IBD vs functional gut disorders
Inflammatory bowel disease (IBD), Crohn’s disease and ulcerative colitis, is defined by chronic intestinal inflammation with mucosal injury visible on endoscopy and histology, plus biomarkers such as fecal calprotectin and CRP during active disease. Functional gut disorders, chiefly irritable bowel syndrome (IBS), are diagnosed by symptom criteria after alarm features are investigated (Rome IV). Both can present with pain, bloating, and erratic bowel habit; only IBD carries structural damage, flare risk, and immunosuppressive treatment pathways.
Consumer microbiome reports sit downstream of this distinction. Group-level IBD studies often show altered diversity and reduced butyrate-associated taxa (Sokol et al., 2008), but meta-analyses show no universal diversity reduction across diseases, diarrhoeal illness and IBD are among the clearer exceptions (Duvallet et al., 2017). A single stool panel cannot rule in or rule out IBD.
For report routing: Reading your microbiome report. For inflammation testing: Gut inflammation markers.
What not to conclude
| Report or narrative | Weak conclusion | More accurate framing |
|---|---|---|
| ”Dysbiosis” flag | Hidden IBD | Non-specific; calprotectin + clinical assessment |
| Low Faecalibacterium | Ulcerative colitis | Association in cohorts; also seen in IBS and healthy |
| Sequencing inflammation score high | Mucosal flare | Not validated like calprotectin |
| Normal microbiome report | No IBD | Quiescent IBD can have normalised stool composition |
| IBS diagnosis | Never develop IBD | Overlap syndromes exist; new red flags need re-evaluation |
| FMT or cleanse from kit | IBD alternative | IBD is specialist-managed; FMT indications are narrow |
Clinical distinction, inflammation vs function
| Feature | IBD (Crohn’s / UC) | Functional (e.g. IBS) |
|---|---|---|
| Mucosal inflammation | Present on endoscopy/biopsy | Absent after adequate workup |
| Calprotectin | Often elevated in active disease | Usually normal (<50–100 µg/g lab-dependent) |
| Blood in stool | Common in flares | Alarm feature, investigate |
| Nocturnal diarrhea | Suggests organic disease | Alarm feature |
| Weight loss, fever | Concerning for IBD | Alarm feature |
| Treatment backbone | Anti-inflammatory / immunomodulator | Diet, motility agents, neuromodulators, selected probiotics |
| Cancer surveillance | Colonoscopy schedule | Routine screening per age/risk only |
IBS subtypes (IBS subtypes) do not map to IBD subtypes. Post-infectious IBS can follow gastroenteritis without persistent IBD (Post-infectious IBS).
When microbiome testing helps vs distracts
May add context (never alone):
- Research-oriented curiosity after established IBD diagnosis and stable management
- Comparing same-lab samples before/after approved therapy in a trial setting
- Discussing diet–microbiome hypotheses with a gastroenterologist
Distracts or harms when:
- Alarm features unexplained, sequencing delays calprotectin, celiac serology, colonoscopy
- Report drives unproven supplement stacks during active flare
- “Heal dysbiosis” narrative replaces prescribed immunotherapy
- Consumer opportunistic pathogen lists trigger anxiety without culture context
Tier calprotectin and clinical assessment above sequencing “inflammation scores” every time.
Shared symptoms, bloating, pain, altered habit
| Symptom | IBD considerations | Functional considerations |
|---|---|---|
| Bloating | Stricture, bacterial overgrowth in Crohn’s, active inflammation | Visceral hypersensitivity, FODMAP fermentation, dyssynergia (Bloating) |
| Pain | Inflammatory, fistulising, or obstructive | Rome criteria-related; neuropathic components |
| Diarrhea | Active UC flare, Crohn’s disease of small bowel | IBS-D, bile acid malabsorption, PI-IBS |
| Constipation | Stricture, proctitis | IBS-C, pelvic floor dysfunction |
Visible distension without increased gas volume occurs in functional disorders (Villoria et al., 2011), a pattern sequencing does not detect.
Diet and microbiome narratives in IBD
Exclusive enteral nutrition and defined exclusion diets have trial evidence in paediatric Crohn’s and selected adult protocols, always specialist-supervised, not extrapolated from consumer “avoid these taxa” lists.
Butyrate producer abundance (Faecalibacterium, Roseburia) correlates with healthier mucosa in some UC remission studies (Lopez-Siles et al., 2018), association, not proof that oral butyrate or generic probiotics induce remission. Ulcerative colitis management hinges on mucosal healing on endoscopy, not pathway scores.
Low microbiota-accessible carbohydrate intake may reduce substrate for commensal fermentation, relevant context for diet advice, not a replacement for anti-inflammatory drugs in active IBD.
What to do next
- Red flags present → clinical pathway first (Red flags).
- Persistent symptoms with normal basic labs → discuss calprotectin, celiac serology, and whether colonoscopy is indicated.
- Established IBD → treat inflammation per guideline; use consumer sequencing only as optional context.
- Report shows low butyrate producers → do not override gastroenterology plan; see SCFAs.