Bloating and Brain Fog: Scientists Discover Links with SIBO

Bloating and brain fog

Gas, abdominal bloating, and distension are all common symptoms of gastrointestinal problems. Brain fog is a combination of symptoms such as mental confusion, impaired judgment, and poor short-term memory. It can also be associated with difficulty with concentration. Brain fog has been linked to other chronic disorders such as Postural Orthostatic Tachycardia Syndrome (POTS). The production of D-lactic acidosis has been linked to probiotic use. In this paper, scientists looked at whether SIBO (small intestinal bacterial growth), especially with D-lactic acid-producing bacteria, may lead to brain fog and other neurocognitive symptoms.

Seven patients presented with unexplained abdominal gas and brain fog treated with probiotics. The authors evaluated these patients with abdominal bloating, SIBO, and gas for metabolic acidosis. 


Only patients with normal upper endoscopy, duodenal biopsies, colonoscopy or biopsy, abdominal CT imaging, and hematological and chemical profiles were included. The authors also enrolled a group of patients with similar symptoms who did not have brain fog. All patients completed a validated questionnaire. The questionnaire measured 9 symptoms: nausea, vomiting, abdominal pain, bloating, and fullness. Scores greater than 5 were considered severe. Patients were asked not to use laxatives or drugs that affect intestinal motility (opioids and anticholinergics) for at least one week prior to the study. Within one week, patients were required to have duodenal aspirate, cultures, and a glucose breath test. During testing, no new medications were permitted. After a carbohydrate test, metabolic testing was done. This included blood glucose, insulin, ammonia levels, and levels of L-lactate, L-lactate, and urine D-lactic acid. The wireless motility capsule test (SmartPill(r)) was used to evaluate gastrointestinal transit. Subjects ingested capsules containing temperature, pressure, and temperature sensors. They also wore a recorder for five days to monitor their transit. The authors also performed a gastric emptying test using radioactive technetium meals and a colonic transit test where subjects ingested capsules with 24 radio-opaque markers.


The authors evaluated a total of 42 patients. There were 34 patients with brain fog and eight who had no brain fog. Four patients with brain fog category were exempted due to recent antibiotic use, inability or technical difficulties with sample collection/transportation, and a new diagnosis for Parkinson's disease. Thirty patients (f/m = 19/11; mean age 52 years) were included. Six patients were gluten-restricted, and three were on a low FODMAP diets. One patient was on the Paleo diet. All 8 patients with out brain fog met the inclusion criteria.

Gastrointestinal symptoms

96.77% of patients with brain fog had abdominal pain. Other symptoms were bloating (93.3%), fullness (90%), gas (90%), cramping (80%), distention (90%), fullness (90), fullness (90%), stomach ache (90%), gas (90%), cramping (80%), diarrhea (76.7%) and belching (90). The most common symptoms in the patients without brain fog were abdominal pain (75%), bloating (100%), fullness (88%), gas (100%), and belching (88%).

Brain fog

All patients with brain fog described neurocognitive symptoms such as mental confusion, impaired judgment, short-term memory problems, and difficulty with concentration. These symptoms could last from 30 minutes to several hours, sometimes after meals, and intermittently throughout the day. Brain fog was so severe, 4/30 (33.3%) quit their jobs.

Use of probiotics and other medications

All patients with brain fog were taking probiotics. 7 patients used opiates (23.3%), and 13 (43.3%) used multivitamins and PPIs. Four patients used fish oil and biotin supplementation, and 1 patient used simethicone and melatonin, saw palmetto, and artemisinin.

SIBO cultures

Cultures for SIBO were positive in 14 patients (46.7%) and negative in 14 patients (46.6%).

Metabolic testing (lactic acid)

D-lactic acidosis was observed in 23 patients (76.7%) with brain fog. Concurrent L-lactic acidosis occurred in 9 (30%) patients. Two (28%) of the patients without brain fog group had D-lactic acidosis, and one also had L-lactic acidosis. D-lactic acidosis prevalence was significantly higher in patient with brain fog compared to patients without brain fog.

Assessment of Gastrointestinal Transit

5/30 (16.7%) of 30 patients were diagnosed with gastroparesis. One patient had rapid gastric emptying, while the rest had normal small bowel and colonic transit. Six out of 24 (25%) patients with colonic transit studies found slow transit constipation. Evidence of SIBO was present in 10 dysmotility patients.

Follow up

All SIBO patients who had evidence of lactic acidosis or SIBO were treated with antibiotics. Patients with no evidence of SIBO were advised to stop using probiotics or yogurt. 70% of patients experienced significant improvement in their symptoms.


The authors describe a group of patients with brain fog associated with abdominal bloating, pain, gas, and distension. These patients had SIBO, D-lactic acidosis and used probiotics. The prevalence of both D-lactic acidosis and SIBO was significantly higher in patients with brain fogginess compared to those without brain fogginess.

Probiotics commonly contain lactobacilli which produce D-lactic acid. These D-lactate-producing bacteria colonize the colon, producing large quantities of D lactic acid, which causes rapid fermentation and gaseous distension, which can overwhelm the liver's ability to clear lactic acid. The production of toxic metabolites, such as D-lactic acids in the small intestine due to bacterial fermentation of carbohydrate substrates causes brain fog. The use of probiotics or cultured yogurt for prolonged periods and excessive amounts contributes to colonization of the small intestine by lactobacilli and other bacteria. These bacteria are resistant to most antibiotics, which further explains the refractory nature of these symptoms.

Probiotics can be beneficial and safe, but this study showed that probiotics may be associated with brain fog in certain patients. The authors speculate that probiotics may colonize small bowels in low- or dysmotility conditions, which favor bacterial growth. 

All patients with SIBO were treated with antibiotics. Probiotics were stopped. Dietary advice was given to the remaining patients. The authors found that 70% of patients with SIBO experienced significant improvements in their symptoms. 85% of patients had complete resolution of brain fog, confirming that SIBO and D-lactic acidosis were the causes of brain fogginess. Patients with brain fog had significantly more SIBO and D–lactic acidosis than patients without it. The authors caution against the excessive use of probiotics in excess without a medical reason, especially in particularly in patients with dysmotility or using proton pump inhibitors (PPIs) such as Prilosec or Nexium or opioids, for long periods of time.




Brain fogginess, gas and bloating: a link between SIBO, probiotics and metabolic acidosis

Back to blog

You might want to check

1 of 12