7 Causes of Irritable Bowel Syndrome, Explained by a Dietitian

Irritable Bowel Syndrome (IBS) affects approximately 11% of the global population, making it one of the most common gastrointestinal disorders in the world. Yet despite how widespread it is, IBS remains poorly understood by many — including some of the people living with it.

If you've been diagnosed with IBS, or suspect you might have it, understanding what's driving your symptoms is the first step toward managing them effectively. While the exact cause of IBS is not yet fully established, research has identified several key contributing factors.

Here are the 7 evidence-based causes of IBS — and what they mean for your gut health.

1. Gut Microbiota Dysbiosis

Your gut is home to trillions of microorganisms — collectively known as the gut microbiome — that play a vital role in digestion, immunity, and overall health. When this ecosystem becomes imbalanced (a state called dysbiosis), it can contribute to the development of IBS.

Research has shown that people with IBS tend to have a less diverse gut microbiome compared to healthy individuals. Specific changes — such as increased levels of Methanobrevibacter smithii and reduced levels of beneficial Bifidobacterium — have been consistently observed in IBS patients [1].

Want to understand this in more depth? Read our full guide on the gut microbiome and IBS.

2. Intestinal Inflammation

While IBS is classified as a functional disorder (meaning there's no visible structural damage), emerging research suggests that low-grade intestinal inflammation may play a role in many cases.

Studies have found elevated inflammatory markers in the blood and stool of IBS patients, as well as increased intestinal permeability (sometimes called "leaky gut") — a condition where the gut lining becomes more permeable, potentially allowing harmful substances to enter the bloodstream and trigger an immune response [2].

This helps explain why some people with IBS experience systemic symptoms like fatigue and brain fog alongside their digestive issues.

3. Food Intolerances & Dietary Triggers

Certain foods are a well-established trigger for IBS symptoms — particularly those high in FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols). These short-chain carbohydrates are poorly absorbed in the small intestine and fermented by gut bacteria, producing gas and drawing in water.

A low FODMAP diet has been shown in randomised controlled trials to improve symptoms in up to 75% of IBS patients [3]. However, it's a structured, 3-phase protocol that should be undertaken with the guidance of a trained dietitian to ensure it's done correctly and doesn't unnecessarily restrict your diet long-term.

Learn more in our beginner's guide: What Are FODMAPs? A Guide to the Low FODMAP Diet.

4. Post-Infectious IBS (Infection & Parasites)

Have you ever had a bout of gastroenteritis — a "stomach bug" — and noticed your gut was never quite the same afterwards? This is known as post-infectious IBS (PI-IBS), and it's more common than many people realise.

Following a gastrointestinal infection (bacterial, viral, or parasitic), some individuals develop lasting changes in their gut microbiome, increased intestinal permeability, and immune activation — all of which can trigger ongoing IBS symptoms [4]. PI-IBS accounts for a significant proportion of new IBS diagnoses.

5. Psychological Triggers & the Gut-Brain Axis

The gut and brain are in constant two-way communication via the gut-brain axis. This means that psychological stress, anxiety, and depression don't just affect your mood — they directly influence gut function, motility, and pain perception.

Research consistently shows that people with IBS have higher levels of psychological distress than the general population. Chronic stress can increase intestinal permeability, alter the gut microbiome, and activate the immune system — all of which worsen IBS symptoms [5]. Depression has also been identified as an independent risk factor for developing IBS.

This doesn't mean IBS is "all in your head" — it means the mind-gut connection is real and powerful. Read our evidence-based guide on stress management for IBS relief for practical strategies.

6. Prolonged Antibiotic Use

Antibiotics are sometimes necessary and life-saving — but their impact on the gut microbiome is significant. By killing harmful bacteria, antibiotics also disrupt beneficial bacterial populations, potentially leading to dysbiosis.

A population-based cohort study found that individuals who had received three or more courses of antibiotics had a significantly increased risk of developing IBS compared to those who had received fewer courses [6]. This highlights the importance of using antibiotics only when necessary and supporting gut health during and after antibiotic treatment.

7. Genetics

IBS tends to run in families, and research suggests there may be a genetic predisposition to the condition. Certain genetic variants have been associated with an increased risk of developing IBS, potentially influencing gut motility, visceral sensitivity, and immune function [7].

That said, genetics is rarely the sole driver — environmental factors, diet, stress, and the microbiome all interact with genetic predisposition to determine whether IBS develops and how severe it becomes. More research is underway to better understand the genetic underpinnings of IBS.

What Should You Do If You Have IBS?

Understanding the potential causes of your IBS is empowering — but knowing what to do about it is what really matters. The good news is that IBS is very manageable with the right approach. Key strategies include:

• Dietary management — following a structured low FODMAP diet under dietitian guidance
• Stress management — mindfulness, CBT, exercise, and quality sleep (see our stress management guide)
• Supporting your microbiome — through dietary diversity, prebiotics, and targeted probiotics
• Working with a specialist — an accredited dietitian with IBS expertise can personalise your approach and guide you through the low FODMAP process safely

For a comprehensive overview of IBS management, read our guide: What Is IBS? A Dietitian's Complete Guide.

Get a Complete, Dietitian-Designed IBS Management Plan

If you're ready to stop guessing and start managing your IBS with confidence, The IBS Program gives you everything you need in one place. Created by an accredited dietitian, it covers the low FODMAP diet, symptom tracking, meal planning, and lifestyle strategies — all tailored to help you identify your triggers and feel better, faster.

→ Explore The IBS Program and take the first step toward lasting gut health

References

[1] Bhattarai, Y., Muniz Pedrogo, D. A., & Kashyap, P. C. (2017). Irritable bowel syndrome: a gut microbiota-related disorder? American Journal of Physiology — Gastrointestinal and Liver Physiology, 312(1), G52–G62.

[2] Barbara, G., Cremon, C., & Stanghellini, V. (2019). Inflammatory bowel disease and irritable bowel syndrome: similarities and differences. Current Opinion in Gastroenterology, 35(1), 24–31.

[3] Halmos, E. P., et al. (2014). A diet low in FODMAPs reduces symptoms in patients with irritable bowel syndrome. Gastroenterology, 146(5), 67–75.

[4] Cash, B. D., Epstein, M. S., & Shah, S. M. (2019). A novel bioelectric impedance analysis for the assessment of intestinal inflammation in patients with post-infectious IBS. Neurogastroenterology & Motility, 31(6), e13571.

[5] Lackner, J. M., Gudleski, G. D., & Blanchard, E. B. (2004). Beyond abuse: the association among parenting style, abdominal pain, and somatization in IBS patients. Behaviour Research and Therapy, 42(9), 1099–1111.

[6] Lee, S. Y., et al. (2017). The association between antibiotics and new-onset irritable bowel syndrome: a population-based cohort study. Gut and Liver, 11(4), 565–572.

[7] Camilleri, M. (2018). Genetics and irritable bowel syndrome: from genomics to intermediate phenotype and pharmacogenetics. Gastroenterology Clinics, 47(1), 25–34.