Irritable Bowel Syndrome (IBS) is one of the most common functional gastrointestinal disorders encountered in clinical practice, yet it remains a diagnosis of exclusion and often misunderstood. It affects 10-15% of the global population, disproportionately impacting quality of life while posing a diagnostic challenge due to symptom overlap with inflammatory bowel disease (IBD).

In this post, we’ll explore the pathophysiology, clinical features, diagnosis, and treatment of IBS with a special focus on dietary interventions (FODMAPs) and pharmacological options for IBS-C (constipation – predominant) and IBS-D (diarrhea- predominant) variants. We’ll also clarify key differences between IBS and IBD, a common source of confusion in clinical settings.

What is IBS?

IBS is chronic functional GI disorder characterized by recurrent abdominal pain associated with altered bowel habits, in the absence of any identifiable structural or biochemical cause.

Rome IV Criteria:

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

• Related to defection
• Change in frequency of stool
• Change in form (appearance) of stool

How to asses appearance of stool?

Use Bristol stool chart as shown below

Symptom onset must be at least 6 months before diagnosis.

IBS vs IBD: A common Confusion

Feature	IBS	IBD (Crohn’s /Ulcerative Colitis)
Nature	Functional disorder	Organic, inflammatory disease
Pathology	No mucosal inflammation or ulcers	Mucosal inflammation, ulceration
Colonoscopy	Normal	Abnormal (ulcers, erythema, pseudo-polyps)
Histology	Normal	Inflammatory infiltrates, granulomas
CRP/Fecal Calprotectin	Normal	Elevated
Red flag signs	Absent	May have blood in stool, weight loss
Risk of colon cancer	No increased risk	Increased risk

 

Clinical pearl: Always rule out IBD, colorectal cancer, and celiac disease before labeling a patient with IBS – especially in patients >50 or with alarming symptoms like weight loss, rectal bleeding or nocturnal symptoms.

Pathophysiology of IBS

IBS is multifactorial and still not fully understood. Key contributing factors include:

• Visceral hypersensitivity
• Altered gut motility
• Gut-brain axis dysfunction
• Post – infectious changes
• Microbiota alterations
• Psychological stressors ( anxiety / depression)

Role of Diet: FODMAPs Explained

Many patients with IBS report food -related triggers. The low FODMAP Diet is a central dietary intervention.

What are FODMAPs?

FODMAP= Fermentable Oligosaccharides, Disaccharides, Monosacchrides, and Polyols. These are short chain carbohydrates poorly absorbed in the gut and rapidly fermented by colonic bacteria, causing bloating, gas, and diarrhea.

High FODMAP foods:

• Oligosaccharides: Wheat, rye, onions, garlic
• Disaccharides: Milk, yogurt (lactose)
• Monosaccharide: Apples, Honey (excess fructose)
• Polyols: Sorbitol, mannitol (found in artificial sweeteners, some fruits)

Approach:

• Elimination phase: 4-6 weeks of low FODMAP intake
• Rechallenge phase: Gradual reintroduction to identify specific triggers
• Maintenance phase: Personalized, less restrictive diet

Evidence supports the low FODMAP diet in reducing global IBS symptoms, particularly bloating and abdominal pain.

Pharmacological Management

Tailored according to predominant symptoms:

IBS – C (Constipation – Predominant)

Drug/ Class	Mechanism	Notes
Fiber (e.g. psyllium)	Bulking agent	Soluble fiber preferred over insoluble
PEG (Polyethylene glycol)	Osmotic laxative	First- line for many patients
Lubiprostone	Chloride channel activator (CIC-2)	Increases intestinal fluid secretion
Linaclotide	Guanylate cyclase – C agonist	Enhances fluid secretion and motility
Prucalopride	5-HT4 receptor agonist	Promotility agent; used selectively

 

Pro tip: Avoid stimulant laxatives long-term duet to potential for tolerance and cathartic colon.

IBS – D (Diarrhea- Predominant)

Drug/ Class	Mechanism	Notes
Loperamide	µ-opioid receptor agonist	Symptomatic relief only; does not relieve pain
Alosetron	5-HT3 antagonist	Used in woman with severe IBS-D; rare ischemic colitis risk
Rifaximin	Non-absorbable antibiotic	Useful in IBS-D with bloating; 2-week course
Bile acid sequestrants	Binds bile acids (e.g. cholestyramine)	For patients with bile acid malabsorption
Eluxadoline	Mixed opioid receptor modulator	Avoid in patients without gallbladder or with pancreatitis risk

 

For pain and global symptoms

Drug/ Class	Role
Antispasmodics	Relieve abdominal cramps (e.g. dicyclomine, hyoscine)
Tricyclic Antidepressants (TCAs)	Modulate pain and motility (e.g. amitriptyline)
SSRIs/SNRIs	For patients with predominant anxiety or depression
Cognitive Behavioral Therapy (CBT)	Especially effective in refractory cases

 

Red Flag Symptoms (NOT typically of IBS)

Always investigate further if any of these are present:

• Age >50 with new onset symptoms
• Nocturnal diarrhea
• Unintentional weight loss
• Rectal bleeding
• Iron – deficiency anemia
• Family history of colorectal cancer or IBD

 

Summary Table: IBS subtypes and management

Subtype	Key Features	First – line Management
IBS-C	Pain + infrequent, hard stools	Fiber, PEG, linaclotide
IBS- D	Pain +frequent, loose stools	Loperamide, rifaximin
IBS- M	Mixed symptoms	Symptom – directed approach
IBS-U	Unclassified	Supportive, individualized

 

“The art of IBS management is not in curing, but in relieving symptoms, validating patient concerns, and enhancing quality of life.”