Irritable Bowel Syndrom (IBS) affects up to five percent of Canadians and has proven difficult to treat. Our research will explore how a type of dietary carbohydrate, called FODMAPS, contributes to chronic abdominal pain in irritable bowel syndrome (IBS). FODMAPs, are poorly digested carbohydrates and removing FODMAPs from the diet relieves abdominal pain in approximately half of IBS patients. Unfortunately, FODMAPs are contained in many foods, which makes it challenging for patients to remain on a low FODMAP diet for extended periods. Our proposed research will identify which subtypes of FODMAPs are most responsible for increasing pain and will tease apart whether the pain-causing effects of FODMAPs rely on the gut microbiota or not. To identify which specific type of FODMAP causes pain, IBS patients will adopt a low FODMAP diet and then individual FODMAP subtypes will be added back to their diet while monitoring changes to their pain. Stool samples will be collected from the participants to determine whether the composition of the gut microbiota or the chemicals that it produces are changed when symptoms are improved or exacerbated by manipulating FODMAP availability. In parallel studies, the microbiota of each IBS patient will be grown in specialized conditions to mimic the environment of the gut. These patient microbial communities will be exposed to the same FODMAP manipulations as the patients themselves experience. This will allow us to test whether the changes in gut microbiota composition and the chemicals produced that occur in IBS patients in response to FODMAP manipulations also occur when only the microbiota is exposed to these manipulations. Together, these studies will aim to optimize a dietary therapy for a common chronic pain condition and will provide novel insights into how diet affects the chemicals the gut microbiota produces that contribute to abdominal pain.

Inclusion Criteria:

• Adults aged 18-70 with IBS (Rome IV (now V) criteria)
• PROMIS belly pain score >12

Exclusion Criteria:

1. Concurrent significant organic GI pathology (i.e. celiac, IBD, etc.) as some symptoms may be related to their disease and not IBS.
2. Concurrent systemic disease and/or laboratory abnormalities considered by investigators to be risky or that could interfere with data collection.
3. Major gastrointestinal surgery (e.g. Roux en y, bowel resection) as symptoms may be related to previous surgery rather than IBS.
4. Body mass index above 30 kg/m2 as it is known how mediators in the GI tract that may be involved in pain signaling in the gut are affected by obesity.
5. History of active cancer in the last 5 years, other than basal cell cancer as the treatment may have impacted the GI tract.
6. Pregnant or breastfeeding women.
7. Active or recent participation (< 1 month) in a clinical study.
8. Use of antibiotics, probiotics, during, or one month prior to the study as may affect gut microbiota.
9. Use of new medications less than 4 weeks prior to the study as may alter gut microbiota and/or IBS symptoms.
10. Allergies to any of the ingredients used in the study.
11. Any immune-compromising conditions as may affect GI symptoms.
12. Currently being treated for eating disorder, schizophrenia, psychosis or other acute mental disorders as participating in a diet challenge study may have negative impact on these disorders.