El Halabi, Maan, Arwani, Remy, Rao, Satish C et al. · Journal of clinical gastroenterology · 2025 · DOI
This study looked at brain fog—difficulty concentrating, remembering things, and thinking clearly—in patients with common digestive problems. Researchers surveyed 102 patients undergoing breath tests for bacterial overgrowth and found that over half reported brain fog. Those taking probiotics or with gastroparesis (slow stomach emptying) or irritable bowel syndrome were more likely to have brain fog.
Many ME/CFS patients experience both gastrointestinal symptoms and cognitive dysfunction ('brain fog'). This study provides early evidence that GI disorders, independent of SIBO positivity, correlate with brain fog severity, suggesting multiple potential pathways connecting gut and brain dysfunction that warrant investigation in ME/CFS populations.
This cross-sectional study cannot establish causation—it does not prove that gastroparesis or IBS causes brain fog, only that they co-occur. The lack of association between breath-test-confirmed SIBO/IMO and brain fog does not rule out pathogenic bacterial role, as breath testing may have limited sensitivity or pathogenic mechanisms may be unrelated to bacterial load. The study does not establish whether probiotics improve or worsen brain fog despite their association with increased reporting.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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