Table of contents
Irritable bowel syndrome (IBS) can significantly impact daily quality of life, social relationships, and work performance. Despite its prevalence—affecting at least 10–15% of the population—diagnosing and treating IBS remains a challenge. This is due to the complex development and progression of the condition, which requires a multidisciplinary approach to understand and manage effectively. Disruptions in the gut-brain axis, alterations in the gut microbiome, current or past gastrointestinal infections, food intolerances or allergies, and genetic factors must all be considered. [1]
What is IBS?
IBS is a chronic, functional disorder of the gastrointestinal tract. It is characterized by a variety of symptoms that may appear and disappear periodically and are associated with changes in bowel movements (motility), depending on the IBS subtype. Although the condition does not cause significant tissue damage, it can be a lifelong problem. [2–4]
Symptoms of IBS
The symptoms of IBS vary but commonly include:
- Abdominal cramps
- Bloating
- Pain
- Discomfort
- Diarrhoea or constipation, or alternating between the two. [2–4]
Figure 1. Symptoms of IBS
Less typical symptoms may include fatigue, nausea, back pain, urinary issues, or mucousy stools. [2]
Symptoms often worsen after eating certain foods, particularly those containing fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs), such as lactose or gluten. Common triggers include slow-absorbing carbohydrates (e.g., dairy products, beans, lentils, apples, flour), foods high in biogenic amines (e.g., wine, beer, salami, cheese), histamine-releasing foods (e.g., milk, wine, beer, pork), and fried or fatty foods. [5]
IBS symptoms can be hard to distinguish from other conditions that often coexist with the disorder, including:
- Chronic pain syndromes such as fibromyalgia or pelvic pain
- Chronic fatigue syndrome
- Digestive disorders like SIBO, dyspepsia, or reflux
- Psychological conditions such as anxiety or depression. [6]
These may act as risk factors for IBS, alongside certain sociodemographic characteristics such as female gender (women are about twice as likely to be diagnosed) and age (typically young to middle adulthood). [3]
Types of IBS
IBS is classified based on bowel movement patterns and stool consistency. Many individuals experience normal bowel movements on some days and abnormal ones on others. Different treatments are tailored to each IBS subtype, making it important to distinguish among them.
Figure 2. IBS subtypes based on stool consistency and bowel habits
An undefined IBS type also exists, in which symptoms and bowel movement patterns don’t clearly fit into a specific subtype, but a diagnosis can still be made. [3], [5], [7]
Diagnosis of IBS
Currently, there is no specific lab or imaging test for IBS. Diagnosis is symptom-based, using widely accepted criteria. IBS can be diagnosed if a person has experienced recurrent abdominal pain at least once per week over the past three months, along with at least two of the following: pain related to defecation, changes in stool frequency, or changes in stool consistency. Symptoms must have started at least six months prior. [8]
The diagnostic process often includes tests to rule out more severe pathologies or those with similar symptoms [6], [9]. These may include colonoscopy, endoscopy, CT scans, lactose intolerance testing, SIBO breath tests, and various stool or microbiome analyses. [4]
Red flags warranting further investigation include persistent pain unrelieved by defecation, nighttime pain, fever, weight loss, poor appetite, vomiting, or iron-deficiency anaemia. These symptoms could indicate inflammatory bowel diseases (ulcerative colitis or Crohn’s disease) or even colon cancer. [5], [10]
Professional guidelines suggest minimizing unnecessary testing, as it can be an unnecessary burden for patients and the healthcare system [5], [11]. However, relying solely on symptom-based diagnosis can risk overlooking other conditions [12–13]. Ultimately, test selection depends on physician judgment and resource availability. [14]
Development of IBS
The pathogenesis and pathophysiology of IBS are not yet fully understood. It is a multifactorial process involving several contributing factors, such as impaired communication along the gut-brain axis, immune dysfunction, alterations in gut flora, food intolerances, and genetic predisposition. It remains unclear which of these factors trigger the onset of IBS and which exacerbate its symptoms in certain individuals. [15]
The role of the gut-brain axis in the development of IBS
One of the most widely accepted explanations for IBS is dysfunction in the gut-brain axis [1]. All four layers of the intestinal wall are densely supplied with blood vessels and nerves and contain approximately 100 million nerve cells, forming the enteric nervous system. This system is in constant two-way communication with the central nervous system (the brain and spinal cord), meaning that central nervous system overload (e.g., stress, anxiety, or sleep deprivation) can manifest as painful muscular contractions in the intestinal wall. These altered contractions affect intestinal motility, leading to either diarrhoea or constipation. If the contractions affect a small segment of the intestine, the contents become stuck and dry, causing constipation. If a longer segment is involved, contents pass too quickly, preventing water reabsorption and resulting in diarrhoea. [16]
Gut-brain axis dysfunction also contributes to visceral hypersensitivity, a hallmark of IBS. This condition causes the intestinal tract to respond with exaggerated pain to normal stimuli (such as gas or bloating), meaning the pain threshold is abnormally low for colonic distension. [3], [15]
These issues are closely linked to stress responses and psychological symptoms. According to a 2021 meta-analysis, depression and severe anxiety occur 40% more frequently in individuals with IBS [17]. The hypothalamic-pituitary-adrenal (HPA) axis, involved in stress response, may become hyperactive and secrete certain hormones abnormally (e.g. coretisol), altering gut motility, increasing visceral sensitivity, triggering immune responses, and disturbing gut flora. This process can also work in reverse: stress and anxiety may be consequences of gut dysfunction, such as low-grade inflammation, increased intestinal permeability, or imbalances in the microbiome. [15], [18]
Figure 3. Central nervous system overload (e.g., stress, anxiety, or sleep deprivation) causes painful muscular contractions in the intestinal wall
The role of the gut microbiome in the development of IBS
The gut microbiome is a complex ecosystem made up of bacteria, archaea, fungi, and viruses. It influences brain function by directly or indirectly interacting with the enteric nervous system and, through it, the gut-brain axis. [1]
The gut microbiome in people with IBS differs from that of healthy individuals, though findings vary between studies. These inconsistencies may stem from the variability between IBS subtypes and individual differences, as well as the relative novelty of this field. However, common findings include reduced microbial diversity, overgrowth of Proteobacteria, Veillonella, and certain Firmicutes, and a reduction in Bacteroidetes, Bifidobacteria, Lactobacilli, and methane-producing bacteria. [15], [19–20]
Dysbiosis—an imbalance in the gut microbial community—can lead to increased intestinal permeability. This may result from bacterial toxins, inflammatory mediators, or reduced production of short-chain fatty acids. In this so-called “leaky gut,” pathogens, toxins, or undigested food particles can penetrate the thin, fibrous connective tissue layer beneath the intestinal epithelial cells and enter the bloodstream. Their antigens trigger pro-inflammatory cytokines (e.g., IL-6, IL-8, TNF-α) via immune cells in the enteric nervous system, leading to low-grade inflammation that affects neurons in both the gut and the brain. This inflammation raises cortisol levels, potentially causing anxiety and concentration issues [1]. These psychological symptoms can then worsen IBS symptoms via the stressed gut-brain axis.
Figure 4. Dysbiosis refers to a disruption in the optimal balance and composition of the microbial community, during which the permeability of the intestinal mucosa increases.
Dysbiosis can also lead to small intestinal bacterial overgrowth (SIBO) under certain conditions [21]. One study found that 75% of IBS patients (157 of 202) tested positive for lactulose hydrogen breath tests, indicating SIBO [22]. Given the high prevalence, SIBO may be worth investigating as a more specific, treatable condition.
Approximately 10% of IBS cases are triggered by acute infectious gastroenteritis [23]. Individuals with genetic variants related to innate immunity and mucosal barrier function—as well as those with high stress or anxiety—are at increased risk of developing post-infectious IBS. This form typically presents as diarrhoeal IBS. Substances released during the infection also increase intestinal permeability. [24]
The role of food allergies and sensitivities in the development of IBS
Diet plays a key role in IBS pathogenesis by influencing the gut microenvironment, reducing colonic fermentation, and modulating immune activation, which can induce low-grade inflammation [25]. The role of food allergy and intolerance in IBS, however, is not fully understood. While true food allergies are rarely responsible, many patients report symptom exacerbation after consuming certain foods or drinks [26]. For instance, even with a negative celiac disease test, some individuals experience IBS symptoms after consuming gluten—suggesting an overlap with non-celiac gluten sensitivity [27]. Many IBS sufferers are sensitive to FODMAPs, and inadequate digestion of gluten and proteins like casein (from milk) can increase inflammation and stimulate the innate immune system. IgE and IgG receptors on mast cells can respond to these foods by releasing histamine and other inflammatory mediators, affecting various systems including the skin, nervous system, cardiovascular and respiratory tracts, and gastrointestinal system. These immune responses may lead to IBS symptoms, especially abdominal pain triggered by food sensitivities or allergies. [28]
Genetic predisposition to IBS
IBS is more common in families with multiple affected members, suggesting a genetic component, although environmental factors play a predominant role [29]. The genetic risk can range from complex polygenic inheritance—where various common genetic variants interact—to cases involving a single rare gene mutation. For example, mutations in the SC5NA gene, which encodes sodium ion channels, have been associated with abdominal pain in IBS. Additionally, polymorphisms in genes involved in serotonin signalling, immune regulation, and mucosal barrier function have also been linked to IBS pathogenesis. [15]
The role of microbial neurotransmitters and metabolites in the development of IBS
Although IBS is not classified as a typical inflammatory bowel disease, several studies have shown low-grade inflammation in the digestive tract, marked by increased numbers of enterochromaffin cells, intraepithelial lymphocytes, and mast cells [30]. Neurotransmitters produced by these cells—as well as by gut microbiota—play a significant role in IBS symptom development [1], [31]. Additionally, microbial metabolites influence essential gut functions, and an altered metabolic profile of gut bacteria may contribute to IBS symptoms [1], [32]. The neurotransmitters and metabolites listed below are of paramount importance in the development and progression of IBS:
Figure 5. Certain microbial metabolites influence key physiological processes in the gut, meaning that an altered metabolic profile of gut bacteria may also contribute to the symptoms of IBS.
Treatments of IBS
Challenges in the management of IBS
Managing IBS can be complex, but symptom relief is achievable. Many people with IBS consult multiple healthcare providers without success. Practitioners often struggle to diagnose and identify the root cause, while patients frequently feel dissatisfied with their care. Treatment outcomes depend greatly on the attitudes of both professionals and patients, the severity of comorbidities and symptoms, and persistent misconceptions surrounding the condition. [47]
For physicians, IBS can be a source of frustration—partly due to the absence of standardized treatment protocols. Some doctors may also believe that the condition is driven more by the patient’s psychological state than by clinical treatment, which can lead to disconnects in the doctor-patient relationship when patients don’t share this view. [48]
Ideally, a multidisciplinary team—comprising, for example, an internist, nutritionist, and psychologist or psychiatrist—can offer long-term, collaborative support. For successful management, the patient must take an active role, as lifestyle changes are a critical part of the process. [49–50]
Figure 6. Treatments of IBS
Medication for IBS
IBS symptoms can be managed with conventional medical treatments. Depending on the subtype of IBS, different medications may be prescribed. Laxatives are primarily used for constipation-predominant IBS, while antidiarrheals are used for diarrhoea-predominant IBS. [4]
Antispasmodics can relieve pain and cramps in some IBS patients [51]. These fall into two categories: 1. Neurotropic antispasmodics, which act on the nervous system to inhibit smooth muscle contractions (e.g., hyoscine butylbromide). 2. Musculotropic antispasmodics, which act directly on muscle tissue to reduce spasms (e.g., mebeverine), and may also help in constipation-predominant IBS. [6], [52]
Research on antidepressants in IBS has yielded mixed results [53]. Tricyclic antidepressants appear to be especially effective for diarrhoea-predominant IBS, while selective serotonin reuptake inhibitors may help more with constipation-predominant IBS. Serotonin-norepinephrine reuptake inhibitors are less commonly used however, they have shown promising results [52], [54]. These medications can relieve IBS symptoms even in patients without depression, and often at lower doses than typically used for mood disorders. [53]
Antibiotics are gaining attention in IBS treatment, especially given the emerging role of the gut microbiota. In some cases, particularly where SIBO is also present (mainly in diarrhoeal IBS), antibiotics may help by reducing the population of harmful gut bacteria. Treatment is usually short-term but may require repetition, and should always be medically supervised [55–56]. While antibiotics can reduce abnormal bacterial overgrowth, they may also deplete beneficial bacteria, potentially leading to other issues detectable through stool microbiome testing.
Chronic use of proton pump inhibitors (PPIs) to reduce stomach acid can also disrupt the microbiome, lowering bacterial diversity and promoting pathogenic overgrowth. PPI use has been linked to SIBO, which may contribute to IBS symptoms. [57]
The treatment of IBS with diet and nutritional supplements
Nutritional factors play a crucial role in managing IBS. For example, fibre intake can both alleviate and worsen symptoms. Short-chain, soluble, and highly fermentable fibres (such as oligosaccharides) can lead to rapid gas production, causing bloating and abdominal discomfort. In contrast, long-chain, viscous, soluble fibres with moderate fermentability—like psyllium—tend to produce less gas and may improve overall symptoms and relieve constipation. [58]
The low-FODMAP diet is one of the most commonly used dietary approaches for IBS. It involves reducing fermentable carbohydrates that are poorly absorbed in the small intestine and lead to gas formation. This diet has been shown to reduce symptoms by easing pressure on the gut wall, which is especially important for individuals with visceral hypersensitivity. However, long-term adherence can be difficult and may negatively impact gut microbiota diversity. [59–60]
Many IBS patients (due to suspected or confirmed food intolerances) follow other elimination diets that exclude common allergens [5], [61]. While such diets may offer short-term symptom relief, prolonged dietary restrictions are not always advisable, as they can further reduce microbiome diversity. Professional guidance is recommended to maintain nutritional balance. [5]
Simple practices like eating meals at regular times can help regulate bowel function [1], [13]. The effects of meal skipping or intermittent fasting vary by IBS type and individual physiology. These practices may be beneficial for some, but could worsen symptoms for others, so professional consultation is advised before adopting them. [62]
Many individuals with IBS also turn to herbal remedies. For example, aloe vera is often used for constipation-predominant IBS, although more scientific research is needed to confirm its effectiveness. Peppermint oil, on the other hand, has been shown to relieve abdominal pain and bloating, particularly in diarrhoea-predominant IBS [13], [63]. Enteric-coated peppermint oil capsules slowly release the active ingredient in the small intestine, helping to reduce bloating and pain during defecation [1]. Vitamin D and vitamin B6 supplementation can also support symptom management, given their roles in gut health and inflammation control, as previously discussed. [1]
A promising and evolving area is the use of probiotics in IBS treatment. Probiotics are beneficial bacteria found in certain foods and supplements that help restore gut microbiome balance. They may: normalize inflammatory cytokine levels, improve gut motility, reduce intestinal permeability, inhibit the overgrowth of fermentative bacteria in the small intestine [64]. Specific strains of probiotics have been shown to alleviate different symptoms. For example: Bifidobacterium breve, B. longum, and Lactobacillus acidophilus may reduce abdominal pain. Lactobacillus plantarum may relieve bloating. [56], [65]
While probiotics hold promise, their effectiveness varies between individuals. More research is needed to identify optimal strains and dosages. Fecal genome testing offers a personalized approach by providing a detailed view of an individual’s gut microbiome, allowing for tailored probiotic therapy.
IBS and psychological well-being
Given IBS’s multifactorial nature and its close links with the gut-brain axis and HPA axis, psychological factors are gaining increasing attention in IBS management.
As part of lifestyle changes, stress reduction is key. Relaxation techniques (such as autogenic training), meditation, regular physical activity, and exercise can all help decrease the frequency and severity of IBS symptoms. Exercise also improves mood and supports intestinal motility. Activities like cycling have been shown to reduce bloating and gas, while yoga has been found to ease symptoms by influencing the parasympathetic and sympathetic nervous systems. [13]
Psychological therapies, including psychoeducation, cognitive behavioural therapy, and gut-directed hypnotherapy, may offer further benefits. Although current evidence isn’t yet strong enough to recommend these approaches as standalone first-line treatments, clinical guidelines suggest them for patients who do not respond adequately to medication. [66]
In summary, while more research is needed to confirm the effectiveness of psychotherapeutic and alternative approaches, existing evidence indicates that addressing psychological factors and managing stress can play a significant role in relieving IBS symptoms and improving quality of life.
References
[1] ‘Biovis_Reizdarmsyndrom_EN.pdf’ https://www.biovis.eu/wp-content/uploads/Biovis_Reizdarmsyndrom_EN.pdf
[2] ‘Irritable bowel syndrome (IBS)’, nhs.uk, Oct. 24, 2017 https://www.nhs.uk/conditions/irritable-bowel-syndrome-ibs/
[3] ‘What Is Irritable Bowel Syndrome (IBS)?’, Cleveland Clinic https://my.clevelandclinic.org/health/diseases/4342-irritable-bowel-syndrome-ibs
[4] ‘Irritable bowel syndrome – Symptoms and causes’, Mayo Clinic https://www.mayoclinic.org/diseases-conditions/irritable-bowel-syndrome/symptoms-causes/syc-20360016
[5] P. Moayyedi et al., ‘Irritable bowel syndrome diagnosis and management: A simplified algorithm for clinical practice’, United Eur. Gastroenterol. J., vol. 5, no. 6, pp. 773–788, Oct. 2017, DOI: https://doi.org/10.1177/2050640617731968
↓ Read More ↓Table of contents
Irritable bowel syndrome (IBS) can significantly impact daily quality of life, social relationships, and work performance. Despite its prevalence—affecting at least 10–15% of the population—diagnosing and treating IBS remains a challenge. This is due to the complex development and progression of the condition, which requires a multidisciplinary approach to understand and manage effectively. Disruptions in the gut-brain axis, alterations in the gut microbiome, current or past gastrointestinal infections, food intolerances or allergies, and genetic factors must all be considered. [1]
What is IBS?
IBS is a chronic, functional disorder of the gastrointestinal tract. It is characterized by a variety of symptoms that may appear and disappear periodically and are associated with changes in bowel movements (motility), depending on the IBS subtype. Although the condition does not cause significant tissue damage, it can be a lifelong problem. [2–4]
Symptoms of IBS
The symptoms of IBS vary but commonly include:
- Abdominal cramps
- Bloating
- Pain
- Discomfort
- Diarrhoea or constipation, or alternating between the two. [2–4]
Figure 1. Symptoms of IBS
Less typical symptoms may include fatigue, nausea, back pain, urinary issues, or mucousy stools. [2]
Symptoms often worsen after eating certain foods, particularly those containing fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs), such as lactose or gluten. Common triggers include slow-absorbing carbohydrates (e.g., dairy products, beans, lentils, apples, flour), foods high in biogenic amines (e.g., wine, beer, salami, cheese), histamine-releasing foods (e.g., milk, wine, beer, pork), and fried or fatty foods. [5]
IBS symptoms can be hard to distinguish from other conditions that often coexist with the disorder, including:
- Chronic pain syndromes such as fibromyalgia or pelvic pain
- Chronic fatigue syndrome
- Digestive disorders like SIBO, dyspepsia, or reflux
- Psychological conditions such as anxiety or depression. [6]
These may act as risk factors for IBS, alongside certain sociodemographic characteristics such as female gender (women are about twice as likely to be diagnosed) and age (typically young to middle adulthood). [3]
Types of IBS
IBS is classified based on bowel movement patterns and stool consistency. Many individuals experience normal bowel movements on some days and abnormal ones on others. Different treatments are tailored to each IBS subtype, making it important to distinguish among them.
Figure 2. IBS subtypes based on stool consistency and bowel habits
An undefined IBS type also exists, in which symptoms and bowel movement patterns don’t clearly fit into a specific subtype, but a diagnosis can still be made. [3], [5], [7]
Diagnosis of IBS
Currently, there is no specific lab or imaging test for IBS. Diagnosis is symptom-based, using widely accepted criteria. IBS can be diagnosed if a person has experienced recurrent abdominal pain at least once per week over the past three months, along with at least two of the following: pain related to defecation, changes in stool frequency, or changes in stool consistency. Symptoms must have started at least six months prior. [8]
The diagnostic process often includes tests to rule out more severe pathologies or those with similar symptoms [6], [9]. These may include colonoscopy, endoscopy, CT scans, lactose intolerance testing, SIBO breath tests, and various stool or microbiome analyses. [4]
Red flags warranting further investigation include persistent pain unrelieved by defecation, nighttime pain, fever, weight loss, poor appetite, vomiting, or iron-deficiency anaemia. These symptoms could indicate inflammatory bowel diseases (ulcerative colitis or Crohn’s disease) or even colon cancer. [5], [10]
Professional guidelines suggest minimizing unnecessary testing, as it can be an unnecessary burden for patients and the healthcare system [5], [11]. However, relying solely on symptom-based diagnosis can risk overlooking other conditions [12–13]. Ultimately, test selection depends on physician judgment and resource availability. [14]
Development of IBS
The pathogenesis and pathophysiology of IBS are not yet fully understood. It is a multifactorial process involving several contributing factors, such as impaired communication along the gut-brain axis, immune dysfunction, alterations in gut flora, food intolerances, and genetic predisposition. It remains unclear which of these factors trigger the onset of IBS and which exacerbate its symptoms in certain individuals. [15]
The role of the gut-brain axis in the development of IBS
One of the most widely accepted explanations for IBS is dysfunction in the gut-brain axis [1]. All four layers of the intestinal wall are densely supplied with blood vessels and nerves and contain approximately 100 million nerve cells, forming the enteric nervous system. This system is in constant two-way communication with the central nervous system (the brain and spinal cord), meaning that central nervous system overload (e.g., stress, anxiety, or sleep deprivation) can manifest as painful muscular contractions in the intestinal wall. These altered contractions affect intestinal motility, leading to either diarrhoea or constipation. If the contractions affect a small segment of the intestine, the contents become stuck and dry, causing constipation. If a longer segment is involved, contents pass too quickly, preventing water reabsorption and resulting in diarrhoea. [16]
Gut-brain axis dysfunction also contributes to visceral hypersensitivity, a hallmark of IBS. This condition causes the intestinal tract to respond with exaggerated pain to normal stimuli (such as gas or bloating), meaning the pain threshold is abnormally low for colonic distension. [3], [15]
These issues are closely linked to stress responses and psychological symptoms. According to a 2021 meta-analysis, depression and severe anxiety occur 40% more frequently in individuals with IBS [17]. The hypothalamic-pituitary-adrenal (HPA) axis, involved in stress response, may become hyperactive and secrete certain hormones abnormally (e.g. coretisol), altering gut motility, increasing visceral sensitivity, triggering immune responses, and disturbing gut flora. This process can also work in reverse: stress and anxiety may be consequences of gut dysfunction, such as low-grade inflammation, increased intestinal permeability, or imbalances in the microbiome. [15], [18]
Figure 3. Central nervous system overload (e.g., stress, anxiety, or sleep deprivation) causes painful muscular contractions in the intestinal wall
The role of the gut microbiome in the development of IBS
The gut microbiome is a complex ecosystem made up of bacteria, archaea, fungi, and viruses. It influences brain function by directly or indirectly interacting with the enteric nervous system and, through it, the gut-brain axis. [1]
The gut microbiome in people with IBS differs from that of healthy individuals, though findings vary between studies. These inconsistencies may stem from the variability between IBS subtypes and individual differences, as well as the relative novelty of this field. However, common findings include reduced microbial diversity, overgrowth of Proteobacteria, Veillonella, and certain Firmicutes, and a reduction in Bacteroidetes, Bifidobacteria, Lactobacilli, and methane-producing bacteria. [15], [19–20]
Dysbiosis—an imbalance in the gut microbial community—can lead to increased intestinal permeability. This may result from bacterial toxins, inflammatory mediators, or reduced production of short-chain fatty acids. In this so-called “leaky gut,” pathogens, toxins, or undigested food particles can penetrate the thin, fibrous connective tissue layer beneath the intestinal epithelial cells and enter the bloodstream. Their antigens trigger pro-inflammatory cytokines (e.g., IL-6, IL-8, TNF-α) via immune cells in the enteric nervous system, leading to low-grade inflammation that affects neurons in both the gut and the brain. This inflammation raises cortisol levels, potentially causing anxiety and concentration issues [1]. These psychological symptoms can then worsen IBS symptoms via the stressed gut-brain axis.
Figure 4. Dysbiosis refers to a disruption in the optimal balance and composition of the microbial community, during which the permeability of the intestinal mucosa increases.
Dysbiosis can also lead to small intestinal bacterial overgrowth (SIBO) under certain conditions [21]. One study found that 75% of IBS patients (157 of 202) tested positive for lactulose hydrogen breath tests, indicating SIBO [22]. Given the high prevalence, SIBO may be worth investigating as a more specific, treatable condition.
Approximately 10% of IBS cases are triggered by acute infectious gastroenteritis [23]. Individuals with genetic variants related to innate immunity and mucosal barrier function—as well as those with high stress or anxiety—are at increased risk of developing post-infectious IBS. This form typically presents as diarrhoeal IBS. Substances released during the infection also increase intestinal permeability. [24]
The role of food allergies and sensitivities in the development of IBS
Diet plays a key role in IBS pathogenesis by influencing the gut microenvironment, reducing colonic fermentation, and modulating immune activation, which can induce low-grade inflammation [25]. The role of food allergy and intolerance in IBS, however, is not fully understood. While true food allergies are rarely responsible, many patients report symptom exacerbation after consuming certain foods or drinks [26]. For instance, even with a negative celiac disease test, some individuals experience IBS symptoms after consuming gluten—suggesting an overlap with non-celiac gluten sensitivity [27]. Many IBS sufferers are sensitive to FODMAPs, and inadequate digestion of gluten and proteins like casein (from milk) can increase inflammation and stimulate the innate immune system. IgE and IgG receptors on mast cells can respond to these foods by releasing histamine and other inflammatory mediators, affecting various systems including the skin, nervous system, cardiovascular and respiratory tracts, and gastrointestinal system. These immune responses may lead to IBS symptoms, especially abdominal pain triggered by food sensitivities or allergies. [28]
Genetic predisposition to IBS
IBS is more common in families with multiple affected members, suggesting a genetic component, although environmental factors play a predominant role [29]. The genetic risk can range from complex polygenic inheritance—where various common genetic variants interact—to cases involving a single rare gene mutation. For example, mutations in the SC5NA gene, which encodes sodium ion channels, have been associated with abdominal pain in IBS. Additionally, polymorphisms in genes involved in serotonin signalling, immune regulation, and mucosal barrier function have also been linked to IBS pathogenesis. [15]
The role of microbial neurotransmitters and metabolites in the development of IBS
Although IBS is not classified as a typical inflammatory bowel disease, several studies have shown low-grade inflammation in the digestive tract, marked by increased numbers of enterochromaffin cells, intraepithelial lymphocytes, and mast cells [30]. Neurotransmitters produced by these cells—as well as by gut microbiota—play a significant role in IBS symptom development [1], [31]. Additionally, microbial metabolites influence essential gut functions, and an altered metabolic profile of gut bacteria may contribute to IBS symptoms [1], [32]. The neurotransmitters and metabolites listed below are of paramount importance in the development and progression of IBS:
Figure 5. Certain microbial metabolites influence key physiological processes in the gut, meaning that an altered metabolic profile of gut bacteria may also contribute to the symptoms of IBS.
Treatments of IBS
Challenges in the management of IBS
Managing IBS can be complex, but symptom relief is achievable. Many people with IBS consult multiple healthcare providers without success. Practitioners often struggle to diagnose and identify the root cause, while patients frequently feel dissatisfied with their care. Treatment outcomes depend greatly on the attitudes of both professionals and patients, the severity of comorbidities and symptoms, and persistent misconceptions surrounding the condition. [47]
For physicians, IBS can be a source of frustration—partly due to the absence of standardized treatment protocols. Some doctors may also believe that the condition is driven more by the patient’s psychological state than by clinical treatment, which can lead to disconnects in the doctor-patient relationship when patients don’t share this view. [48]
Ideally, a multidisciplinary team—comprising, for example, an internist, nutritionist, and psychologist or psychiatrist—can offer long-term, collaborative support. For successful management, the patient must take an active role, as lifestyle changes are a critical part of the process. [49–50]
Figure 6. Treatments of IBS
Medication for IBS
IBS symptoms can be managed with conventional medical treatments. Depending on the subtype of IBS, different medications may be prescribed. Laxatives are primarily used for constipation-predominant IBS, while antidiarrheals are used for diarrhoea-predominant IBS. [4]
Antispasmodics can relieve pain and cramps in some IBS patients [51]. These fall into two categories: 1. Neurotropic antispasmodics, which act on the nervous system to inhibit smooth muscle contractions (e.g., hyoscine butylbromide). 2. Musculotropic antispasmodics, which act directly on muscle tissue to reduce spasms (e.g., mebeverine), and may also help in constipation-predominant IBS. [6], [52]
Research on antidepressants in IBS has yielded mixed results [53]. Tricyclic antidepressants appear to be especially effective for diarrhoea-predominant IBS, while selective serotonin reuptake inhibitors may help more with constipation-predominant IBS. Serotonin-norepinephrine reuptake inhibitors are less commonly used however, they have shown promising results [52], [54]. These medications can relieve IBS symptoms even in patients without depression, and often at lower doses than typically used for mood disorders. [53]
Antibiotics are gaining attention in IBS treatment, especially given the emerging role of the gut microbiota. In some cases, particularly where SIBO is also present (mainly in diarrhoeal IBS), antibiotics may help by reducing the population of harmful gut bacteria. Treatment is usually short-term but may require repetition, and should always be medically supervised [55–56]. While antibiotics can reduce abnormal bacterial overgrowth, they may also deplete beneficial bacteria, potentially leading to other issues detectable through stool microbiome testing.
Chronic use of proton pump inhibitors (PPIs) to reduce stomach acid can also disrupt the microbiome, lowering bacterial diversity and promoting pathogenic overgrowth. PPI use has been linked to SIBO, which may contribute to IBS symptoms. [57]
The treatment of IBS with diet and nutritional supplements
Nutritional factors play a crucial role in managing IBS. For example, fibre intake can both alleviate and worsen symptoms. Short-chain, soluble, and highly fermentable fibres (such as oligosaccharides) can lead to rapid gas production, causing bloating and abdominal discomfort. In contrast, long-chain, viscous, soluble fibres with moderate fermentability—like psyllium—tend to produce less gas and may improve overall symptoms and relieve constipation. [58]
The low-FODMAP diet is one of the most commonly used dietary approaches for IBS. It involves reducing fermentable carbohydrates that are poorly absorbed in the small intestine and lead to gas formation. This diet has been shown to reduce symptoms by easing pressure on the gut wall, which is especially important for individuals with visceral hypersensitivity. However, long-term adherence can be difficult and may negatively impact gut microbiota diversity. [59–60]
Many IBS patients (due to suspected or confirmed food intolerances) follow other elimination diets that exclude common allergens [5], [61]. While such diets may offer short-term symptom relief, prolonged dietary restrictions are not always advisable, as they can further reduce microbiome diversity. Professional guidance is recommended to maintain nutritional balance. [5]
Simple practices like eating meals at regular times can help regulate bowel function [1], [13]. The effects of meal skipping or intermittent fasting vary by IBS type and individual physiology. These practices may be beneficial for some, but could worsen symptoms for others, so professional consultation is advised before adopting them. [62]
Many individuals with IBS also turn to herbal remedies. For example, aloe vera is often used for constipation-predominant IBS, although more scientific research is needed to confirm its effectiveness. Peppermint oil, on the other hand, has been shown to relieve abdominal pain and bloating, particularly in diarrhoea-predominant IBS [13], [63]. Enteric-coated peppermint oil capsules slowly release the active ingredient in the small intestine, helping to reduce bloating and pain during defecation [1]. Vitamin D and vitamin B6 supplementation can also support symptom management, given their roles in gut health and inflammation control, as previously discussed. [1]
A promising and evolving area is the use of probiotics in IBS treatment. Probiotics are beneficial bacteria found in certain foods and supplements that help restore gut microbiome balance. They may: normalize inflammatory cytokine levels, improve gut motility, reduce intestinal permeability, inhibit the overgrowth of fermentative bacteria in the small intestine [64]. Specific strains of probiotics have been shown to alleviate different symptoms. For example: Bifidobacterium breve, B. longum, and Lactobacillus acidophilus may reduce abdominal pain. Lactobacillus plantarum may relieve bloating. [56], [65]
While probiotics hold promise, their effectiveness varies between individuals. More research is needed to identify optimal strains and dosages. Fecal genome testing offers a personalized approach by providing a detailed view of an individual’s gut microbiome, allowing for tailored probiotic therapy.
IBS and psychological well-being
Given IBS’s multifactorial nature and its close links with the gut-brain axis and HPA axis, psychological factors are gaining increasing attention in IBS management.
As part of lifestyle changes, stress reduction is key. Relaxation techniques (such as autogenic training), meditation, regular physical activity, and exercise can all help decrease the frequency and severity of IBS symptoms. Exercise also improves mood and supports intestinal motility. Activities like cycling have been shown to reduce bloating and gas, while yoga has been found to ease symptoms by influencing the parasympathetic and sympathetic nervous systems. [13]
Psychological therapies, including psychoeducation, cognitive behavioural therapy, and gut-directed hypnotherapy, may offer further benefits. Although current evidence isn’t yet strong enough to recommend these approaches as standalone first-line treatments, clinical guidelines suggest them for patients who do not respond adequately to medication. [66]
In summary, while more research is needed to confirm the effectiveness of psychotherapeutic and alternative approaches, existing evidence indicates that addressing psychological factors and managing stress can play a significant role in relieving IBS symptoms and improving quality of life.
References
[1] ‘Biovis_Reizdarmsyndrom_EN.pdf’ https://www.biovis.eu/wp-content/uploads/Biovis_Reizdarmsyndrom_EN.pdf
[2] ‘Irritable bowel syndrome (IBS)’, nhs.uk, Oct. 24, 2017 https://www.nhs.uk/conditions/irritable-bowel-syndrome-ibs/
[3] ‘What Is Irritable Bowel Syndrome (IBS)?’, Cleveland Clinic https://my.clevelandclinic.org/health/diseases/4342-irritable-bowel-syndrome-ibs
[4] ‘Irritable bowel syndrome – Symptoms and causes’, Mayo Clinic https://www.mayoclinic.org/diseases-conditions/irritable-bowel-syndrome/symptoms-causes/syc-20360016
[5] P. Moayyedi et al., ‘Irritable bowel syndrome diagnosis and management: A simplified algorithm for clinical practice’, United Eur. Gastroenterol. J., vol. 5, no. 6, pp. 773–788, Oct. 2017, DOI: https://doi.org/10.1177/2050640617731968
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