprit. The gluten-containing grains wheat, rye, and barley all contain amylase-trypsin inhibitors (ATIs), and a GFD is virtually ATI-free.

This double-blinded crossover randomized controlled trial aims to determine which IBS patients are affected by pure gluten and which are affected by gluten combined with ATIs. IBS patients who respond to and have been on a GFD for 3+ weeks will be randomized to receive a dietary challenge of muesli bars containing either 1) pure gluten, 2) non-purified gluten (containing ATIs), 3) or nocebo for a week followed by a 14 day washout. This will be repeated until all participants have had each dietary challenge.

The study will evaluate the effects and potential mechanisms of purified and non-purified gluten on intestinal and extra-intestinal symptoms in IBS. It is likely that some IBS patients respond to gluten, while others respond to gluten combined with ATIs. Thus, this project may lead to better diagnosis and individualized dietary treatments for IBS.

Eligibility Criteria:
Inclusion Criteria:

* IBS diagnosis based on Rome IV criteria.
* Asymptomatic on a gluten-free diet (IBS-SSS score 0-74).
* Compliance with the study procedures (according to the investigator's own judgement).
* Signing the Study Informed Consent form.

Exclusion Criteria:

* Concurrent systemic disease and/or laboratory abnormalities considered by investigators to be risky or that could interfere with data collection.
* Concurrent organic gastrointestinal disease (i.e. Celiac disease, Inflammatory Bowel Disease, peptic ulcer disease, etc.) other than benign polyps, diverticulosis, hemorrhoids, lipoma and melanosis coli.
* Major abdominal surgery with the exception of hernia repair, appendectomy, Caesarian section, tubal ligation, cholecystectomy, hysterectomy, and hemorrhoidectomy.
* History of active cancer in the last 5 years, other than skin basal cells cancer.
* Pregnant or breastfeeding women.
* Current use of antibiotics or antibiotic treatment within 1 months before the first visit.
* Consumption of probiotics within 1 month prior to the first visit.
* Use of non-authorized medications (see Unauthorized Medications section).
* Patients on a high fibre diet (\>35 g/day for males, \> 25 g/day for females), consuming high inulin containing foods (\>5 g/day), and/or consuming dietary fibre supplements (as assessed by dietary assessment questionnaire) in the 4 weeks prior to the first visit.
* Patients currently participating or having participated in a trial within the past month.