Irritable bowel syndrome: a contemporary view of pathogenesis and treatment

Irritable bowel syndrome (IBS) is one of the most common chronic gastrointestinal disorders, substantially affecting patients’ quality of life and ability to work. The contemporary concept views IBS not simply as a functional disorder of intestinal motility, but as a disorder of gut–brain interaction (DGBI) involving motor, sensory, immune, microbiota-related, and psychophysiological mechanisms.

What is irritable bowel syndrome?

According to the current Rome IV concept, IBS is characterized by a combination of recurrent abdominal pain associated with defecation and/or changes in stool frequency and form, in the absence of a structural disease capable of explaining the symptoms.

This approach differs fundamentally from the previous view of IBS as a condition in which “nothing is found.” Studies demonstrate objective alterations in intestinal motility, visceral sensitivity, the intestinal barrier, immune regulation, and the microbiome.

How common is IBS?

According to the review by Staudacher et al., IBS is present in approximately 5–10% of the global population at any given time and is more common in women.

What forms of IBS are there?

Clinical classification is based primarily on stool characteristics:

• IBS with predominant constipation (IBS-C) — constipation and difficult defecation predominate;
• IBS with predominant diarrhea (IBS-D) — loose or mushy stools predominate;
• mixed type (IBS-M) — alternating constipation and diarrhea;
• unclassified type (IBS-U) — symptoms do not meet the criteria for the three main subtypes.

The same patient may change disease phenotype over time.

Clinicians should also consider overlap disorders. IBS frequently coexists with functional dyspepsia and other functional gastrointestinal disorders.

Why does IBS develop?

There is no single cause of the disease. The current model proposes an interaction of multiple factors:

genetic predisposition → microbiome changes → impairment of the intestinal barrier and immune regulation → altered motility and visceral sensitivity → disruption of bidirectional communication between the gut and the brain.

Potential triggers include intestinal infections, dietary factors, stress, sleep disturbances, psycho-emotional factors, and other environmental exposures.

Post-infectious IBS is of particular importance. After an intestinal infection, some patients may have persistent disturbances of the microbiota, intestinal barrier, and intestinal sensitivity.

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How do symptoms develop? — the role of the gut–brain axis

The gut–brain axis occupies a central place in the contemporary understanding of IBS and represents a bidirectional neurohumoral communication system between the central nervous system and the gastrointestinal tract.

The main pathophysiological mechanisms include:

• visceral hypersensitivity;
• impaired motility and intestinal transit;
• alterations in the intestinal microbiota;
• impairment of the intestinal barrier;
• changes in immune and neuroendocrine regulation;
• effects of stress and dysregulation of the hypothalamic-pituitary-adrenal axis (HPA axis).

Stress can activate the HPA axis and autonomic nervous system, altering intestinal motility, immune responses, and perception of visceral stimuli.

What role does the microbiome play?

The microbiome is considered one of the key components of pathogenesis. Patients with IBS show changes in the composition and diversity of the intestinal microbiota. Reductions in some Lactobacilli and Bifidobacteria and increases in several Enterobacteria, Escherichia coli, Ruminococcus gnavus, and Bacteroides have been described.

However, these changes cannot yet be interpreted as a single specific “IBS microbiome.”

What role does diet play?

Dietary therapy is currently considered one of the first-line components of IBS treatment. The approach should be individualized: the goal is not to eliminate as many foods as possible, but to identify a diet that reduces symptoms without unnecessarily restricting dietary diversity.

Low-FODMAP diet

The low-FODMAP diet is the most extensively studied specialized dietary intervention for IBS.

FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols. These include fructans, galacto-oligosaccharides, lactose, excess fructose, and polyols such as sorbitol and mannitol.

These carbohydrates are poorly or incompletely absorbed in the small intestine. They increase the osmotic load and undergo fermentation by intestinal bacteria, which may lead to increased gas production, bloating, pain, and changes in stool characteristics.

An important advantage of low-FODMAP is its ability to reduce abdominal pain, bloating, and dissatisfaction with stool consistency; in a network meta-analysis, this approach ranked highest among the diets compared.

However, low-FODMAP should not become a permanently strict elimination diet. Three stages are recommended: short-term FODMAP restriction, sequential food reintroduction, and subsequent personalization of the diet.

This is important both for preserving dietary diversity and for minimizing undesirable microbiome changes, because the strict phase may reduce some beneficial bacteria, particularly bifidobacteria.

Mediterranean diet: how is it different?

The Mediterranean diet differs fundamentally from low-FODMAP. It does not directly target restriction of fermentable carbohydrates but represents an overall healthy dietary pattern rich in vegetables, fruits, legumes, whole grains, nuts, seeds, and olive oil, with relatively little red meat.

The potential benefit of this approach in IBS is not limited to gastrointestinal symptoms. A Mediterranean diet may have favorable effects on the microbiome and psycho-emotional state, which is particularly important for patients with both IBS and anxiety-depressive symptoms.

However, the evidence base specifically for IBS remains considerably weaker than for low-FODMAP. To date, only one non-randomized study has directly compared Mediterranean and low-FODMAP diets in IBS.

For mild gastrointestinal symptoms, the Mediterranean diet may be an attractive baseline strategy, particularly if the patient is interested in simultaneously addressing psycho-emotional factors. More pronounced symptoms may require individualized dietary modification.

Psychobiotics: can the gut–brain axis be influenced through the microbiome?

Psychobiotics are substances or products capable of influencing the microbiome–gut–brain axis. This category includes probiotics, prebiotics, synbiotics, postbiotics, and fermented foods.

The theoretical basis of this approach is that intestinal microorganisms may influence neurotransmitter systems, immune responses, metabolites, and the hypothalamic-pituitary-adrenal axis. Therefore, microbiome modification could potentially affect gastrointestinal and psycho-emotional symptoms simultaneously.

In the context of IBS, psychobiotics are of interest as a therapeutic direction directly linked to gut–brain axis mechanisms.

How should a diet be selected for an individual patient?

These approaches have different therapeutic objectives:

At the same time, unjustifiably strict restrictions should be avoided. Some patients with IBS may develop fear of specific foods and avoidant eating behavior, further impairing quality of life.

How are IBS and psycho-emotional factors related?

Psychological factors should not be regarded as evidence that IBS is a “psychosomatic” disease. Current data indicate a bidirectional interaction between gastrointestinal and psychological symptoms.

Stress, anxiety, and mood disturbances may increase the severity of gastrointestinal symptoms through gut–brain axis mechanisms. Therefore, the patient’s psycho-emotional state should be assessed alongside gastroenterological symptoms.

What is brain–gut behaviour therapy?

Brain–gut behaviour therapy (BGBT) is not intended to treat IBS as a “psychological disease,” but rather to modify cognitive and behavioral mechanisms that may amplify symptom perception.

For example, a patient may develop marked anxiety about being unable to reach a toilet quickly, fear of certain foods, or catastrophizing of pain. This leads to avoidance, activity restriction, and heightened attention to intestinal sensations, which in turn may perpetuate symptoms.

BGBT includes:

• cognitive behavioural therapy (CBT);
• gut-directed hypnotherapy;
• psychodynamic therapy;
• various relaxation techniques.

A meta-analysis of randomized studies involving 4072 patients showed that CBT and gut-directed hypnotherapy are among the most effective behavioral methods in the long term.

Can mindfulness-based stress reduction help?

Mindfulness-based stress reduction (MBSR) is another approach targeting mechanisms of gut–brain interaction.

Mindfulness involves intentionally directing attention to the present moment without judging one’s sensations. This allows patients to observe symptoms without automatically progressing to an anxious response and catastrophizing.

A typical MBSR program may include approximately 45 minutes of daily practice for 8 weeks. Evidence in IBS is currently less convincing than for CBT and gut-directed hypnotherapy, although available findings indicate a potential reduction in symptoms and improvement in patients’ ability to cope with them.

How can digital tools be used in treatment?

Digital tools — mobile applications, websites, and digital programs — may expand patients’ access to dietary and behavioral interventions.

Digital therapy should not replace clinical assessment. Applications may be used for patient education and monitoring of symptoms, physical activity, diet, sleep, and mindfulness practices.

Digital tools are particularly promising for delivering self-management and behavioral therapy programs in patients with mild or moderate IBS. If the effect is insufficient, individualized assessment and transition to face-to-face care are necessary.

Additional facts on related topics are available via LINK 

How is IBS treated?

The contemporary treatment strategy is multimodal and personalized. It includes patient education, lifestyle modification, dietary therapy, symptom-oriented pharmacotherapy, and, when necessary, brain–gut behaviour therapy.

In IBS-D, loperamide may be used to control diarrhea, and if the effect is insufficient, agents targeting intestinal motility, secretion, and sensitivity, including rifaximin, eluxadoline, and alosetron, may be used in appropriate clinical situations.

In IBS-C, osmotic laxatives are used, and if the effect is insufficient, secretagogues including linaclotide and plecanatide may be prescribed.

For constipation, soluble fiber, particularly psyllium, plays an important role. Unlike coarse insoluble fiber, which may worsen bloating in some patients, psyllium can improve stool consistency and relieve constipation symptoms.

Antispasmodics and other symptom-oriented agents are used to control abdominal pain; for persistent pain, neuromodulators, primarily tricyclic antidepressants, may be used.

Thus, treatment should correspond to the IBS phenotype: in IBS-C, correction of constipation becomes the priority; in IBS-D, diarrhea control is prioritized; and with pronounced pain, bloating, or coexisting psycho-emotional symptoms, a broader therapeutic strategy is required.

Key conclusions for clinical practice

The contemporary model of IBS extends far beyond isolated treatment of intestinal motility disorders. The gut–brain axistakes a central role, and treatment becomes personalized.

Regarding nutrition, the strongest evidence currently supports the low-FODMAP diet, which should be used for a limited period followed by food reintroduction. The Mediterranean diet is of interest as a broader and more sustainable healthy dietary pattern, particularly in patients with mild symptoms. Psychobiotics are a promising direction related to modulation of interactions among the microbiome, gut, and brain.

With persistent symptoms, brain–gut behaviour therapy, particularly cognitive behavioural therapy and gut-directed hypnotherapy, plays an important role. Mindfulness-based stress reduction may be used as an additional method for managing stress burden and symptoms. Digital tools may expand access to dietary, educational, and behavioral support but should be used as an adjunct to clinical care.

Thus, the optimal IBS treatment strategy is not the search for a single “ideal” diet or medication, but a combination of individualized dietary therapy, management of predominant gastrointestinal symptoms, and interventions targeting gut–brain axis mechanisms through behavioral and other non-pharmacological methods.

References

1. Huang K-Y, Wang F-Y, Lv M, Ma X-X, Tang X-D, Lv L. Irritable bowel syndrome: Epidemiology, overlap disorders, pathophysiology and treatment. World Journal of Gastroenterology. 2023;29(26):4120–4135.doi:10.3748/wjg.v29.i26.4120.
2. Staudacher HM, Black CJ, Teasdale SB, Mikocka-Walus A, Keefer L. Irritable bowel syndrome and mental health comorbidity — approach to multidisciplinary management. Nature Reviews Gastroenterology & Hepatology. 2023. doi:10.1038/s41575-023-00794-z.