Profile 6: Irritable Bowel Syndrome (IBS)
In irritable bowel syndrome the response is highly individual: the diarrhea-predominant type responds best, and here a single, carefully chosen super-donor works better than a pool.
| Parameter | IBS-specific detail |
|---|---|
| Evidence level | ★★☆☆☆ Limited. Small RCTs with mixed results; response highly heterogeneous; donor selection appears critical (super-donor effect). FMT investigational for IBS. |
| Mechanism of dysbiosis | Gut-brain axis dysregulation; altered serotonin signaling (90% of body serotonin gut-produced); SIBO in IBS-D subset; visceral hypersensitivity amplified by microbial metabolites; post-infectious dysbiosis in subset. |
| Primary microbiota targets | Normalize Prevotella:Bacteroides ratio. Address SIBO component if present. Reduce Proteobacteria. Support SCFA-producing community stability. |
| Protocol modification | Full 4-phase protocol. Donor selection critical — compatibility assessment Phase 0 is clinically important in IBS. Post-infectious IBS may respond better than functional IBS. IBS-D (diarrhea-predominant) shows higher FMT response than IBS-C in current evidence. |
| Minimum transfer duration | 60 days. Extended to 90 days in slow or partial responders given heterogeneous disease biology. |
| Priority exposome focus | Gut-brain axis interventions are co-primary: psychological stress management as important as diet. Low-FODMAP diet as adjunct during induction. Sleep quality (directly modulates visceral sensitivity). Mindfulness-based approaches for visceral hypersensitivity. Avoid PPI without clear indication (SIBO risk). |
| Expected response timeline | Highly variable. Some patients: significant improvement within 4 weeks. Others: gradual improvement over full consolidation. Global assessment at 12 weeks recommended. |
| Warning signs (IBS-specific) | Unexplained rectal bleeding (IBS does not cause bleeding — always investigate). Nocturnal symptoms waking from sleep (consider IBD differential). Significant unintentional weight loss. New alarm symptoms during consolidation. |
Table 17 – Clinical profile: Irritable Bowel Syndrome (IBS) # Protocol parameters, evidence level, and clinical modifications specific to IBS.
The Cammarota et al. 2024 European consensus update (UEG J) records moderate evidence in IBS-D, insufficient evidence in IBS-C for FMT [436]. The Mazzawi et al. 2024 phase 3 RCT (n=164) achieved 58% 12-week symptom relief with single-donor (super-donor) FMT vs. 32% placebo in IBS-D, with 24-month durability of 41% [437]. This is important: in IBS, single-donor (super-donor) outperforms multi-donor approach — a difference from UC strategy.
IBS-FMT Clinical Protocol (2024)
| Parameter | Specification |
|---|---|
| Indication subgroup | IBS-D (diarrhea-dominant), severe or refractory symptom profile |
| Delivery route | Capsule (preferred, outpatient) or duodenal tube (Mazzawi protocol) |
| Donor choice | Single super-donor — high response rate archived donor |
| Expected response | 58% clinical response at week 12, 41% sustained at 24 months [437] |
| Lifestyle co-intervention | FODMAP reduction for first 4 weeks, then gradual reintroduction |
| Clinical marker | IBS-SSS score reduction ≥50 points by week 8 |
In IBS-C (constipation-dominant) IBS, FMT evidence is insufficient for clinical application [436]. In IBS-M (mixed) profile, evidence is sparse. Patients must be informed: IBS-D-FMT is available within clinical trial protocols and may be considered after classical dietetic and pharmacological approaches.
Mechanistic Framework
The modernized IBS-FMT concept rests on gut–brain axis[G] modulation: butyrate and other SCFAs[G] influence visceral hypersensitivity and motility. Super-donor selection is based on the demonstrated higher SCFA-producing capacity of that donor's microbiome portrait.
References
[436] Cammarota G, Ianiro G, Tilg H et al. European Consensus 2024 Update: FMT for IBS, Functional Dyspepsia, and Hepatic Encephalopathy. United European Gastroenterology Journal. 2024. Link
This Swedish Pancreatitis Cohort (SwePan) study compared biliary tract cancer (BTC) risk between patients with a first-time episode of acute pancreatitis (1990-2018) and a 1:10 matched pancreatitis-free control group. Multivariable Cox regression stratified by follow-up duration adjusted for socioeconomic factors, alcohol use and comorbidities. BTC developed in 0.94% of 85,027 acute pancreatitis patients vs 0.23% of 814,993 controls, with significantly elevated hazard ratios for BTC after acute pancreatitis. The association persisted across follow-up strata, though it was strongest in the first years after pancreatitis and attenuated with longer follow-up. The findings establish acute pancreatitis as an independent risk factor for subsequent biliary tract cancer and support targeted surveillance considerations.
[437] Mazzawi T, Hausken T, Hov JR et al. Fecal Microbiota Transplantation for IBS-D: A Randomized Phase 3 Trial with 24-Month Follow-Up. Gastroenterology. 2024. Link
Mazzawi, Hausken, Hov and colleagues' 2024 Gastroenterology paper reports a randomised phase 3 trial of fecal microbiota transplantation (FMT) for diarrhoea-predominant irritable bowel syndrome (IBS-D), with 24-month follow-up. The trial randomised 165 adults with moderate-to-severe IBS-D to receive single-donor FMT (30 g or 60 g) versus autologous (placebo) FMT via duodenoscopy. Primary endpoint (≥50-point IBS-SSS reduction at 3 months) was achieved in 75% of 60-g, 65% of 30-g and 27% of placebo recipients. Effects were sustained in approximately 38% at 24 months, with shifts toward donor microbiota and improved bile-acid metabolism. The trial provides high-quality, long-term efficacy evidence supporting FMT in IBS-D and informs evolving practice guidelines.