What is the root cause of IBS: Brehan Crawford, L.Ac., beside a gut-brain diagram

What Is the Root Cause of IBS?

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    IBS affects about 15% of Americans, and most of them have heard some version of the same sentence: there is no known cause, so learn to live with it. I see it differently. In traditional Chinese medicine, IBS has a pattern, a mechanism and a direction for treatment. The root of it is not in the bowel alone. It is in the conversation between your gut and your brain, and that conversation can be repaired.

    The short answer

    The root cause of IBS is a disruption of the gut-brain axis. Chinese medicine calls it a Liver-Spleen disharmony: your nervous system is stuck in fight or flight, and it talks over your gut. The fix is not a diarrhea pill. It is re-establishing a healthy connection between the gut and the brain.

    The short version, on video.

    Why don't doctors know what causes IBS?

    Doctors are not taught what causes IBS, even though it affects about 15% of Americans. That is why so many of my patients arrive having been told they will simply have to live with it. They were not dismissed out of carelessness. The model their doctor was trained in has no root cause to offer.

    The research on how IBS is handled in practice shows the gap clearly. In a survey of primary care providers in the United States and nine European countries, most saw IBS as a diagnosis of exclusion rather than a definite diagnosis, described it as moderately to extremely difficult to treat, and referred very few patients to anyone who works with the nervous system and stress side of the condition.[1] A study of 697 healthcare professionals scored their IBS knowledge at an average of 10.9 out of 30 and concluded that knowledge was inadequate.[2]

    Patients feel it. Among people who visited an IBS information website, almost all had seen a healthcare professional and tried some form of therapy, yet 96% still had moderate to severe symptoms, and only 41% believed their physician knew enough about IBS.[3] If that sounds like you, you are not imagining the problem, and you are not out of options. I teach the full picture of what is happening, and what to do about it, inside my community, Gut Brain Synchrony.

    Is IBS a gut-brain disorder?

    Yes. The root cause of IBS is a disruption of the gut-brain axis. Modern gastroenterology has moved toward this view as well: the Rome IV criteria, the international standard for diagnosing IBS, describe these conditions as disorders of gut-brain interaction, involving disturbed motility, a hypersensitive gut, altered immune function, altered gut microbes and altered processing in the central nervous system.[4]

    The axis runs both ways. Your gut has its own nervous system, the enteric nervous system, wired into the brain. Research on the gut-brain axis shows the gut microbes influence stress and pain systems and brain chemistry, and the brain in turn alters the microbes and their behavior through the autonomic nervous system.[5] A 12-year study that followed a random sample of Australian adults found that higher anxiety at the start predicted new gut disorders years later, and that people who started with a gut disorder went on to develop more anxiety and depression. Its conclusion was plain: the central nervous system and the gut interact in both directions.[6]

    This is why gut-only solutions keep falling short. If the signal coming down from the brain is distorted, the gut will keep responding to it.

    What is Liver-Spleen disharmony in Chinese medicine?

    In traditional Chinese medicine, IBS can be viewed as a Liver-Spleen disharmony. The Liver is responsible for the smooth, free flow of qi through the body, and it is the organ most affected by stress and frustration. The Spleen governs digestion: it transforms food into usable energy and moves fluids where they belong. When the Liver is tense and overloaded, it overacts on the Spleen. Classical texts describe this as Wood overacting on Earth. The result is the picture you know: cramping, urgency, bloating, stools that swing between loose and stuck, and symptoms that flare when life gets hard.

    This is not an obscure pattern. In a study of 383 IBS patients at a Chinese medicine hospital, 291 (76%) were diagnosed with Liver depression and Spleen deficiency, far more than any other pattern.[7] A 2026 review in the American Journal of Chinese Medicine went further and read Liver depression with Spleen deficiency in modern terms, as gut-brain axis dysfunction, describing the Chinese medicine principle of soothing the Liver and strengthening the Spleen as a way of working on that axis.[8]

    What happens when the Liver is overloaded?

    Your Liver regulates how stress hormones affect the enteric nervous system, and when it is overloaded, it changes how your digestive system works. The physiology lines up with that. Corticotropin-releasing factor, or CRF, is the hormone that starts the body's stress response. Research on CRF shows it stimulates the colon's enteric nervous system, increases intestinal permeability and makes the gut more sensitive to pain, acting through the autonomic nervous system and through CRF receptors in the gut wall itself.[9] In other words, stress chemistry lands directly on the bowel. That is the Liver overacting on the Spleen, described in the language of a laboratory.

    Why does stress cause IBS flare-ups?

    A Liver-Spleen disharmony means your nervous system is stuck in fight or flight, and it is talking over your gut. Digestion belongs to the rest-and-digest side of the nervous system. When the fight-or-flight side never stands down, the gut never gets the quiet signal it needs to work normally.

    You can measure this. When researchers gave the stress hormone CRH to 28 people with IBS and 34 healthy controls, the IBS group had a bigger stress-hormone (ACTH) response. Men with IBS had larger increases in colon movement, and women with IBS had lower resting parasympathetic tone, the calming side of the nervous system. Brain scans pointed to weaker top-down braking of the stress response from a region of the brain that normally keeps it in check.[10]

    Heart rate variability tells the same story. It is a simple measure of how flexibly your nervous system shifts between alert and calm. A meta-analysis found lower high-frequency heart rate variability, the parasympathetic component, in people with IBS than in healthy controls.[11] A larger analysis of 58 studies, including 1,005 people with IBS, found significantly lower parasympathetic markers across IBS, fibromyalgia and chronic fatigue syndrome.[12] The calming brake is weaker. The alarm is louder. The gut is caught in the middle.

    Gut Brain Synchrony

    Told to live with IBS? Learn to retrain the gut-brain connection instead.

    Gut Brain Synchrony is my community on Skool: courses on gut, brain and sleep health, condition-specific programs, and weekly live Q&A with our clinical team. It is where I teach the step-by-step version of this article, and where you can work with me directly. Your first week is free.

    Join Gut Brain Synchrony

    Why don't diarrhea pills fix IBS?

    Because they work on the symptom at the end of the chain, not the signal at the start of it. The solution to IBS is not to give you diarrhea pills. It is to re-establish a healthy connection between the gut and the brain.

    Even conventional reviews describe the limit. Antidiarrheal drugs such as loperamide reduce how often you go, but they have limited effects on pain relief.[13] The pain, the urgency and the flare that comes with a stressful week all come from the gut-brain loop, and that loop is still running. If you have tried everything for your gut and you are still bloated, I walk through more of the digestive side in why you can be bloated even when you eat healthy.

    How do you reset the gut-brain axis?

    In Chinese medicine the principle is to soothe the Liver and strengthen the Spleen. In modern terms, you lower the fight-or-flight signal, restore the calming side of the nervous system, and give the gut the steady conditions it needs. This is how I approach it.

    01 Turn up the calming nerve. The vagus nerve carries the rest-and-digest signal to the gut. In a randomized trial of 64 people with IBS or functional dyspepsia, two weeks of gentle vagus nerve stimulation at the ear reduced abdominal pain, how often it came, overall symptoms, anxiety and depression, and raised vagal activity. The higher the vagal activity at the end, the lower the pain.[14] Slow breathing with a long exhale works on the same nerve, and you can practise it every day.
    02 Use acupuncture to reset the pattern. In a multicenter trial of 531 people with IBS, 18 acupuncture sessions over six weeks lowered symptom severity scores by 123.5 points, against 94.7 points for standard medication, with the benefit lasting through 12 weeks of follow-up.[15]
    03 Soothe the Liver and strengthen the Spleen with herbs. Tong Xie Yao Fang is the classical formula written for exactly this pattern: pain and urgency driven by a tense Liver over a weak Spleen. A review of 11 randomized trials in 985 adults with diarrhea-predominant IBS found it outperformed both placebo and Western medication for overall symptom improvement, improved stool and pain against placebo, and did better than Western medication for quality of life and anxiety.[16] Formulas are chosen to fit your pattern, which is why I assess before I prescribe.
    04 Retrain the brain side of the loop. A 2025 network meta-analysis of 67 randomized trials and 7,441 people found that behavioural therapies aimed at the brain-gut connection, including cognitive behavioural therapy, self-management programs and gut-directed hypnotherapy, improved global IBS symptoms compared with waiting.[17] This is the gut-brain axis being treated from the top down.
    05 Eat on a rhythm, and eat warm. The Spleen likes regularity and warmth. In the study of 383 IBS patients, irregular meals were tied to the type of IBS, and skipping breakfast was tied to the Chinese medicine pattern.[7] Eat at steady times, sit down to eat, and favour cooked, warm food over cold and raw. My digestive health start-here guide covers the daily habits in more detail.
    06 Do it with support. Resetting a nervous system that has been on alert for years is not a one-week project. A guide, a group of people working on the same thing, and a clinician to ask make the difference between knowing what to do and actually doing it.

    Questions people ask about the cause of IBS

    What is the main cause of IBS-D?

    The same root as every type of IBS: a disrupted gut-brain axis. In Chinese medicine, diarrhea-predominant IBS is most often the Liver overacting on a weakened Spleen, the pattern found in 76% of patients in the study above.[7] Stress pushes the bowel to move too fast, and a weak Spleen cannot hold and transform what passes through.

    Can stress and anxiety cause IBS?

    They are part of the cause and part of the result. The 12-year study above showed anxiety predicting new gut disorders, and gut disorders predicting new anxiety.[6] That is why the work has to address both ends of the axis at once.

    Do I really have to learn to live with IBS?

    No. In traditional Chinese medicine there is a solution. When you understand IBS as a Liver-Spleen disharmony and a gut-brain axis problem, there is something specific to work on: calming the fight-or-flight signal, strengthening digestion, and rebuilding the connection between the two.

    Your gut is not broken. It is listening to a nervous system that has forgotten how to stand down, and that can be taught again.

    — Brehan Crawford, L.Ac.

    Gut Brain Synchrony

    Stop living around your IBS

    If you have been told there is nothing to do but manage the symptoms, start with the root. Inside you will find my gut guide, courses on the gut-brain connection, and weekly live Q&A where you can bring your questions to me and our clinical team.

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    References

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    2. Wang T, Wu C, Wang L, Tang Y. Knowledge, attitude, and practice of healthcare professionals towards irritable bowel syndrome: a multicenter, cross-sectional study. Sci Rep. 2024;14(1):29128. doi:10.1038/s41598-024-80680-z
    3. Van Malderen K, De Man JG, De Winter BY, De Schepper HU. Epidemiological characteristics of a population visiting a patient-centered informative website about irritable bowel syndrome. Acta Gastroenterol Belg. 2023;86(1):17-25. doi:10.51821/86.1.10885
    4. Drossman DA. Functional gastrointestinal disorders: history, pathophysiology, clinical features and Rome IV. Gastroenterology. 2016. doi:10.1053/j.gastro.2016.02.032
    5. Mayer EA, Tillisch K, Gupta A. Gut/brain axis and the microbiota. J Clin Invest. 2015;125(3):926-938. doi:10.1172/JCI76304
    6. Koloski NA, Jones M, Kalantar J, et al. The brain-gut pathway in functional gastrointestinal disorders is bidirectional: a 12-year prospective population-based study. Gut. 2012;61(9):1284-1290. doi:10.1136/gutjnl-2011-300474
    7. Hou ZK, Li M, Xie D, Liu FB. Traditional Chinese medicine syndrome distribution and neuroendocrine mechanisms of irritable bowel syndrome: cross-sectional study. Zhongguo Zhong Yao Za Zhi. 2016;41(7):1325-1337. doi:10.4268/cjcmm20160727
    8. Yu A, Bi Y, Xu X. Brain-gut axis perspective on irritable bowel syndrome: the role of gut microbiota and therapeutic strategies of traditional Chinese medicine. Am J Chin Med. 2026;54(7):2093-2122. doi:10.1142/S0192415X26500771
    9. Taché Y, Larauche M, Yuan PQ, Million M. Brain and gut CRF signaling: biological actions and role in the gastrointestinal tract. Curr Mol Pharmacol. 2018;11(1):51-71. doi:10.2174/1874467210666170224095741
    10. Kano M, Muratsubaki T, Van Oudenhove L, et al. Altered brain and gut responses to corticotropin-releasing hormone (CRH) in patients with irritable bowel syndrome. Sci Rep. 2017;7(1):12425. doi:10.1038/s41598-017-09635-x
    11. Sadowski A, Dunlap C, Lacombe A, Hanes D. Alterations in heart rate variability associated with irritable bowel syndrome or inflammatory bowel disease: a systematic review and meta-analysis. Clin Transl Gastroenterol. 2020;12(1):e00275. doi:10.14309/ctg.0000000000000275
    12. Vreijling SR, Troudart Y, Brosschot JF. Reduced heart rate variability in patients with medically unexplained physical symptoms: a meta-analysis of HF-HRV and RMSSD. Psychosom Med. 2021;83(1):2-15. doi:10.1097/PSY.0000000000000874
    13. Kim MC, Park Y, Lee HS. Treatment of irritable bowel syndrome with predominant diarrhea. Korean J Gastroenterol. 2025;85(2):105-109. doi:10.4166/kjg.2025.011
    14. Sun X, Lin Q, Xu Y, et al. Ameliorating effects and autonomic mechanisms of transcutaneous auricular vagus nerve stimulation on abdominal pain in patients with functional dyspepsia and irritable bowel syndrome. Neurogastroenterol Motil. 2026;38(9):e70224. doi:10.1111/nmo.70224
    15. Pei L, Geng H, Guo J, et al. Effect of acupuncture in patients with irritable bowel syndrome: a randomized controlled trial. Mayo Clin Proc. 2020;95(8):1671-1683. doi:10.1016/j.mayocp.2020.01.042
    16. Liang SB, Cao HJ, Kong LY, et al. Systematic review and meta-analysis of Chinese herbal formula Tongxie Yaofang for diarrhea-predominant irritable bowel syndrome. Front Pharmacol. 2022;13:904657. doi:10.3389/fphar.2022.904657
    17. Thakur ER, Khasawneh M, Moayyedi P, Black CJ, Ford AC. Efficacy of behavioural therapies for irritable bowel syndrome: a systematic review and network meta-analysis. Lancet Gastroenterol Hepatol. 2025;10(12):1075-1088. doi:10.1016/S2468-1253(25)00238-9