Irritable bowel syndrome (IBS) is a chronic disorder of the microbiota–gut–brain axis involving abdominal pain, altered bowel habits, visceral hypersensitivity, low-grade inflammation, impaired intestinal barrier function, and altered gut microbiota. Many studies show microbiota differences between IBS and healthy controls, but no single “IBS signature” or clear “healthy microbiota” definition has emerged due to high variability and inconsistent methods. Microbiota-targeted strategies such as the low FODMAP diet and fecal microbiota transplantation (FMT) can relieve symptoms in some patients, but results are mixed, long-term safety is uncertain, and both may affect microbial diversity and gut integrity.

To better understand IBS, researchers are combining molecular biology, advanced neuroimaging, microbiome analysis, and data science. MRI studies show reproducible changes in brain regions tied to pain and emotion, and emerging “radiomicrobiomics” links brain imaging with microbiota and metabolite data. Microbiome work is moving toward more standardized methods, metagenomics for species- and function-level detail, and richer metadata (diet, BMI, age, sex, medications) to reduce confounding. The authors conclude that multimodal, longitudinal, interdisciplinary studies integrating gut microbiota, barrier function, immune markers, neuroimaging, and clinical outcomes are essential to clarify causality in the microbiota–gut–brain axis and to guide more personalized IBS treatments.

Reference: Hillestad EMR, van der Meeren A, Nagaraja BH, et al. Gut bless you: The microbiota-gut-brain axis in irritable bowel syndrome. World J Gastroenterol. 2022 Jan 28;28(4):412-431. doi: 10.3748/wjg.v28.i4.412. PMID: 35125827; PMCID: PMC8790555.

Irritable bowel syndrome (IBS) is a common functional GI disorder defined by recurrent abdominal pain with altered bowel habits, diagnosed by Rome IV criteria and classified into IBS-C, IBS-D, IBS-M, and IBS-U. It affects about 4% of the population, is more common in women, and significantly impairs quality of life. Its pathophysiology is heterogeneous, involving altered motility, visceral hypersensitivity, small intestinal bacterial overgrowth, diet, and gut dysbiosis. The gut microbiota—dominated by Firmicutes and Bacteroidetes—supports digestion, immunity, and gut–brain signaling. In IBS-C, studies show altered bacterial profiles and increased methanogens (e.g., Methanobrevibacter smithii), with methane linked to slower transit and more severe constipation.

Management of IBS-C relies heavily on diet and microbiota-focused strategies, but no single “ideal diet” exists. First-line care emphasizes general healthy eating, fluids, exercise, and symptom-targeted changes. Low-FODMAP diets can reduce bloating and global IBS symptoms but have stronger evidence in IBS-D, possible adverse microbiota effects, and uncertain long-term safety. In IBS-C, soluble fibers (psyllium, oats, inulin) can improve stool frequency and consistency, while insoluble fibers may worsen discomfort. Functional foods (kiwi, figs, prunes, linseeds), prebiotics, probiotics, and symbiotics show promising but mixed benefits on constipation, bloating, and quality of life, and fecal microbiota transplantation remains experimental. More high-quality, subtype-specific studies are needed to define optimal nutritional and microbiota-modulating approaches for IBS-C.

8Reference: Di Rosa C, Altomare A, Terrigno V, et al. Constipation-Predominant Irritable Bowel Syndrome (IBS-C): Effects of Different Nutritional Patterns on Intestinal Dysbiosis and Symptoms. Nutrients. 2023 Mar 28;15(7):1647. doi: 10.3390/nu15071647. PMID: 37049488; PMCID: PMC10096616.

The American College of Gastroenterology's (ACG) 2009 monograph on irritable bowel syndrome (IBS) is an evidence-based update that defines IBS as abdominal pain or discomfort with altered bowel habits for at least 3 months, without structural or biochemical abnormalities. The ACG Task Force on IBS used systematic reviews and a formal grading system (Grade 1/2; evidence levels A–C) to assess diagnostic strategies and treatments. In patients under 50 with typical IBS symptoms and no alarm features, routine extensive testing is not recommended. Instead, limited evaluation plus celiac serology in IBS-D/IBS-M is advised, with colonoscopy reserved for those ≥50 or with alarm features (anemia, weight loss, family history of colorectal cancer/IBD/celiac).

Therapeutically, the review supports psyllium (but not wheat or corn bran) for global IBS symptoms, selected antispasmodics and peppermint oil for short-term pain relief, and loperamide for stool frequency/consistency rather than overall symptom control. Short courses of rifaximin and some nonabsorbable antibiotics benefit IBS-D and bloating, while certain probiotics—especially bifidobacteria or combinations—show modest efficacy. Alosetron (5-HT₃ antagonist) helps severe IBS-D but carries risks of constipation and ischemic colitis. Tegaserod (5-HT₄ agonist) improved IBS-C/M but was withdrawn over cardiovascular concerns. Lubiprostone is effective for IBS-C in women, and both TCAs and SSRIs improve global symptoms and pain across IBS subtypes. Psychological therapies (CBT, dynamic psychotherapy, hypnotherapy) also reduce global symptoms, whereas evidence for exclusion diets, herbal therapies, acupuncture, and SIBO testing is limited or inconsistent.

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Reference: American College of Gastroenterology Task Force on Irritable Bowel Syndrome, Brandt LJ, Chey WD, et al. An evidence-based position statement on the management of irritable bowel syndrome. Am J Gastroenterol. 2009 Jan;104 Suppl 1:S1-35. doi: 10.1038/ajg.2008.122. PMID: 19521341.