Brain Fog in Gastrointestinal Disorders: Small Intestinal Bacterial Overgrowth, Gastroparesis, Irritable Bowel Syndrome.

Publication date: Oct 01, 2025

Brain fog (BF) is a term used to describe difficulties with concentration, memory, and overall mental clarity. Links of BF to chronic fatigue syndrome and COVID-19 have been described, as well as recently to small intestinal bacterial overgrowth (SIBO) and probiotics. To investigate the association between BF, SIBO, intestinal methanogen overgrowth (IMO), gastrointestinal (GI) medications, and specific GI disorders [irritable bowel syndrome (IBS) and gastroparesis] by utilizing a questionnaire to help diagnose BF. Patients undergoing lactulose breath testing (LBT) for clinical assessment of SIBO filled out a demographic questionnaire, including an inquiry about the presence of BF, a symptom questionnaire (PAGI-SYM), and a BF Questionnaire (BFQ; 20 BF symptoms rated never=0 to always=4, total score 0 to 80). A total of 102 patients underwent LBT, with the most common indication being bloating (67%), of whom 55 (54%) reported BF. The BFQ score was significantly higher in patients reporting BF than those not [38. 2+/-15. 6 vs. 10. 9+/-9. 4 (SEM) ( P =0. 001)]. Patients with BF were more likely to be on probiotics and proton pump inhibitors compared with those without BF ( P =0. 04). There was no major difference in the use of narcotics, prokinetics, or prebiotics. Gastroparesis and IBS were more common in patients who reported BF ( P =0. 01 and 0. 05, respectively), but not SIBO or IMO by breath testing. BF was observed in over one-half of patients with common GI disorders. The prevalence of BF was higher in patients on probiotics and those with gastroparesis and IBS. The BFQ may be useful to diagnose and quantify BF severity.

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