From the Guidelines
Small Intestine Bacterial Overgrowth (SIBO) is a complex condition with a multifactorial etiology, involving disruption of normal protective mechanisms that prevent bacterial overgrowth, and its causes include anatomical abnormalities, motility disorders, impaired gastric acid secretion, immunodeficiency states, and other contributing factors such as pancreatic enzyme deficiency and medications that slow motility. The etiology of SIBO is typically characterized by the presence of bacteria not usually found in the small intestine, leading to excessive fermentation and inflammation, and resulting in adverse clinical symptoms such as malabsorption, abdominal discomfort, diarrhea, constipation, flatulence, and bloating 1.
Common Causes of SIBO
- Anatomical abnormalities: intestinal strictures, diverticula, fistulas, or surgical alterations like blind loops that create stagnant areas where bacteria can accumulate
- Motility disorders: conditions like gastroparesis, intestinal pseudo-obstruction, and diabetic enteropathy, which slow intestinal transit and allow bacteria to proliferate
- Impaired gastric acid secretion: proton pump inhibitor use, gastric surgery, or autoimmune conditions that remove an important antibacterial barrier
- Immunodeficiency states: IgA deficiency, common variable immunodeficiency, and AIDS, which compromise the immune system's ability to control bacterial populations
Other Contributing Factors
- Pancreatic enzyme deficiency: leaves undigested food for bacterial fermentation
- Medications: narcotics and anticholinergics that slow motility
- Conditions: celiac disease, Crohn's disease, and radiation enteritis that damage the intestinal mucosa
Understanding these underlying causes is essential for effective treatment, as addressing the root cause alongside antimicrobial therapy provides the best chance for long-term management of SIBO 1. The treatment of SIBO may require several courses of antibiotics, and it may recur; therefore, SIBO should be considered in patients with chronic pancreatitis even if they have not had prior surgery, where pancreatic enzyme replacement therapy appears to insufficiently treat gastrointestinal symptoms 1.
From the Research
Etiology of Small Intestine Bacterial Overgrowth (SIBO)
The etiology of SIBO is complex and multifactorial. Several factors can contribute to the development of SIBO, including:
- Disorders of protective antibacterial mechanisms, such as achlorhydria, pancreatic exocrine insufficiency, and immunodeficiency syndromes 2
- Anatomical abnormalities, such as small intestinal obstruction, diverticula, fistulae, surgical blind loop, and previous ileo-caecal resections 2
- Motility disorders, such as scleroderma, autonomic neuropathy in diabetes mellitus, post-radiation enteropathy, and small intestinal pseudo-obstruction 2
- Reduced intestinal motility, altered gastrointestinal anatomy, reduced gastric acid or pancreatic enzyme production, altered bile acid metabolism, or immune defects 3
- Acid-suppressive therapies, alterations in gastrointestinal motility and anatomy, as well as impoverished conditions 4
Risk Factors
Several risk factors have been identified that can predispose individuals to SIBO, including:
- Acid-suppressive therapies 4
- Alterations in gastrointestinal motility and anatomy 4
- Impoverished conditions 4
- Obesity, although the connection between SIBO and obesity remains controversial and unclear 5
- Celiac disease, irritable bowel syndrome, inflammatory bowel disease, and hepatic cirrhosis 5
Underlying Mechanisms
The underlying mechanisms of SIBO involve an excessive growth of select microorganisms within the small intestine, which disrupts host physiology and leads to gastrointestinal and non-gastrointestinal symptoms and complications 4. The connection between SIBO and the gut microbiota is complex, and diet has a fundamental influence on the composition of the intestinal microbiome 3.