What diseases are associated with Small Intestine Bacterial Overgrowth (SIBO)?

What Diseases Does SIBO Cause?

SIBO does not directly "cause" diseases but rather develops secondary to underlying conditions and then produces a malabsorption syndrome with specific nutritional deficiencies and gastrointestinal complications. 1, 2

Primary Clinical Consequences of SIBO

Malabsorption Syndrome

• Steatorrhea (fatty diarrhea) develops when bacterial overgrowth deconjugates bile salts and degrades pancreatic enzymes, preventing normal fat digestion and absorption 1, 2
• Protein-losing enteropathy can occur, with subtotal villous atrophy sometimes found on small bowel histology 1
• Osmotic diarrhea results from bacterial deconjugation of bile acids in the small intestine, with excess transmission to the colon 1, 3

Fat-Soluble Vitamin Deficiencies

• Vitamin A deficiency causes night blindness, poor color vision, dry flaky skin, and xerophthalmia 1, 3
• Vitamin E deficiency produces peripheral neuropathy, ataxia, ophthalmoplegia, and myopathy 1, 3
• Vitamin D deficiency increases fracture risk, though this is less commonly affected than vitamins A and E 1, 3
• Vitamin K deficiency is rare because bacteria can manufacture it, but when present causes easy bruising and prolonged bleeding 1, 3

Water-Soluble Vitamin and Mineral Abnormalities

• Vitamin B12 malabsorption occurs, while folic acid and vitamin K may paradoxically be elevated due to bacterial production 1
• Iron and calcium deficiencies develop from malabsorption 4

Metabolic Complications

Rare but Serious Metabolic Derangements

• D-lactic acidosis (high anion gap acidosis) can occur when bacteria manufacture D-lactic acid instead of the normal L-isomer 1
• Hyperammonemia may develop when bacteria produce excessive ammonia that appears in high blood levels 1

Severe Manifestations of Advanced Disease

Malnutrition and Its Consequences

• Weight loss exceeding 10% of body weight produces demonstrable physiological changes including skeletal and cardiac muscle weakness, poor concentration and memory, prolonged sleeping, reduced sexual function, low body temperature, and increased susceptibility to severe infections 1
• Mucosal malabsorption worsens with progressive undernutrition 1

Diseases Where SIBO Develops as a Complication

Gastrointestinal Disorders

• SIBO is present in one-third of patients with Crohn's disease, with prior surgery and fibrostenosing disease as major risk factors 1, 5
• Ulcerative colitis shows substantially increased SIBO prevalence 1, 5
• Celiac disease has bidirectional associations with SIBO 1, 5
• Irritable bowel syndrome shows significant symptom overlap with SIBO, making clinical distinction challenging without breath testing 2, 5
• Functional dyspepsia, functional abdominal bloating, functional constipation, and functional diarrhea are significantly associated with SIBO 5
• Short bowel syndrome and chronic intestinal pseudo-obstruction predispose to SIBO 5
• Diverticular disease increases SIBO risk 5

Hepatobiliary and Pancreatic Diseases

• Cirrhosis shows correlation between disease severity and SIBO presence 5
• Metabolic-associated fatty liver disease (MAFLD) demonstrates associations with SIBO 5
• Primary biliary cholangitis is linked to SIBO development 5
• Chronic pancreatitis with exocrine insufficiency shows SIBO in up to 92% of patients due to reduced bacteriostatic pancreatic secretions 6, 5
• Cystic fibrosis predisposes to SIBO 5

Endocrine and Metabolic Disorders

• Diabetes mellitus with autonomic neuropathy causes intestinal dysmotility, slowing orocecal transit and allowing bacterial proliferation 6, 5
• Hypothyroidism decreases motor-stimulating thyroid hormone influence on intestinal transit 5
• Hyperlipidemia is associated with SIBO 5
• Acromegaly shows increased SIBO prevalence 5

Neurological and Rheumatological Conditions

• Multiple sclerosis, Parkinson's disease, and autism spectrum disorder are associated with SIBO 5, 4
• Systemic sclerosis (scleroderma) causes intestinal dysmotility predisposing to SIBO 5, 4
• Spondylarthropathy and fibromyalgia show associations with SIBO 5

Other Systemic Conditions

• Heart failure is linked to SIBO development 5
• Asthma shows associations with SIBO 5
• Obesity may have higher SIBO prevalence 4

Key Pathophysiologic Mechanisms

How SIBO Produces Its Effects

• Impaired migrating myoelectric complex (MMC) prevents clearance of intestinal debris, creating gut stasis that allows anaerobic bacteria to proliferate in stagnant bowel loops 1, 2, 6
• Bacterial fermentation of unabsorbed carbohydrates produces hydrogen and methane gas, causing bloating and flatulence 2
• Reduced gastric acid secretion (often from proton pump inhibitors) eliminates the normal acid barrier against bacterial overgrowth 6, 5
• Incompetent ileocecal valve allows colonic bacteria to reflux backward into the small intestine 6

Important Clinical Distinctions

• SIBO is not contagious and cannot be transmitted person-to-person, as it develops from overgrowth of bacteria already present in the gastrointestinal tract 6
• Normal inflammatory markers (fecal calprotectin) are expected in SIBO; elevated levels should prompt investigation for inflammatory bowel disease instead 2
• SIBO often develops secondary to underlying diseases rather than being a primary pathogen 7, 8