Irritable Bowel Syndrome Through a Functional Lens

Irritable bowel syndrome is one of the most common reasons people seek help for digestive symptoms, and one of the most frustrating conditions for patients and practitioners alike. For patients, it can feel like a label given when nothing else is found. For practitioners, it can feel like a condition with no clear cause and no reliable treatment. Neither impression is accurate. Irritable bowel syndrome has well described mechanisms, a clear diagnostic approach and a range of treatments with good evidence. A functional lens adds a way of understanding why it developed in this person and what is keeping it going.

Making the diagnosis

The Rome IV criteria define irritable bowel syndrome as recurrent abdominal pain, on average at least one day a week in the last 3 months, associated with 2 or more of the following: related to defecation; associated with a change in stool frequency; associated with a change in stool form. Symptoms should have begun at least 6 months before diagnosis. It is subtyped by predominant stool pattern: constipation, diarrhoea, mixed or unclassified.

Using these criteria, surveys suggest that a few percent of adults worldwide meet the definition, with higher figures under older, broader criteria. It is more common in women and in younger adults.

Irritable bowel syndrome is a positive diagnosis based on symptoms, not simply a diagnosis of exclusion. But a limited set of tests is appropriate to exclude conditions that mimic it.

What to exclude

Bile acid diarrhoea deserves particular mention. Studies using specific testing have found it in a substantial minority of people diagnosed with diarrhoea predominant irritable bowel syndrome, and it responds to bile acid sequestrants.

The mechanisms

• Visceral hypersensitivity: normal amounts of gas or distension are perceived as painful.
• Altered motility: faster or slower transit, contributing to diarrhoea or constipation.
• Gut brain interaction: altered central processing of gut signals, influenced by stress, anxiety and past experiences.
• Post infection changes: after acute gastroenteritis, a proportion of people develop persistent symptoms, with low grade inflammation and altered barrier function.
• Microbiome differences: reported in many studies, although no consistent signature defines the condition.
• Food related triggers: fermentable carbohydrates and fat can provoke symptoms through distension and altered sensation, rather than through allergy.

Different mechanisms predominate in different people, which is why no single treatment works for everyone.

The functional lens: the story behind the symptoms

A timeline often reveals the onset and the drivers. Common patterns include symptoms beginning after gastroenteritis, during a period of intense stress, after a course of antibiotics, or with a change in routine such as shift work. Mediators that sustain symptoms frequently include irregular meals, eating quickly, high caffeine or alcohol intake, poor sleep, low activity, anxiety about symptoms and restrictive diets that have become increasingly narrow.

On the matrix, irritable bowel syndrome sits in assimilation but typically connects to communication through stress and sleep, and sometimes to defence and repair through post infection changes. This perspective helps build a plan that addresses the patient’s specific drivers.

A layered, evidence based plan

First layer: foundations

• A clear explanation of the diagnosis and its mechanisms, which in itself reduces anxiety and symptoms for many patients
• Regular meals, eating slowly, adequate fluid
• Reviewing caffeine, alcohol, spicy and fatty foods where these are triggers
• Soluble fibre such as psyllium, which gastroenterology guidelines recommend; insoluble fibre such as wheat bran may worsen symptoms
• Regular physical activity and sleep

Second layer: targeted dietary therapy

The low FODMAP diet has the best evidence of any dietary approach, delivered as a time limited elimination followed by structured reintroduction to identify personal triggers. It is ideally supported by a dietitian. It is not appropriate for people with eating disorders or significant weight loss.

Third layer: symptom specific options

• Peppermint oil has evidence for global symptoms and pain.
• Antispasmodics for cramping pain.
• Laxatives for constipation, and specific prescription treatments for constipation predominant disease.
• Antidiarrhoeals as needed for diarrhoea, and specific treatments where appropriate, including bile acid sequestrants if bile acid diarrhoea is identified.
• Rifaximin has evidence in diarrhoea predominant disease in some settings.

Fourth layer: gut brain therapies

• Gut directed hypnotherapy and cognitive behavioural therapy, both with good evidence.
• Low dose tricyclic antidepressants or other neuromodulators for pain, prescribed by a doctor.

Probiotics

Evidence is mixed and strain specific. Some patients benefit; guideline recommendations vary, and a time limited trial of a specific product with clear review is a reasonable option for patients who wish to try one.

Common pitfalls

• Endless testing. Once appropriate exclusions are done, repeated investigations reinforce the idea that something serious is being missed.
• Ever narrowing diets. Patients who eliminate food after food without reintroduction risk nutritional inadequacy and fear of eating.
• Ignoring the brain. Psychological therapies are among the most effective treatments and are underused.
• Missing bile acid diarrhoea or microscopic colitis. Both are treatable and often overlooked.
• Attributing new symptoms in later life to long standing irritable bowel syndrome without reassessment.

An illustrative case

A 31 year old nurse has had diarrhoea predominant irritable bowel syndrome for 3 years, beginning after a severe bout of food poisoning. She works rotating shifts, drinks 4 coffees a day, eats irregularly and has become anxious about eating at work. She has removed gluten, dairy and onion without lasting benefit.

Coeliac serology, calprotectin and blood tests are normal. Her plan begins with regular meals around her shifts, reduced caffeine and psyllium. A dietitian supervises a low FODMAP trial and reintroduction, which identifies large amounts of fructans and lactose as triggers while she tolerates gluten containing foods in usual portions. Because her diarrhoea persists, her doctor arranges testing for bile acid diarrhoea, which is positive, and a bile acid sequestrant helps considerably. She also begins a gut directed hypnotherapy programme. At 6 months her symptoms are much improved and her diet is broader than before. Several mechanisms were involved, and each was addressed.

A treatable condition

Irritable bowel syndrome is not a dead end diagnosis. It is a recognisable disorder of gut brain interaction with identifiable drivers and effective treatments. A careful diagnosis, a functional understanding of the patient’s story and a layered plan offer most patients meaningful relief.