From the Guidelines
SIBO is a condition characterized by an increased bacterial load in the small bowel, resulting in excessive fermentation and inflammation, and leading to adverse clinical symptoms, including malabsorption, abdominal discomfort, diarrhea, constipation, flatulence, and bloating. This condition occurs when bacteria that normally live in other parts of the gut start growing in the small intestine, or when the normal small intestinal bacteria grow excessively 1. Common symptoms of SIBO include bloating, gas, abdominal pain, diarrhea, constipation, and sometimes weight loss or nutritional deficiencies.
Causes and Risk Factors
SIBO may complicate chronic pancreatitis in up to 92% of patients with pancreatic exocrine insufficiency (PEI) 1. It occurs more frequently in those with prior surgical history and heavy smokers. The condition is also associated with microbial imbalance (dysbiosis) in the large bowel, which may lead to the activation of inflammatory cytokines in several inflammatory-mediated diseases 1.
Treatment and Management
SIBO is typically treated with antibiotics such as rifaximin (Xifaxan) 550mg three times daily for 14 days, or alternatives like metronidazole, neomycin, or ciprofloxacin depending on the type of bacterial overgrowth 1. Dietary modifications often help manage symptoms, including a low-FODMAP diet that reduces fermentable carbohydrates. Prokinetic medications like low-dose erythromycin (50-100mg) at bedtime may help prevent recurrence by improving intestinal motility.
Key Considerations
Recurrence is common, so addressing underlying causes is essential for long-term management. The risk of resistant organisms, including Clostridioides difficile, should also be considered when using antibiotics to treat SIBO 1. Bacterial overgrowth is virtually inevitable and can cause cachexia without necessarily causing diarrhea, so antibiotics may be needed even in the absence of diarrhea 1.
Underlying Mechanisms
SIBO develops when normal protective mechanisms fail, such as decreased stomach acid, structural abnormalities, or motility disorders that allow bacteria to accumulate rather than being swept through the digestive tract. The condition is associated with decreased levels of health-enhancing gut bacteria, such as Bifidobacteria and Lactobacilli, which are believed to relieve diarrhea and malabsorption, produce short-chain fatty acids, and reduce luminal pH 1.
From the Research
Definition of Small Intestine Bacterial Overgrowth (SIBO)
- SIBO is a condition defined by the excess bacteria or changes in bacterial composition of the small intestine 2.
- It is characterized by an abnormal increase in bacterial population in the small intestine, leading to symptoms such as bloating, abdominal pain, distension, diarrhea, and eventually malabsorption 3.
- SIBO can be caused by various mechanisms such as reduced intestinal motility, altered gastrointestinal anatomy, reduced gastric acid or pancreatic enzyme production, altered bile acid metabolism, or immune defects 4.
Symptoms of SIBO
- Gastrointestinal symptoms such as bloating, abdominal distension, diarrhea, nutrient deficiencies, and even frank weight loss 2.
- Non-gastrointestinal symptoms and complications can also occur, including stunting in children 5.
- Common symptoms in children include chronic abdominal pain, abdominal distention, diarrhoea, and flatulence 5.
Diagnosis of SIBO
- Small bowel jejunal aspirate of >10^5 CFU/ml has traditionally been considered the gold standard for diagnosis 2.
- Breath tests using glucose and lactulose are commonly used non-invasive diagnostic tools, although they are subject to limitations such as false positives and false negatives 3.
- Other diagnostic methods include direct aspiration techniques and urine-based testing 2, 3.
Treatment of SIBO
- Treatment focuses on the eradication of excess bacteria in the small bowel and is traditionally done with the use of oral antibiotics 2.
- Rifaximin is effective in most cases of SIBO, while systemic antibiotics like metronidazole and ciprofloxacin are alternatives 3.
- Probiotics, diet manipulation, and prokinetic agents are emerging therapies that may also be effective in treating SIBO 2, 6, 4.
- Elemental diets, carbohydrate-reduced diets, and pre- and probiotics are potential therapy options 4.