Small intestinal bacterial overgrowth (SIBO) is a condition where the small intestine has too much bacteria. Normally the small intestine has < 1000 organisms/mL with mostly gram-positive organisms. The colon has WAY more bacteria than the small intestine, that are mostly anaerobic and gram-negative. SIBO can occur if there is decreased acid secretion in the stomach (such as in autoimmune/atrophic gastritis), delayed transit in the small intestine (can be seen in diabetes, scleroderma, Crohn’s disease, etc.) or other conditions that lead to stasis (small intestinal diverticulosis, altered small bowel anatomy, or strictures). Picture a pond. The water is still and stagnant with a film of algae overlying the surface. Similarly, the bacteria can multiply in a small intestine that is slow moving or doesn’t have the normal defense mechanisms. Conditions associated with SIBO include cirrhosis, renal failure, chronic pancreatitis, alcoholism, and immunodeficiency states.
Malabsorption of carbohydrates occurs due to early breakdown of sugars and reduced enzyme activity at the villi. The excessive bacteria in your small intestine also feast on unabsorbed carbohydrates leading to gas, bloating and at times diarrhea. SIBO also causes fat and protein malabsorption. Excessive bacteria not only damage the cells that line the lumen, but also cause deconjugation of bile acids which contributes to fat malabsorption. This weak barrier also has trouble absorbing amino acids from protein. SIBO can be associated with cobalamin (B12), thiamine (B1) and nicotinamide (B3) deficiency. Alternatively, rises in folate and vitamin K may be seen due to bacterial synthesis.
This condition is diagnosed with a breath test. You generally have to fast for 12 hours prior to the test. A load of glucose 75 gm or lactulose 10 gm is given and the methane and hydrogen in your breath are measured every 15 to 30 minutes for 2-4 hours. An early peak is seen in patients with SIBO due to metabolization of the substrate by bacteria in the small intestine before reaching the colon, where a peak in gas production is expected. The test is positive if there is an increase in Hydrogen ≥ 20 ppm above baseline within 1.5 hours or a methane level ≥ 10 ppm above baseline. However, labs may have different criteria in their definition of abnormal vs normal results. Read the guidelines on preparing for the exam. Antibiotics generally need to be avoided for 4 weeks. Any agent, such as a laxative, that expedites transit into the colon needs to be held for 1 week prior to the exam, as this could lead to a false positive result. Exercise and smoking need to be avoided on the day of the test.
Treatment: The goal of treatment is to reduce (not eliminate) the bacteria in the small intestine. Rifaximin is the go-to drug for predominantly Hydrogen gas producers. It is well tolerated but can be ridiculously expensive! Check with your insurance to see if it will be covered. Methane producers may need the addition of Neomycin to the above Rifaximin regimen. 40% may not respond to treatment and recurrence can occur in forty percent. Attempts should be made to reverse the underlying process when able. Drugs such as opiates, benzodiazepines and proton pump inhibitors may contribute to the condition but talk to your physician before making any changes on your own. Pro-kinetic agents may be helpful when there is decreased motility of the upper GI tract. The role of probiotics is unclear.
Diet: Often eliminating sugars alone can help with symptoms. Adhering to a diet low in FODMAPs (fermentable Oligo-, Di-, Mono-saccharides and Polyols), which are carbohydrates that are not well absorbed in the small intestine, may or may not help. Point of clarification, foods with FODMAPs do not generally cause inflammation but can cause symptoms in SOME people. The Monash University app is helpful in learning more about this diet. Talk t o your gastroenterologist before adopting this diet, which can be restrictive.
Conclusion: If you feel like there is a balloon inflating inside of you…get it checked out! If gas is taking over your life, it doesn’t have to. It’s time to stop hiding in the corner!
References:
Pimentel, M. (2018). Small intestinal bacterial overgrowth: Management. In S Grover (ed.), UpToDate. Retrieved February 24, 2019 from
https://www.uptodate.com/contents/small-intestinal-bacterial-overgrowth-management
Pimentel, M. (2018). Small intestinal bacterial overgrowth: Clinical manifestations and diagnosis. In S Grover (ed.), UpToDate. Retrieved February 24, 2019 from
Oxentenko, A. S. (2015). Clinical Features of Malabsorptive Disorders, Small-Bowel Diseases, and Bacterial Overgrowth Syndromes. In Hauser, S.C. (Ed), Mayo Clinic Gastroenterology and Hepatology Board Review (pp 89-101). New York, NY: Oxford University Press.
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