Irritable bowel syndrome

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Reference: September 2025 | Issue 9 | Vol 11 | Page 24

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Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder characterised by chronic abdominal pain related to defecation, accompanied by alterations in stool frequency and form.

IBS is one of the most prevalent functional gastrointestinal disorders worldwide, with global prevalence estimates ranging from 9 per cent to 12 per cent, depending on the diagnostic criteria applied. Rates vary substantially according to geography, methodology, and the version of the Rome criteria used.

The condition is more common in women than men, with a female to male ratio of approximately 2:1 in many Western countries, although the gender difference is less pronounced in Asian populations. The disorder frequently presents in early adulthood, with the majority of cases diagnosed before the age of 50. IBS imposes a significant global health burden, leading to reduced quality of life, increased use of healthcare services, and economic costs from work absenteeism and reduced productivity.^1,2

Current understanding emphasises that IBS is a disorder of gut-brain axis dysfunction rather than stemming from identifiable structural pathology, reflecting the transition from earlier functional conceptions to a neuro-gastroenterological framework.¹

The mechanisms underlying IBS are complex and heterogeneous, including disturbances in gut-brain communication, heightened visceral sensitivity, abnormal gastrointestinal motility, dysbiosis of the intestinal microbiota, adverse responses to specific dietary components, and the influence of psychological and social factors.² Central to its development is dysregulation of the gut-brain axis, which disrupts bidirectional communication between the enteric and central nervous systems.

Patients frequently exhibit visceral hypersensitivity, resulting in exaggerated pain perception to normal physiological stimuli. Abnormalities in gastrointestinal motility, including accelerated or delayed transit times, further contribute to diarrhoea or constipation-predominant subtypes.

Increasing evidence implicates alterations in the intestinal microbiota, with reduced microbial diversity and dysbiosis linked to symptom generation. Low-grade mucosal immune activation and increased intestinal permeability have also been observed in subsets of patients.

Dietary intolerances, particularly to fermentable oligo- and di-monosaccharides, along with polyols (FODMAPs) and psychosocial stressors may exacerbate symptoms, highlighting the interplay between biological, microbial, and psychological factors in IBS pathophysiology.^{1, 2}

TABLE 1: The subtypes of irritable bowel syndrome (IBS)

Diagnosis

The diagnosis of IBS is primarily based on characteristic symptom patterns rather than identifiable structural or biochemical abnormalities. The Rome IV criteria, introduced in 2016, constitute the current gold standard for diagnosis. According to these criteria, patients must report recurrent abdominal pain occurring on average at least one day per week during the previous three months, with symptom onset at least six months before diagnosis. The pain must also be associated with two or more of the following:

• Relief with defecation
• Change in stool frequency
• Change in stool form.

IBS is further classified into subtypes based on the Bristol Stool Form Scale (BSFS):^{3, 4}

• IBS with constipation (IBS-C): Characterised by hard or lumpy stools more than 25 per cent of the time
• IBS with diarrhoea (IBS-D): Characterised by loose or watery stools more than 25 per cent of the time
• IBS with mixed bowel habits (IBS-M): Characterised by both hard/lumpy and loose/watery stools more than 25 per cent of the time
• IBS unclassified (IBS-U): Symptoms that do not meet the criteria for any of the above subtypes.

These criteria are designed to facilitate a positive diagnosis of IBS, distinguishing it from other gastrointestinal disorders that may present with similar symptoms.^3,4

Classification of IBS subtypes

Diagnosis is supported by a detailed history, physical examination, and selective laboratory testing, including full blood count, inflammatory markers, and coeliac serology. Endoscopic investigations are reserved for atypical presentations or alarm features, while abdominal x-ray may be considered in constipation-predominant cases.

Most patients can be diagnosed without invasive procedures. Clinicians should consider alternative conditions, such as inflammatory bowel disease, microscopic colitis, colorectal cancer, bile acid malabsorption, and dyssynergic defecation. In women with persistent bloating, CA-125 testing and pelvic ultrasound may be indicated to exclude ovarian malignancy. Assessment should also include dietary habits, medications, psychosocial stressors, and support systems.

Follow-up within two months is recommended to monitor symptom progression and exclude more serious pathology.^4,5,6

Treatment

There is no cure for IBS. Management focuses on symptom control and improving quality of life. Effective treatment generally combines education, lifestyle and dietary modifications, pharmacological therapy and, where indicated, psychological interventions. Establishing a strong clinician-patient relationship is central, with reassurance, validation of symptoms, involvement in decision-making, and clear discussion of realistic expectations. While a cure is unlikely, meaningful symptom relief and improved daily functioning are achievable.^7,8,9,10

Pharmacological therapy is guided by the predominant symptoms. Antispasmodics, including antimuscarinics such as dicycloverine, propantheline, hyoscine butylbromide, and otilonium bromide, reduce intestinal motility. Direct smooth muscle relaxants, such as alverine and mebeverine, relax intestinal muscles without antimuscarinic side effects. Peppermint oil also alleviates smooth muscle contraction, through calcium channel blockade, and can reduce IBS-related pain.

Butylscopolamine should be avoided in constipation-predominant IBS due to the risk of exacerbating constipation. For constipation, osmotic laxatives such as polyethylene glycol are commonly used, whereas stimulant laxatives may be considered if necessary. Lactulose is generally avoided because it increases gas and bloating. In patients with chronic constipation unresponsive to other therapies, linaclotide may be prescribed with caution due to potential fluid and electrolyte disturbances.

Loperamide is the first-line treatment for diarrhoea, slowing gut transit and reducing stool volume, although care is required in patients with mixed bowel habits.

Neuromodulators, including low-dose tricyclic antidepressants such as amitriptyline and, when indicated, selective serotonin reuptake inhibitors, may be used for persistent abdominal pain, with careful patient counselling regarding rationale and side effects. Psychological therapies, particularly cognitive behavioural therapy and gut-directed hypnotherapy, can benefit patients with persistent symptoms despite pharmacological management, although access may be limited.^7,8,9,10

Dietary and lifestyle modifications remain central to the effective management of IBS, forming the foundation for both first-line and adjunctive strategies aimed at symptom control. Patients are advised to establish regular eating patterns and avoid prolonged gaps between meals, which can contribute to dysregulated gastrointestinal motility and symptom flare-ups.

Adequate hydration, primarily through water intake, is essential for maintaining normal bowel function and preventing constipation, particularly in patients with IBS-C. Intake of caffeine, alcohol, carbonated beverages, and sorbitol should be minimised or avoided, especially in those with IBS-D, as these substances can exacerbate intestinal hypermotility and increase gas production, bloating, and urgency.^{1, 2, 8}

Physical activity is recommended as part of a holistic lifestyle approach, with moderate exercise shown to improve gut motility, reduce stress, and enhance overall wellbeing. Beyond its direct effects on the gut, physical activity also modulates the brain-gut axis by lowering stress reactivity, reducing anxiety, and enhancing mood, all of which are known to play a significant role in IBS symptom exacerbation. Exercise stimulates the release of endorphins and promotes autonomic balance, helping to reduce visceral hypersensitivity and abdominal discomfort.

Engaging in consistent activity also supports overall cardiovascular and metabolic health, which is particularly important as many patients with IBS report fatigue, sleep disturbances, and reduced quality of life. Moderate forms of exercise such as walking, cycling, swimming, or yoga are often most beneficial, as they combine physical movement with relaxation and stress-reducing effects. In contrast, high-intensity or strenuous exercise may worsen symptoms in some individuals, likely due to increased intestinal permeability and altered blood flow to the gut during exertion.

Dietary fibre plays an important role in IBS management, but not all types are helpful. Soluble fibre, such as psyllium (ispaghula husk), oats, apples, and citrus fruits, absorbs water in the gut and forms a soft gel. This can ease constipation by softening stools and can also help slow transit in diarrhoea, improving overall bowel regularity. Evidence suggests that psyllium in particular is effective in reducing abdominal pain and improving stool consistency.^1,2,7,8

In contrast, insoluble fibre, found in foods like wheat bran, nuts, and many raw vegetables, often worsens IBS symptoms. By increasing stool bulk and speeding gut transit, it can lead to bloating, cramping, and discomfort. Similarly, resistant starch in processed foods, legumes, and cooled starchy foods, is fermented in the colon, producing gas and contributing to bloating and flatulence.^1,2,7,8

For this reason, advice on fibre intake in IBS should be individualised, encouraging gradual introduction of soluble fibre with good hydration, while limiting insoluble and resistant forms to avoid symptom flare-ups.

For patients who continue to experience dietary-related symptoms despite general lifestyle adjustments, a low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet may be trialled as a second-line intervention.

This approach aims to reduce poorly absorbed short-chain carbohydrates that are fermented by colonic bacteria, potentially mitigating bloating, gas, and pain. However, such diets should ideally be undertaken under the guidance of a dietitian to ensure nutritional adequacy and appropriate reintroduction of foods.

In contrast, exclusion diets based on IgG antibody testing are not recommended, as current evidence does not support their efficacy in symptom management and may result in unnecessary dietary restrictions.^1,2,7,8

Together, these interventions emphasise the importance of personalised dietary and lifestyle strategies, considering individual symptom patterns, tolerances, and triggers, and forming a cornerstone of comprehensive IBS management.^1,2,8

Overall, successful IBS management requires an integrated approach that combines pharmacological, dietary, psychological, and supportive care tailored to individual patient needs.^1,2,8,10

Novel therapies

Increasingly, research is exploring the role of the gut microbiome and innovative treatments. Meta-analysis data have revealed potential symptomatic improvements following faecal microbiota transplantation in IBS, although high-quality clinical trials remain limited.

Recent investigative focus includes hormone-targeting strategies, such as modulation of insulin-like peptide 5 (INSL5) in IBS-D, which holds promise for more personalised treatment avenues.¹¹

Research is rapidly advancing, from short-chain fatty acids (SCFAs)-driven vagal signalling frameworks modelling the gut-brain axis at a molecular level, to dual-purpose diagnostic arrays capable of simultaneous IBS detection and low-FODMAP diet guidance. These may soon redefine the diagnostic and therapeutic landscapes.¹²

Ongoing research is expanding rapidly, exploring innovative therapies that span pharmacological agents, targeted dietary interventions, behavioural strategies, device-based approaches, and faecal microbiota transplantation.

These investigations not only aim to relieve the diverse symptoms of IBS, but also provide fresh insights into its underlying mechanisms. As this evidence base grows, it holds promise for more personalised and effective management strategies, ultimately improving patient quality of life and advancing our understanding of the syndrome.