E2 ModeratePreliminaryPEM not requiredCross-SectionalPeer-reviewedReviewed
Standard · 3 min
Brain Fog in Gastrointestinal Disorders: Small Intestinal Bacterial Overgrowth, Gastroparesis, Irritable Bowel Syndrome.
El Halabi, Maan, Arwani, Remy, Rao, Satish C et al. · Journal of clinical gastroenterology · 2025 · DOI
Quick Summary
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.
Why It Matters
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.
Observed Findings
54% (55/102) of patients undergoing SIBO breath testing reported brain fog symptoms.
Brain Fog Questionnaire scores were significantly higher in patients with reported brain fog (38.2±15.6) versus those without (10.9±9.4, p=0.001).
Patients with brain fog were more likely to use probiotics and proton pump inhibitors (p=0.04 for both).
Gastroparesis was significantly more common in patients reporting brain fog (p=0.01).
Irritable bowel syndrome showed increased prevalence in the brain fog group (p=0.05).
Inferred Conclusions
Brain fog is a prevalent symptom in patients with common gastrointestinal disorders, affecting over half the study population.
The association between gastroparesis, IBS, and brain fog suggests GI dysfunction may contribute to cognitive symptoms independent of SIBO status.
The Brain Fog Questionnaire may be a useful clinical tool for quantifying brain fog severity in GI populations.
Remaining Questions
Does gastroparesis or IBS directly cause brain fog, or do they share common underlying mechanisms (e.g., inflammation, dysbiosis, or altered gut–brain signaling)?
What is the mechanistic relationship between probiotic use and reported brain fog—do probiotics help or exacerbate symptoms, and in which patient subgroups?
What This Study Does Not Prove
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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How do the GI findings in this cohort compare to ME/CFS populations, and is the Brain Fog Questionnaire valid and sensitive for ME/CFS-related cognitive dysfunction?
What role do factors other than bacterial overgrowth (e.g., intestinal permeability, immune activation, or medication side effects) play in the brain fog observed?