Dietary Triggers of Gastrointestinal Symptoms in IBS Patients

Number of participants with a clinically meaningful worsening of symptoms during dietary challenge compared to sham, as defined by an increase of >50 points in the Irritable Bowel Syndrome Symptom Severity Score (IBS-SSS). The IBS-SSS ranges from 0 to 500, with higher scores indicating greater symptom severity. A >50-point increase is considered a clinically significant worsening.

Worsening of general gastrointestinal symptoms (using The Patient-Reported Outcomes Measurement Information System (PROMIS Scales) for belly pain, diarrhea, constipation, or gas & bloating) after dietary challenge compared to sham. Scores are calculated using the Scoring Service by Health Measures and range from 20-80, with medians set at 50 and a standard deviation of 10. Higher scores indicate greater symptom severity. Four PROMIS subscales are being used: Gas & Bloating, Diarrhea, Constipation, and Belly Pain. Each subscale follows the T-scale scoring range of 20-80 and will be measured independently.

Colonic transit assessed by SHAPE study (radiopaque markers).

We measured orocecal transit time according to a modified SHAPE study using radiopaque markers, clinically used to identify patients with colonic inertia. Participants consumed 1 SITZARKS capsule (Konsyl Pharmaceuticals, Easton, MD) containing 24 markers, 48 hours prior to a plain abdominal film. A technician took a plain abdominal x-ray to provide images of the number and locations of the markers remaining in the gastrointestinal tract at 48 hours. A greater number of markers (up to 24) indicates slower gastrointestinal transit while less markers (or none) indicate faster transit.

The outcome was assessed at the end of each 1-week intervention period (i.e., at Week 1 for Sham, Gluten, and Wheat Arms). Due to the COVID-19 pandemic, in-person study visits were limited and the SHAPE study was only conducted in N=13 participants.

Change in AGA levels after purified gluten and whole wheat (gluten+wheat ATI) challenge will be assessed by ELISA

NOTE: Due to the COVID-19 pandemic, in-person, non-essential blood withdrawals were paused. Blood collection occurred pre-pandemic and after in-person visits were allowed, in a total of N=14 participants. A post-study follow-up amendment, accepted by the Hamilton integrated Research Ethics Board (HiREB), allowed post-study collection of blood samples to assess the presence of AGAs and genetic markers.

This outcome was intended to assess gut microbiota profiles using 16S rRNA Illumina sequencing of stool samples collected after each 1-week intervention period. However, data for this outcome are not available.

Patient HLADQ2/8 status will be assessed at baseline

NOTE: Due to the COVID-19 pandemic, in-person, non-essential blood withdrawals were paused. Blood collection occurred pre-pandemic and after in-person visits were allowed, in a total of N=14 participants. A post-study follow-up, accepted by the Hamilton integrated Research Ethics Board (HiREB), allowed post-study collection of blood samples to assess the presence of AGAs and genetic markers.

Worsening of depression, anxiety, and stress sub-scales during dietary challenge was assessed by Depression Anxiety Stress Scale (DASS-21). The DASS-21 has 21 questions. The three subscales (depression, anxiety, and stress) are reported independently and range from 0 to 42, with higher scores indicating greater symptom severity.

Worsening of somatic symptoms like fatigue, sleeping trouble, and pain were assessed using Patient Health Questionnaire (PHQ-15). Scores range from 0 to 30, with greater scores indicating greater severity.

Stool consistency was assessed by Bristol Stool Scale. Types 1 and 2 indicate harder stools, types 3, 4, and 5 are normal, and types 6 and 7 indicate runnier, more liquid stool.

Presence of gluten in stool samples was assessed to evaluate dietary compliance using an ELISA for gluten immunogenic peptides (GIP), measured in micrograms per gram of stool (μg/g).

Stool samples were collected at the end of each 1-week intervention period (i.e., at Week 1 for Sham, Gluten, and Wheat). The values reported reflect GIP concentration at the end of each intervention.

This outcome was intended to assess dietary intake and compliance during each 1-week intervention period using the MealLogger app. Participants were instructed to take pictures of all meals during each intervention week to support dietary tracking and adherence monitoring. However, image analysis was not performed and data for this outcome are not available.

Evaluates symptom duration at the end of the diet challenge using the IBS-SSS. The overall score ranges from 0-500 in total, with each of the 5 questions ranging from 0 to 100. A higher score indicates higher symptom severity and the total score is summed.

This outcome was intended to assess changes in pro-inflammatory cytokines (TNF-α, IL-8, and IFN-γ) using ex vivo peripheral blood mononuclear cell (PBMC) stimulation in a subset of participants. Blood was collected at baseline and after each 1-week dietary intervention (Sham, Gluten, and Wheat) to isolate PBMCs. However, due to the COVID-19 pandemic and the limited clinical phenotype observed, PBMC samples (N=11) were not analyzed. No outcome data are available.

At study completion and unblinding, the researchers compiled the study results (ex., worsening in IBS symptoms after gluten challenge) and provided this information to study participants after their study completion. An expert interview-based gluten-free diet assessment used previously in the study was conducted with study participants immediately prior and one month after.

This amendment was approved by the Hamilton Ethics Board in June 2022 and was based on participant requests. We used the same gluten-free diet assessment as the primary study. We included new pre- and post-disclosure surveys to ask about current diet habits, beliefs surrounding wheat/gluten sensitivity, and how their behaviours would change after results disclosure.

At study completion and unblinding, the team compiled the study results (ex., worsening in IBS symptoms after challenges) and provided this information to participants. Previous study surveys were sent to participants immediately prior and 1 month after.

We used the following outcomes:

• IBS symptoms: IBS Symptom Severity Score (IBS-SSS, range=[0, 500], higher score=worse symptoms)
• General gastrointestinal symptoms: Patient-Reported Outcomes Measurement Information System (PROMIS) sub-scales for abdominal pain, diarrhea, constipation, bloating & gas (each sub-scale has a range of 20-80 and higher scores=worse symptoms)
• Mood: Depression, Anxiety & Stress Scale (DASS21, each sub-score [depression/anxiety/stress] has a range of 0-42 and higher scores=worse symptoms)
• Somatic symptoms: Patient Health Questionnaire 15 (PHQ15), range=(0, 30), greater score=worse symptoms)

For greater detail, see above secondary outcome measure descriptions.

Worsening of IBS symptoms (using Irritable Bowel Syndrome Symptom Severity Score (IBS-SSS)) during dietary challenge compared to sham. The overall score ranges from 0-500 in total, with each of the 5 questions ranging from 0 to 100. A higher score indicates higher symptom severity and the total score is summed. An increase in >50 points indicates worsening of symptoms.