Probiotics and Biomarkers in Irritable Bowel Syndrome

The BIO-IBS study is a double-blind, randomized, placebo-controlled clinical trial investigating whether a combination probiotic improves symptoms in adults with irritable bowel syndrome (IBS). The trial also explores biological mechanisms and predictors of treatment response.

Background & Rationale IBS is a common disorder of gut-brain interaction (~4% prevalence in Sweden). Current treatments include dietary, pharmacological, and psychological approaches. Increasing evidence suggests the gut microbiome plays a key role, prompting interest in probiotics.

Aims

• Evaluate effect of probiotic combination on IBS symptoms. 2, Identify predictors of response. 3. Investigate IBS pathophysiology and biomarkers.

Study Design

Type: Double-blind, randomized, placebo-controlled, parallel-group Participants: 252 adults with IBS Randomization: 1:1 (probiotic vs placebo) Treatment duration: 12 weeks Follow-up: 3 months post-treatment Timeline: Recruitment starting April 2026 lasting ~3 years

Participants Inclusion Criteria

Adult (≥18 years), IBS (Rome IV criteria) IBS-SSS > 75 BMI 18.5-35 Able to consent and complete Swedish questionnaires

Key Exclusion Criteria

Significant gastrointestinal or systemic disease Recent antibiotics (within 3 months) or probiotics (within 2 weeks) Opioid use Pregnancy/breastfeeding Significant lab abnormalities (e.g., high fecal calprotectin) Major lifestyle/treatment changes

Intervention

Active treatment: Tablet containing both L. reuteri strains Placebo: Identical without bacteria Dose: 1 tablet twice daily Duration: 12 weeks Compliance ≥80% required for per-protocol analysis.

Outcomes Primary Outcome

Change in IBS symptom severity (IBS-SSS) from baseline to 12 weeks (intervention vs placebo)

Secondary Outcomes

Proportion achieving ≥50 or ≥100 point IBS-SSS reduction Gastrointestinal symptoms (GSRS-IBS) Pain reduction Quality of life (IBSQOL) Work productivity (WPAI:IBS) Transit time (gut motility) Adverse events Sustainability of effects (3-month follow-up)

Exploratory Outcomes

Stool consistency/frequency Biomarkers (microbiome, immune, metabolomics, etc.) Psychological and lifestyle factors Dietary influences Mechanistic insights into IBS

Study Procedures Visits Screening (2-8 weeks before randomization Consent, questionnaires, biological samples, diaries

Randomization (Day 0) Baseline assessments and start of treatment

During intervention Regular symptom tracking Phone follow-up at week 6

End of treatment (12 weeks) Repeat assessments and samples

Follow-up (3 months later) Long-term outcomes

Optional (Facultative) Assessments Rectal sensitivity (barostat) Sigmoidoscopy ± confocal endomicroscopy MRI (motility and colonic volume)

Measurements

Questionnaires: IBS-SSS, GSRS-IBS, HADS, PHQ-15, IBSQOL, stress, work productivity Biological samples: blood, stool, urine, saliva Gut function: transit time (radiopaque markers and sweetcorn method) Diet: food frequency and recall diaries

Statistical Considerations Sample size: 252 participants (powered to detect clinically meaningful IBS-SSS difference)

Populations:

Intention-to-treat (all randomized) Per-protocol (≥80% compliance, no major deviations) Analysis plan: Defined in a Statistical Analysis Plan No interim analysis

Safety Probiotics considered safe with minimal risk (mainly transient flatulence). Adverse events will be recorded and classified by severity and causality. IBS symptom fluctuations are not counted as adverse events unless worsened.

Ethics & Data Handling Conducted according to Declaration of Helsinki and ICH-GCP. Participants give informed consent and can withdraw anytime. Data are pseudonymized and securely stored (REDCap)

Risk-Benefit Assessment Low risk due to established safety of L. reuteri strains Moderate participant burden (questionnaires, sample collection) Optional procedures may cause discomfort but are controlled and voluntary Potential benefit: improved IBS symptoms and better understanding of disease mechanisms

Key Strengths Large sample size Rigorous randomized controlled design Comprehensive symptom, biological, and mechanistic assessment Long follow-up

Conclusion This study aims to determine whether a novel probiotic combination improves IBS symptoms and to identify biological and clinical predictors of response, contributing to more personalized treatment strategies in IBS.

Inclusion criteria

• Diagnosed with IBS according to ROME V criteria
• IBS-SSS greater than or equal to 75
• Adult over 18 years old
• BMI 18.5-35 kg/m2
• Able to understand the participant information sheet and willing to comply with the study protocol
• Able to give informed consent
• Able to complete the Swedish questionnaires

Exclusion criteria

• History of any gastroenterology disease including coeliac disease, heart, liver, neurological, or current psychiatric disease, diabetes, any surgery to the abdomen that affects intestinal function (not including cholecystectomy, appendectomy, ceasarean section).
• The use of opioids 1 month prior to screening and throughout the study
• The use of probiotic supplements from 14days before randomization and during the study (not including foods with probiotic components)
• Consumption of antibiotics 3 months prior to screening and throughout the study
• The start of any new drugs that affect the gastrointestinal tract or symptoms within the last month before the start of the study. As well as the start of new diets of psychological therapy as treatment for IBS symptoms.
• Participation in any medical research during the last month
• Clinically relevant lab abnormalities at the time of screening (fecal calprotectin greater than or equal to 150 ug/g as absolute cutoff. If calprotectin is between 50 - 150ug/g the decision is made on clinical judgement)
• Pregnancy, plan to become pregnant during the study, breastfeeding
• alcohol consumption >14 units per week
• Use of recreational active drugs during 1 month before screening or during the study
• Use of medication that primarily affects bowel function, transit time, stool consistency 2 weeks before the intervention or during the 12 week intervention period