Irritable Bowel Syndrome (IBS) is a gastrointestinal disorder characterized by a dysfunction in gut-brain interaction. It is defined by symptoms such as abdominal pain, which is often associated with changes in stool form or frequency. This condition affects between 5% and 10% of otherwise healthy individuals at any one point in time and, in most people, follows a pattern of flare-ups and periods of symptom relief.
The primary cause of IBS is disordered communication between the gut and the brain, leading to alterations in gut motility, visceral hypersensitivity, and altered central nervous system (CNS) processing. The exact pathophysiology of IBS is not fully understood and is considered multifactorial. Genetic factors, diet, abnormalities in the gut microbiome, infections, and psychological factors all contribute to the modulation of the bi-directional gut-brain axis, which is thought to play a central role in the development and progression of IBS.
Dietary advice is a cornerstone in managing Irritable Bowel Syndrome (IBS) and is recommended as a first-line treatment by the British Society of Gastroenterology. Elimination diets, such as the low-FODMAP diet, the Mediterranean diet, gluten-free diets, and traditional guidance to eat small, regular meals while avoiding trigger foods, alcohol, and caffeine, have been shown to significantly improve IBS symptoms. This is because diet is one of the most effective ways to alter the gut microbiota. A diverse, nutrient-rich diet supports microbial growth, while a nutrient-poor diet can lead to intestinal dysbiosis, characterized by a reduction in beneficial bacteria and an overgrowth of pathogenic species.
In patients with visceral hypersensitivity, such as in IBS, fermentable carbohydrates (oligosaccharides, disaccharides, monosaccharides,and polyols) like FODMAPs increase intestinal water content and colonic volume, causing osmotic diarrhea, gas production, and abdominal distension. Reducing FODMAPs can relieve these symptoms. Similarly, gluten-free diets benefit many IBS patients by reducing fructans, a type of FODMAP. Gluten-containing foods can also increase intestinal permeability and immune activation by increasing the expression of immunemarkers,( toll-like receptor 2, and regulated T-regulatory cell marker, forkhead box P3 protein), contributing to IBS symptoms.
Western diets, rich in processed and fatty foods, reduce gut microbial diversity, while high-fiber diets support the growth of beneficial bacteria. Dietary fiber promotes the production of short-chain fatty acids (SCFAs) like butyrate, which are essential for gut health. SCFAs strengthen the gut barrier, reduce inflammation, and regulate feeding behavior and energy balance. Diets rich in fiber, phytochemicals, and probiotics can help restore microbial diversity and improve gut function.
Treatment for IBS should be personalized based on the subtype. For IBS with diarrhea (IBS-D), the focus is on reducing bowel movements, while for IBS with constipation (IBS-C), the goal is to promote regular bowel movements. Patients are advised to eat smaller meals, avoid gas-producing foods, and limit alcohol, fat, and spicy foods. The Mediterranean diet, featuring olive oil (which contains around 30 phenolic compounds), fresh produce, whole grains, nuts, and moderate amounts of fish, poultry, and dairy, is particularly beneficial due to its anti-inflammatory and gut-supportive properties.
It is crucial to consider individual dietary needs and cultural or ethnic differences when tailoring IBS treatment. Personalized dietary approaches can help patients manage symptoms effectively while maintaining a balanced and enjoyable diet.
I find these mechanisms fascinating to read about, as it offers a deeper insight into the root causes of diseases and helps clarify the reasoning behind the treatments (pharmaceutical and non-pharmaceutical)
Cause of IBS:Stress: The amygdala, located in the central nervous system (CNS), plays a crucial role in the response to anxiety. This structure activates the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system when patients find themselves in anxious situations. Chronic anxiety increases the activity of the amygdala, leading to dysregulation of the HPA axis, which ultimately results in visceral hyperalgesia. Visceral hypersensitivity is considered one of the primary factors contributing to symptoms in individuals with irritable bowel syndrome (IBS).
Post-infectious IBS: Between 3% and 35% of patients with gastrointestinal (GI) infections develop IBS symptoms three to twelve months following the infection. A rise in mucosal inflammatory cells, particularly mast cells, has been observed in various parts of the small intestine and colon. The release of mediators such as nitric oxide, interleukins, histamine, and proteases stimulates the enteric nervous system, leading to impairments in motility, secretion, and hyperalgesia in the GI tract.
The Role of Bacterial Flora in IBS: While there are a limited number of bacteria, such as Lactobacillus and Enterococci, in the stomach and upper parts of the large intestine, microbial populations increase dramatically in the distal parts of the GI tract, reaching up to 10¹² per milliliter. Changes in the quantity and quality of these bacteria can have selective effects on sensory and motor dysfunctions. These effects can be influenced by bile acid malabsorption, mucosal irritation and inflammation, as well as increased food fermentation and gas production.
Genetics: Several studies have shown that genetic factors play a role in the prevalence of IBS. Family members of individuals with IBS often experience similar GI complaints. IBS is twice as prevalent among monozygotic (identical) twins compared to dizygotic (fraternal) twins.
References:
Jayasinghe, Maleesha & Karunanayake, Vinuri & Mohtashim, Ali & Caldera, Dilushini & Mendis, Piyalka & Prathiraja, Omesh & Rashidi, Fatemeh & Damianos, John. (2024). The Role of Diet in the Management of Irritable Bowel Syndrome: A Comprehensive Review. Cureus. 16. 10.7759/cureus.54244.
Enck, P., Aziz, Q., Barbara, G. et al. Irritable bowel syndrome. Nat Rev Dis Primers 2, 16014 (2016). https://doi.org/10.1038/nrdp.2016.14
H Vahedi1 , R Ansari1 , MM Mir-Nasseri1 , E Jafari1. (2010). Irritable Bowel Syndrome: A Review ArticleMiddle. East Journal of Digestive Diseases.Vol.2 . No.2.
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