IBS: A Gastroenterologist's Guide to Diagnosis and Management

Irritable Bowel Syndrome (IBS) is one of the most common conditions I see in my gastroenterology clinics. It affects an estimated 10–15% of the UK population, yet many people suffer for years without a proper diagnosis or effective management plan. Here is my guide to understanding, diagnosing, and managing IBS.

What Is IBS?

IBS is a functional gastrointestinal disorder, meaning it affects how the gut works rather than causing visible structural damage. It involves a combination of abdominal pain, bloating, and altered bowel habits (diarrhoea, constipation, or both). While IBS is not dangerous, it can significantly affect your quality of life, work, and mental health.

The exact cause of IBS is not fully understood, but it involves a complex interaction between the gut and the brain — often called the gut-brain axis. Factors that contribute include altered gut motility, visceral hypersensitivity (the gut being overly sensitive to normal sensations), changes in the gut microbiome, and psychological stress.

Rome IV Diagnostic Criteria

IBS is diagnosed clinically using the Rome IV criteria. You are considered to have IBS if you have:

• Recurrent abdominal pain, on average, at least 1 day per week in the last 3 months
• Associated with two or more of the following: related to defecation, associated with a change in stool frequency, or associated with a change in stool form (appearance)
• Symptoms must have started at least 6 months ago

Importantly, your gastroenterologist will first rule out red flag symptoms such as unexplained weight loss, rectal bleeding, anaemia, or a family history of bowel cancer or inflammatory bowel disease.

IBS Subtypes

IBS is classified into subtypes based on the predominant bowel habit:

• IBS-D (Diarrhoea-predominant): Frequent loose or watery stools, often with urgency. More common in men.
• IBS-C (Constipation-predominant): Infrequent, hard stools with straining. More common in women.
• IBS-M (Mixed): Alternating between diarrhoea and constipation. The most frustrating subtype for many patients as symptoms are unpredictable.
• IBS-U (Unclassified): Symptoms don't clearly fit any of the above categories.

Identifying your subtype is important because treatment approaches differ significantly between them.

What Causes IBS?

IBS likely results from a combination of factors:

• Gut-brain axis dysfunction: Miscommunication between the brain and gut leads to altered motility and heightened pain perception.
• Gut microbiome changes: Research shows IBS patients often have different bacterial populations in their gut compared to healthy controls.
• Post-infectious IBS: Up to 10% of people develop IBS after a bout of gastroenteritis.
• Food sensitivities: Particularly to FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols).
• Stress and anxiety: While stress doesn't cause IBS, it significantly worsens symptoms through the gut-brain connection.

The Low FODMAP Diet

The low FODMAP diet is one of the most effective treatments for IBS, with approximately 70% of patients experiencing significant symptom improvement. FODMAPs are fermentable carbohydrates found in common foods that can trigger bloating, gas, and altered bowel habits in sensitive individuals.

The diet involves three phases:

• Elimination (4–6 weeks): Strict avoidance of high-FODMAP foods including wheat, onion, garlic, certain fruits, legumes, and dairy.
• Reintroduction (6–8 weeks): Systematic testing of each FODMAP group to identify your personal triggers.
• Personalisation: A long-term, less restrictive diet based on your individual tolerances.

My clinical nutrition training allows me to guide patients through this process safely, ensuring nutritional adequacy while identifying triggers.

Medication Options

Medications for IBS target specific symptoms:

• Antispasmodics (mebeverine, hyoscine, peppermint oil): Reduce abdominal cramps and pain.
• Loperamide: Controls diarrhoea in IBS-D.
• Linaclotide: Treats constipation in IBS-C by increasing fluid secretion in the bowel.
• Low-dose antidepressants (amitriptyline, SSRIs): Modify gut-brain signalling and reduce visceral pain — not prescribed for depression in this context.
• Rifaximin: An antibiotic sometimes used for bloating-predominant IBS.

When to See a Gastroenterologist

You should see a specialist if you experience any of the following:

• Symptoms that haven't improved with initial GP management
• Blood in your stool or unexplained weight loss
• Symptoms starting after age 50
• A family history of bowel cancer, ovarian cancer, or inflammatory bowel disease
• Night-time symptoms that wake you from sleep
• Persistent dyspepsia or acid reflux alongside IBS symptoms

I offer comprehensive IBS assessments at The Beaumont Hospital in Bolton and Spire Fylde Coast Hospital in Blackpool. Book an appointment — no GP referral needed.