You cannot think straight. Words slip away mid-sentence. You read the same paragraph three times and retain nothing. You walk into a room and forget why you came. You feel — underneath the gut symptoms, underneath the fatigue — like something is wrong with your brain.
If you have IBS and you recognize this, you are not imagining it. And you are not losing your mind.
What you are experiencing has a name — brain fog — and it is increasingly recognized as a genuine feature of IBS, not a separate problem happening alongside it. The same dysregulated gut-brain system driving your digestive symptoms is affecting your cognitive function. Understanding why changes how you approach both.
The Gut-Brain Connection and Cognition
The gut and brain communicate through the gut-brain axis — a network of nerve pathways, immune signals, and hormones in constant bidirectional exchange. Most people know this affects digestion and mood. What is less widely known is that it also affects cognitive function: attention, memory, processing speed, and mental clarity.
Approximately 95 percent of the body’s serotonin — a neurotransmitter critical for mood, but also for cognition and gut motility — is produced in the gut (Yano et al., 2015). When the gut microbiome is disrupted, when the enteric nervous system is in a state of heightened reactivity, when chronic stress is flooding the system with cortisol, serotonin production and signaling are affected. And serotonin disruption is associated with the kind of cognitive symptoms IBS sufferers describe.
Chronic cortisol elevation — which accompanies the sustained stress response of IBS — also directly affects the hippocampus, the brain region central to memory and information processing (Konturek et al., 2011). A nervous system that has been under prolonged strain produces a brain that is genuinely less able to think clearly. This is not weakness. It is physiology.
What the Research Shows
Research on cognitive function in IBS is a growing area. Studies consistently find that people with IBS perform differently on cognitive assessments — particularly in areas of attention, working memory, and processing speed — compared to people without IBS (Guo et al., 2025).
Importantly, cognitive symptoms tend to be worst during or after flares — which is consistent with the mechanism. A gut in a heightened state of reactivity is sending more distress signals upward, activating more stress response, producing more cortisol, and leaving less cognitive resource available for clear thinking.
The brain fog of IBS is not a separate neurological condition. It is the cognitive expression of the same gut-brain dysregulation producing the physical symptoms.
The Fatigue-Fog Cycle
Brain fog in IBS rarely travels alone. It almost always comes accompanied by fatigue — the bone-deep exhaustion that goes beyond what sleep explains. This makes sense when you understand what the nervous system is doing: running a sustained, low-grade emergency response that consumes significant metabolic resources.
The HPA axis activation of chronic IBS stress is physiologically expensive. The constant gut monitoring, the anticipatory anxiety, the physiological preparation for threat that never fully resolves — all of it draws on the same resources that power clear thinking and sustained energy. Brain fog is, in part, the experience of a nervous system that has been working too hard for too long.
What Helps
Because brain fog in IBS shares its mechanism with the gut symptoms themselves, the approaches that address the gut-brain system help both simultaneously.
Gut-directed hypnotherapy and MBSR both directly support the parasympathetic nervous system restoration that chronic IBS stress depletes — and both show downstream improvements in cognitive symptoms alongside gut symptom reduction (Adler et al., 2025; Altobelli et al., 2022). Gut-directed CBT addresses the hypervigilance and catastrophizing that keep the HPA axis running at high cost (Lackner et al., 2018).
Sleep matters enormously. Even short-term sleep disruption impairs cognitive function significantly, and IBS disrupts sleep reliably. Addressing the sleep-gut loop — as both a gut intervention and a cognitive one — is one of the highest-yield things available.
The brain fog of IBS is real. It is not permanent. And addressing your gut-brain system treats it at its source.
About the author
Susan Liddy, MAMFT is a GI Psychotherapist and doctoral candidate in Integrative Health, specializing in nervous system-informed care for IBS and disorders of gut-brain interaction. Georgia residents are welcome to schedule a free consultation at www.susanliddy.com.
For educational purposes only. Not medical or psychological advice. Susan Liddy, MAMFT
References
Adler, E. C., Levine, E. H., Ibarra, A. N., Boparai, E. S., Hung, Y.-Y., McCrary, Q. D., & Lee, J. K. (2025). Gut-directed hypnotherapy for irritable bowel syndrome: A systematic review and meta-analysis. Neurogastroenterology & Motility, 37(4), e70037. https://doi.org/10.1111/nmo.70037
Altobelli, E., Angeletti, P. M., Profeta, V. F., & Petrocelli, R. (2022). Meditation and irritable bowel syndrome: A systematic review and meta-analysis. Journal of Clinical Medicine, 11(21), 6516. https://doi.org/10.3390/jcm11216516
Guo, Y., Huang, X., Liao, Y., Lin, Y., Chen, S., Zeng, Y., & Chen, J. (2025). Cognitive impairment in IBS: A narrative overview. Journal of Gastrointestinal and Liver Diseases, 34(1), 122–127. https://doi.org/10.15403/jgld-5800
Konturek, P. C., Brzozowski, T., & Konturek, S. J. (2011). Stress and the gut: Pathophysiology, clinical consequences, diagnostic approach and treatment options. Journal of Physiology and Pharmacology, 62(6), 591–599.
Lackner, J. M., Jaccard, J., Keefer, L., Brenner, D. M., Firth, R. S., Gudleski, G. D., Hamilton, F. A., Katz, L. A., Krasner, S. S., Ma, C.-X., Radziwon, C. D., & Sitrin, M. D. (2018). Improvement in gastrointestinal symptoms after cognitive behavior therapy for refractory irritable bowel syndrome. Gastroenterology, 155(1), 47–57. https://doi.org/10.1053/j.gastro.2018.03.063
Yano, J. M., Yu, K., Donaldson, G. P., Shastri, G. G., Ann, P., Ma, L., Nagler, C. R., Ismagilov, R. F., Mazmanian, S. K., & Hsiao, E. Y. (2015). Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell, 161(2), 264–276. https://doi.org/10.1016/j.cell.2015.02.047
