Note on terminology: "Irritable bowel disease" is not a standard medical term. You may be referring to Irritable Bowel Syndrome (IBS) — a functional GI disorder — or possibly Inflammatory Bowel Disease (IBD) (Crohn's disease and ulcerative colitis). This article covers IBS in full. IBD is a separate disease category covered briefly at the end.

Irritable Bowel Syndrome (IBS)

Definition

Epidemiology

• Global prevalence using Rome IV criteria: ~4.1–4.6%; higher with older (less restrictive) criteria
• More common in women (5.2%) than men (2.9%)
• Incidence: ~38 per 10,000 person-years
• Up to 50% of individuals with IBS symptoms never seek health care
• Generates ~4.4 million annual physician visits in the US
• Associated with significant comorbid somatic and psychological disorders, increased work absenteeism, and healthcare costs

Subtypes (Rome IV Classification)

Pathophysiology

1. Visceral hypersensitivity — lowered pain threshold to gut distension; a hallmark mechanism
2. Altered intestinal motility — colonic transit is slower in IBS-C and faster in IBS-D, though no single motor pattern is specific
3. Gut microbiota changes — altered composition and function
4. Mucosal immune activation — low-grade mucosal inflammation, increased mast cells
5. Autonomic nervous system dysregulation
6. CNS modulation changes — abnormal brain processing of visceral signals
7. Altered gut permeability (leaky gut)

• Genetic predisposition (family history increases risk 1.75–2.75×)
• Adverse childhood experiences
• Post-infectious IBS — gastroenteritis can trigger IBS in ~10% of cases (post-infectious IBS)
• Food triggers (e.g., fermentable carbohydrates — FODMAPs)
• Psychological stress

Diagnostic Criteria (Rome IV)

Recurrent abdominal pain, on average at least 1 day per week in the last 3 months, associated with ≥2 of:

1. Related to defecation
2. Associated with a change in frequency of stool
3. Associated with a change in form (appearance) of stool

Criteria fulfilled for the last 3 months with symptom onset ≥6 months before diagnosis.

"Red flag" features warranting further investigation:

• Age >50 at symptom onset
• Rectal bleeding
• Unintentional weight loss
• Nocturnal symptoms awakening from sleep
• Family history of colorectal cancer or IBD
• Abnormal physical examination or labs

Clinical Features

• Abdominal pain or discomfort — often crampy, relieved or worsened by defecation
• Bloating and distension — extremely common
• Altered bowel habits — diarrhea, constipation, or both; urgency, incomplete evacuation, mucus in stool
• Extraintestinal symptoms: fatigue, back pain, urinary symptoms, dyspareunia, headache
• Psychiatric comorbidities: anxiety and depression are highly prevalent

Diagnosis

• CBC, CRP/ESR (to exclude IBD/infection)
• Thyroid function tests (TSH)
• Celiac serology (anti-tTG IgA)
• Stool studies if diarrhea predominant (fecal calprotectin, ova/parasites, C. difficile)
• Colonoscopy if red flags present or age >45–50

Management

1. Lifestyle & Dietary Modifications

• Low-FODMAP diet: reduces fermentable oligosaccharides, disaccharides, monosaccharides, and polyols; effective in 50–70% of patients (strongest dietary evidence). A 2025 Lancet Gastroenterology network meta-analysis (PMID: 40258374) confirmed dietary interventions — especially low-FODMAP — as highly effective
• Regular exercise
• Avoidance of trigger foods (e.g., caffeine, alcohol, fatty meals)

2. Fiber

• Soluble fiber (psyllium/ispaghula) — modestly helpful especially in IBS-C
• Insoluble fiber (bran) — may worsen bloating/gas

3. Pharmacological Treatment

4. Gut Microbiota-Targeted Therapy

5. Psychological Therapies

• Cognitive behavioral therapy (CBT) — strong evidence, addresses the gut-brain axis
• Gut-directed hypnotherapy
• Mindfulness-based stress reduction

Prognosis

IBS vs. IBD — Key Distinctions