In early 2026, the Rome V consensus redrew the map of irritable bowel syndrome. For a decade, the Rome IV criteria excluded millions of people whose symptoms did not fit the right box. The overly strict pain threshold had caused global IBS prevalence to drop from 9.2% to 3.8%. Many patients lived with real bloating, disturbed bowel habits and fatigue, without ever receiving a clear answer.

Rome V corrects this imbalance. The new criteria reintegrate real clinical presentations, restore diagnostic sensitivity to 90.2%, and draw on a decade of discoveries about the gut-brain axis: post-infectious autoimmunity, mucosal immunity, small intestinal bacterial overgrowth. IBS is no longer a diagnosis of exclusion made by default. It is a positive diagnosis, with identifiable mechanisms and precise therapeutic levers.

Our promise at Diaeta: nutritional support grounded in these scientific advances to restore your digestive comfort — without ever leaving you hungry and while keeping foods you find delicious. IBS is manageable, and it is managed on your terms.

1. Rome V: What Changes in IBS Diagnosis

IBS belongs to the family of disorders of gut-brain interaction. The Rome committee revises its criteria every ten years. Rome IV, published in 2016, raised the threshold for abdominal pain to at least one day per week and removed the term "discomfort", considered too imprecise across languages. This choice paid off in specificity — 97.1% — but sacrificed sensitivity.

1.1 The prevalence paradox

By tightening the pain criterion, Rome IV made genuinely ill patients disappear from the statistics. Global IBS prevalence fell from 9.2% (Rome III) to 3.8% (Rome IV). The effect hit Asia hardest, where patients describe their symptoms through bloating and discomfort more than acute pain. In Japan, estimated prevalence dropped from 9.3% to 2.2%. In China, from 7.4% to 2.3%.

1.2 The new Rome V threshold

Rome V relaxes the pain frequency criterion: at least 3 days per month on average, versus at least 1 day per week. Prospective validation trials show this threshold restores sensitivity of 90.2% while maintaining specificity of 85.1%. Global prevalence is expected to rise back towards 9%.

Criterion	Rome IV (2016)	Rome V (2026)
Pain frequency	≥ 1 day / week	≥ 3 days / month (average)
Chronicity	≥ 6 months	≥ 6 months (unchanged)
Association with defaecation	2 of 3 criteria	2 of 3 criteria (unchanged)
Global prevalence	3.8%	~9% expected

1.3 Subtypes and continuum with chronic constipation

Rome V retains the four subtypes: IBS-C (constipation), IBS-D (diarrhoea), IBS-M (mixed) and IBS-U (unclassified). The novelty lies in the recognition of fluid transitions between these forms: the same patient may shift from IBS-D to IBS-M over months. The consensus also places IBS-C and chronic constipation on a single spectrum of sensorimotor dysfunction, aligning their management.

1.4 Paediatrics: from age criteria to symptom patterns

Rome V abandons age-based subdivisions in favour of a framework based on symptom patterns by anatomical region. "Infantile colic" becomes "infant distress syndrome". The consensus identifies developmental risk factors: early digestive infections, food allergies, stress, adverse childhood experiences. These interact with vulnerability of the autonomic nervous system.

Key insight: If Rome IV excluded you from diagnosis for insufficient pain frequency, Rome V brings you back within its scope. Your bloating and disturbed bowel habits are recognised as IBS symptoms, not as a complaint without a name.

2. Pathophysiology: Post-Infectious Autoimmunity

Food poisoning can trigger lasting IBS. Approximately 11% of people develop post-infectious IBS after acute bacterial gastroenteritis. Research has elucidated the molecular cascade linking infection to the chronic disorder.

2.1 The molecular mimicry cascade

Four pathogenic bacteria play a central role: Campylobacter, Salmonella, E. coli, Shigella and Yersinia. They release a toxin, CdtB (Cytolethal Distending Toxin B). The immune system produces anti-CdtB antibodies to neutralise this toxin.

The problem lies in the structural resemblance between CdtB and vinculin, a cytoskeletal protein present in the enteric nervous system, smooth muscle and interstitial cells of Cajal. These cells orchestrate the migrating motor complex, the "broom" that clears the small intestine between meals. Through cross-reactivity, anti-CdtB antibodies attack vinculin. The autoimmunity damages pacemaker cells, disrupts the migrating motor complex, and promotes luminal stasis, SIBO, gas and visceral pain.

2.2 The second-generation IBS-Smart test

Serology measures two antibodies — anti-CdtB and anti-vinculin — and guides the clinician.

Serological profile	Specificity / PPV	Interpretation
Anti-CdtB+ / Anti-vinculin−	94% / 96%	Recent or past gastroenteritis, high SIBO risk
Anti-CdtB− / Anti-vinculin+	91% / 96%	Self-sustaining chronic autoimmune state (3 to 4 months to establish)
Anti-CdtB+ / Anti-vinculin+	100% / 100%	Active high-titre autoimmunity, recent infection, maximum SIBO risk
Anti-CdtB− / Anti-vinculin−	Non-indicative	Investigate coeliac disease, bile acid malabsorption, microscopic colitis

The Wellmark 2026 assessment classifies this serological test as "investigational": no randomised trial proves that screening improves long-term prognosis compared to symptom-based Rome V management. Its utility lies in therapeutic orientation and validation of the patient's experience. Putting a mechanism to symptoms changes the therapeutic relationship.

2.3 Mucosal barrier and low-grade inflammation

Mucosal biopsies by Nicholas Talley identify low-grade inflammation and intestinal hyperpermeability as central drivers. Food allergens and infections create micro-epithelial tears. Antigens cross the barrier, trigger cytokine cascades, recruit mast cells and eosinophils. These cells release histamine and tryptase, which sensitise sub-mucosal nerve endings. The result: visceral hypersensitivity, bloating, hypermotility.

Key insight: If your digestive problems began after food poisoning or gastroenteritis, the post-infectious autoimmune mechanism probably explains your situation. This pathway directly guides the management strategy.

3. Microbiome: The SIBO, IMO, SIFO Spectrum

IBS frequently accompanies a microbial imbalance in the small intestine. The umbrella term SIMO groups three distinct forms, each with its organism and clinical profile.

Form	Organism / gas	Clinical profile
Hydrogen SIBO	Bacteria, H₂	Rapid carbohydrate fermentation, luminal water retention, diarrhoea, cramps
IMO (methanogens)	Methanobrevibacter smithii, CH₄	Methane inhibits cholinergic transmission, severe constipation
H₂S overproduction	Sulphate-reducing bacteria, H₂S	Rapid transit, visceral hypersensitivity, sulphurous gas
SIFO (fungal)	Yeasts (Candida)	Symptoms similar to SIBO, undetectable on breath test

3.1 Consequences of massive overgrowth

A high microbial load depletes the body: vitamin B₁₂ deficiency, carbohydrate malabsorption, micro- or macrocytic anaemia, chronic fatigue, polyneuropathy, concentration difficulties. Your doctor and dietitian look for these signs in your workup.

Key insight: A breath test measuring only hydrogen and methane may miss hydrogen sulphide overproduction or fungal overgrowth. If your symptoms persist despite a "normal" test, the trail remains open.

4. IBS or IBD: A Critical Distinction

IBS and inflammatory bowel diseases (IBD: Crohn's disease, ulcerative colitis) share symptoms but rest on different mechanisms. American Gastroenterological Association guidelines distinguish them clearly.

Dimension	IBS	IBD
Microbiome	Luminal dysbiosis, altered SCFAs, H₂, CH₄	Reduced alpha diversity, Firmicutes depletion, adherent-invasive E. coli
Cellular target	Cajal cells, enteric neurones, sub-mucosal mast cells	Paneth cell dysfunction, intraepithelial lymphocytes
Validated approach	Rifaximin + low-FODMAP diet	VSL#3 reserved for pouchitis prevention (ulcerative colitis)

4.1 Faecal microbiota transplantation

The European SoHO 2024 regulation restricts faecal microbiota transplantation to recurrent Clostridioides difficile infections. OpenBiome suspended general distribution at the end of 2024 under FDA requirements. Faecal transplantation is therefore not a routine option for IBS.

5. 2026 Medical Treatments

Medical treatments fall within your doctor's remit. Understanding how they work helps you engage with your clinician and coordinate your nutritional management.

5.1 Linaclotide (Linzess/Constella) for IBS-C

Linaclotide is a 14-amino-acid peptide, a GC-C receptor agonist on the luminal membrane of enterocytes. It stimulates intracellular cGMP, activates the CFTR channel, induces chloride and bicarbonate secretion, and water follows by osmosis. Transit accelerates. Extracellular cGMP also suppresses afferent visceral nociceptors, providing lasting pain relief.

2024 data show that 34% of IBS-C patients meet the FDA response criteria (≥30% pain reduction and at least 3 additional complete spontaneous bowel movements per week), versus 14% on placebo. Maximum abdominal pain decreases by an average of 45% at week twelve. Dosage: 290 µg per day, 30 minutes before the first meal. Severe diarrhoea in approximately 2%. Approved in children aged 6 to 17 for functional constipation; contraindicated under 6 years (risk of severe dehydration).

5.2 Tenapanor (Ibsrela) for refractory IBS-C

Tenapanor inaugurates a new class: inhibition of the sodium-hydrogen exchanger NHE3. It blocks apical sodium absorption, retains sodium in the lumen, draws in water, increases fluid volume and stimulates peristalsis. By modifying luminal pH, it promotes mucosal healing and stabilises tight junctions, reducing low-grade inflammation and visceral pain.

The TANDEM trials show lasting improvement in stool frequency and abdominal pain. Dosage: 50 mg twice daily, just before breakfast and dinner. Approved in adults with IBS-C refractory to laxatives and fibre. Contraindicated under 6 years; to be avoided from 6 to 17 years.

5.3 Hyoscyamine (IBStat) for acute pain

Hyoscyamine is a fast-acting liquid antispasmodic, suited to acute pain crises in IBS-D and IBS-M. The liquid is rapidly absorbed through the buccal and gastric mucosa. It is a competitive antagonist of M3 muscarinic receptors, blocking smooth muscle spasm and reducing cramps within 30 minutes. Individualised on-demand dosing, in drops or sublingual solution. Caution with anticholinergic effects: risk of heat stroke, acute angle-closure glaucoma.

5.4 Reference agents

PEG 3350: 17 g once daily, first-line osmotic laxative for constipation
Prucalopride: 2 mg once daily, 5-HT₄ agonist, for refractory chronic constipation

Key insight: None of these medications replace the nutritional approach. They work better when your diet supports your transit and comfort. Doctor and dietitian work together.

6. Nutrition: FODMAP, Fibre and PHGG

Diet remains the most powerful and lasting lever in IBS. Conducted properly, it deprives you of nothing: it identifies your triggers and rebuilds a varied, enjoyable plate.

6.1 The three-phase FODMAP approach

The low-FODMAP diet unfolds in three stages — never as permanent elimination.

Reduction phase (2 to 6 weeks): temporary reduction in fermentable carbohydrates to calm symptoms
Structured reintroduction phase: methodical testing by FODMAP group to identify your precise triggers
Personalisation phase: an expanded, liberalised plan tailored to your individual tolerance

Prolonged strict elimination markedly reduces protective Bifidobacterium. The reintroduction phase is not optional: it protects your microbiome and quality of life.

6.2 Soluble fibre, not insoluble

Aim for 20 to 30 g of soluble fibre per day. Psyllium (ispaghula) binds water and improves stool consistency in both IBS-C and IBS-D. Insoluble fibres such as wheat bran ferment rapidly and irregularly: they worsen gas, bloating and pain. A critical distinction that many generic recommendations overlook.

6.3 Partially hydrolysed guar gum (PHGG)

PHGG at 6 g per day for 12 weeks significantly improves bloating and flatulence compared to placebo. The benefit persists up to 4 weeks after stopping. This gentle prebiotic fibre suits sensitive intestines that tolerate other fibres poorly.

Key insight: The distinction between soluble and insoluble fibre changes everything. Increasing "fibre" without this nuance can worsen your symptoms. Psyllium and PHGG soothe; wheat bran can irritate.

7. Probiotics: Strains with Evidence

A probiotic acts only at the strain, dose and indication studied. Random selection leads to failure. The following strains have solid clinical data in IBS.

Strain	Indication	Dose and duration
Bifidobacterium longum 35624	IBS-D / IBS-M	10⁹–10¹⁰ cells/day, 4 to 8 weeks
Lactobacillus rhamnosus GG	Children and adults	6×10⁹–4×10¹⁰ cells/day
Lactiplantibacillus plantarum 299v	Visceral pain, flatulence	10¹⁰–5×10¹⁰ cells/day
Saccharomyces cerevisiae CNCM I-3856	IBS-C, bloating	4×10⁹–8×10⁹ cells/day, 8 to 12 weeks
Bacillus coagulans IS2	Children and adults (pain, quality of life)	2×10⁹ cells/day, 8 weeks
Bacillus coagulans MTCC5856	Global IBS-D	2×10⁹ cells/day, 90 days

Meta-analyses confirm that B. longum 35624 improves pain, bloating and global scores. L. plantarum 299v reduces flatulence, pain and colonic distension. S. cerevisiae CNCM I-3856 exerts a local analgesic effect. A Swedish double-blind trial (NCT07584278, n=252, Rome V criteria, IBS-SSS ≥75, 12 weeks) has been under way since April 2026 and will further refine these recommendations.

Key insight: "Taking probiotics" means nothing without specifying the strain. The same species may help one patient and have no effect on another. Selection is based on your IBS subtype and dominant symptom.

8. Gut-Brain Axis Therapies

IBS is a disorder of gut-brain interaction. Acting on the brain genuinely modifies the gut. These approaches do not claim "it's all in your head": they target a measurable neurobiological circuit.

8.1 Cognitive behavioural therapy (CBT)

Meta-analyses place the odds of symptom persistence at around 0.6 compared to usual care. CBT delivers lasting improvements in severity and quality of life. It acts on visceral hypervigilance and stress reactions that perpetuate symptoms.

8.2 Gut-directed hypnotherapy

Gut-directed hypnotherapy achieves 70 to 80% responders in refractory IBS, with benefits lasting years after treatment. It normalises colonic motility and attenuates central processing of sensory signals. One of the best-validated interventions for resistant forms.

8.3 Digital therapeutics

Software programmes (Regulora, Zemedy) deliver CBT and hypnotherapy remotely. They widen access, without erasing the disparities affecting low-income, rural or minority populations. A complementary tool, not a substitute for human support.

8.4 Non-invasive vagal stimulation

Vagus nerve stimulation activates the anti-inflammatory cholinergic pathway via the α7 nicotinic receptor. It curbs TNF-α and IL-6 production, attenuates visceral hypersensitivity, stimulates colonic motility and promotes Bifidobacterium and Blautia. An emerging avenue directly linking the nervous system, inflammation and microbiome.

Key insight: The gut-brain axis is not a metaphor. Gut-directed hypnotherapy produces measurable changes in colonic motility. IBS treatment addresses body and nervous system together.

9. A Structured Care Pathway

Rome V enables a clear diagnostic and therapeutic pathway, from positive diagnosis to targeted treatment.

Positive Rome V diagnosis: pain at least 3 days per month, absence of alarm features
IBS-D or IBS-M: IBS-Smart serology (anti-CdtB, anti-vinculin). Positive result confirms post-infectious IBS and directs towards SIBO treatment (rifaximin, PHGG). Negative result prompts investigation for bile acid malabsorption, coeliac disease, microscopic colitis
IBS-C: first-line PEG or prucalopride. If unsuccessful, linaclotide 290 µg/day or tenapanor 50 mg twice daily
For all subtypes: soluble fibre (PHGG, psyllium), probiotics matched to subtype, gut-directed hypnotherapy or digital therapeutic

9.1 Remote monitoring

Digital monitoring of IBS is developing rapidly. Platforms combine remote symptom tracking with hybrid digital and in-person support. This trend sustains long-term management without replacing the relationship with your clinician.

10. Our Personalised Approach at Diaeta

At Diaeta, we treat IBS for what it is: a real, measurable disorder that responds to a tailored strategy. Rome V criteria recognise you. Our support restores your comfort, meal by meal.

What We Promise You

Never hungry: even during the FODMAP reduction phase, your meals satisfy. We build complete menus, not lists of prohibited foods
No unnecessary elimination: every adaptation is targeted and temporary. The reintroduction phase protects your microbiome and your enjoyment of eating
Evidence-based guidance: we apply Rome V criteria and 2026 data, not dietary trends
Personalised strategies: your IBS subtype, your triggers and your microbiome guide every recommendation

How We Support You

Comprehensive assessment: analysis of your symptoms, subtype, infectious history and test results
Three-phase FODMAP protocol: reduction, methodical reintroduction, personalisation — led by a Monash-certified specialist
Targeted fibre and probiotic selection: psyllium, PHGG and strains matched to your profile
Medical coordination: alignment of nutrition with your doctor's treatment and hypnotherapy where needed

Outcomes Observed

With our personalised approach, patients typically report:

Lasting reduction in bloating and pain through identification of their real triggers
Regulated bowel habits through a strategy matched to their subtype
Return of enjoyment in eating without fear of the next meal

You are living with chronic digestive symptoms and want management grounded in Rome V criteria? Book a personalised consultation in Brussels. Together, we will build your tailored nutritional plan.

Scientific References

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Sperber AD, Bangdiwala SI, Drossman DA, et al. Worldwide Prevalence and Burden of Functional Gastrointestinal Disorders. Gastroenterology. 2021;160(1):99-114.
Pimentel M, Morales W, Rezaie A, et al. Development and Validation of a Biomarker for Diarrhea-Predominant Irritable Bowel Syndrome in Human Subjects. PLoS One. 2015;10(5):e0126438.
Talley NJ, Walker MM, Holtmann G. Functional dyspepsia and the gut-brain axis: low-grade duodenal inflammation. Lancet Gastroenterol Hepatol. 2018;3(4):252-262.
Pimentel M, Saad RJ, Long MD, Rao SSC. ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. Am J Gastroenterol. 2020;115(2):165-178.
Singer-Englar T, Rezaie A, Pimentel M. Competitive hydrogen and methane utilization by gut microorganisms. Dig Dis Sci. 2023;68:263-272.
Lacy BE, Pimentel M, Brenner DM, et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2021;116(1):17-44.
Chey WD, Lembo AJ, Rosenbaum DP. Efficacy of Tenapanor in Treating Patients With Constipation-Predominant IBS: TANDEM Trials. Am J Gastroenterol. 2020;115(2):281-293.
Rao SSC, Quigley EMM, Shiff SJ, et al. Effect of Linaclotide on Severe Abdominal Pain in Patients With IBS-C. Clin Gastroenterol Hepatol. 2014;12(4):616-623.
Halmos EP, Power VA, Shepherd SJ, et al. A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology. 2014;146(1):67-75.
Niv E, Halak A, Tiommny E, et al. Randomized clinical study: partially hydrolyzed guar gum (PHGG) versus placebo in IBS. Nutr Metab. 2016;13:10.
Whorwell PJ, Altringer L, Morel J, et al. Efficacy of an encapsulated probiotic Bifidobacterium infantis 35624 in women with IBS. Am J Gastroenterol. 2006;101(7):1581-1590.
Ducrotté P, Sawant P, Jayanthi V. Clinical trial: Lactobacillus plantarum 299v in irritable bowel syndrome. World J Gastroenterol. 2012;18(30):4012-4018.
Ford AC, Lacy BE, Harris LA, et al. Effect of Antidepressants and Psychological Therapies in IBS: Systematic Review and Meta-analysis. Am J Gastroenterol. 2019;114(1):21-39.
Peters SL, Yao CK, Philpott H, et al. Gut-directed hypnotherapy and the low FODMAP diet in IBS. Aliment Pharmacol Ther. 2016;44(5):447-459.

Irritable Bowel Syndrome: Rome V Criteria and Treatment in 2026