Small intestinal bacterial overgrowth

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Small intestinal bacterial overgrowth (SIBO) is an excessive bacterial growth in the small intestine which in contrast to the large intestine in healthy individuals contains relatively small populations of bacteria.

Prevalence[edit | edit source]

The rate of a positive lactulose test is low in healthy adults (0 to 20%).[1]

Comorbidities[edit | edit source]

Anecdotal reports suggest a high prevalence of SIBO among CFS patients. One study found 77% of CFS patients had SIBO and eradication lead to decrease in symptoms.[2] Several studies have shown that up to 84% of patients with irritable bowel syndrome have SIBO[1] and that symptoms improve after treatment[3][4], while others fail to replicate these results[5][6].

One study found that a 100% of fibromyalgia patients tested positive to a lactulose breath test, indicating SIBO, and that the degree of abnormality on the breath test correlated with the amount of pain reported.[3] Patients with CFS have alterations in microbiota, including lower levels of bifidobacteria and SIBO[7]

Risk factors[edit | edit source]

Risk factors include bowel resection, bariatric surgery, disordered motility, disorders of the immune system such as IgA deficiency, low stomach acid, the use of proton pump inhibitors and immunosuppressants, and recurrent antibiotic use.[1] Hypothyroidism and T4-only thyroid hormone replacement are both strongly associated with SIBO. (Please format these citations:,

Conditions that affect gut motility such as gastroparesis and celiac disease increase the risk of SIBO.[1] Rates of SIBO are also higher in Crohn's disease, pancreatitis, and renal failure.[1]

SIBO is more common among the elderly.[1]

Diagnosis[edit | edit source]

SIBO can be diagnosed using a hydrogen breath test. The diagnosis of SIBO is controversial due to the species-dependent nature of breath tests and the lack of an agreed threshold for a positive test.[1] It can also be diagnosed through bacterial culture, but this is rare as it requires intubation of the small intestine.

Pathophysiology[edit | edit source]

Bacteria commonly implicated in SIBO include Escherichia coli, Streptococcus, Lactobacillus, Bacteroides and Enterococcus.[8] Higher levels of Enterococcus and Stretptococcus have been found in ME/CFS patients.[9]

Health complications[edit | edit source]

The symptoms of SIBO can vary greatly depending on the severity and the species of bacterial populating the small intestine.[6] Symptoms include bloating, abdominal distension, abdominal pain or discomfort, diarrhea, fatigue, and weakness.

It causes increased permeability of the small intestine.[10] It can cause malabsorption of nutrients including iron and Vitamin B12, resulting in microcytic anemia or megaloblastic anemia.

Nutritional deficiencies[edit | edit source]

Vitamin B12 malabsorption may be caused by competitive uptake of B12 by bacteria in the small intestine.[1] It can also cause excess folic acid due to synthesis by bacteria in the small bowel.[11]

In severe cases, malabsorption of fat-soluble vitamins (A,D,E and K) due to the deconjugation of bile salts can cause neuropathies and immune dysfunction.

SIBO can also cause carbohydrate and protein malabsorption.[1]

Treatment[edit | edit source]

Standard treatment is a course of antibiotics. [12] The best evidence for patients without constipation is for the use of rifaximin, an antibiotic that is stays in the intestine and is not absorbed in the body.[13] Some SIBO researchers recommend adding Neomycin to rifaxamin for patients with constipation, as neomycin appears to help kill methane-producing bacteria. [14] However, one study comparing two herbal formulations to standard treatment found herbs to be as or more effect as antibiotics for eradicating SIBO.[15]

Experts also recommend the use of prokinetic drugs or herbs for those for whom dysmotility is an issue.[1]

Probiotics may also be helpful. Lactobacillus casei has been found to improve breath hydrogen scores after six weeks of treatment.[16] There is also evidence for VSL #3 in the treatment of SIBO.[17] However, some probiotics may exacerbate SIBO, in particular those containing D-Lactate producing strains.

See also[edit | edit source]

References[edit | edit source]

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Dukowicz, AC; Lacy, BE; Levine, GM (Feb 2007), "Small Intestinal Bacterial Overgrowth", Gastroenterology & Hepatology, 3 (2): 112–122, PMID 21960820 
  2. Pimentel, M; Hallegua, D; Chow, EJ; et al. (1 Apr 2000), "Eradication of small intestinal bacterial overgrowth decreases symptoms in chronic fatigue syndrome: A double blind, randomized study", Gastroenterology, 118 (4): –414, doi:10.1016/S0016-5085(00)83765-8 
  3. 3.0 3.1 Pimentel, M; Wallace, D; Hallegua, D; et al. (Apr 2004), "A link between irritable bowel syndrome and fibromyalgia may be related to findings on lactulose breath testing", Annals of the Rheumatic Diseases, 63 (4): 450–452, doi:10.1136/ard.2003.011502, PMID 15020342 
  4. Lin, HC (18 Aug 2004), "Small intestinal bacterial overgrowth: A framework for understanding irritable bowel syndrome", JAMA, 292 (7): 852–858, doi:10.1001/jama.292.7.852 
  5. Walters, B; Vanner, SJ (Jul 2005), "Detection of bacterial overgrowth in IBS using the lactulose H2 breath test: comparison with 14C-D-xylose and healthy controls", The American Journal of Gastroenterology, 100 (7): 1566–1570, doi:10.1111/j.1572-0241.2005.40795.x, PMID 15984983 
  6. 6.0 6.1 Parisi, Giancarlo; Leandro, Gioacchino; Bottona, E; et al. (Nov 2003), "Small intestinal bacterial overgrowth and irritable bowel syndrome", The American Journal of Gastroenterology, 98 (11): 2572–2573–2574, doi:10.1111/j.1572-0241.2003.08686.x, PMID 14638371 
  7. Logan, Alan C; Venket Rao, A; Irani, Dinaz (Jun 2003), "Chronic fatigue syndrome: lactic acid bacteria may be of therapeutic value", Medical Hypotheses, 60 (6): 915–923, PMID 12699726 
  8. Bouhnik, Yoram; Alain, Sophie; Attar, Alain; et al. (May 1999), "Bacterial populations contaminating the upper gut in patients with small intestinal bacterial overgrowth syndrome", The American Journal of Gastroenterology, 94 (5): 1327–1331, doi:10.1111/j.1572-0241.1999.01016.x 
  9. Sheedy, John R; Wettenhall, Richard EH; Scanlon, Denis; et al. (Jul 2009), "Increased d-lactic Acid intestinal bacteria in patients with chronic fatigue syndrome", In Vivo, 2009 Jul-Aug;23(4): 621-8, PMID 19567398 
  10. Reference needed
  11. Camilo, E; Zimmerman, J; Mason, JB; et al. (Apr 1996), "Folate synthesized by bacteria in the human upper small intestine is assimilated by the host", Gastroenterology, 110 (4): 991–998, PMID 8613033 
  12. Reference needed
  13. Bures, Jan; Cyrany, Jiri; Kohoutova, Darina; et al. (28 Jun 2010), "Small intestinal bacterial overgrowth syndrome", World Journal of Gastroenterology : WJG, 16 (24): 2978–2990, doi:10.3748/wjg.v16.i24.2978, PMID 20572300 
  14. Reference needed
  15. Chedid, Victor; Dhalla, Sameer; Clarke, John O; et al. (May 2014), "Herbal Therapy Is Equivalent to Rifaximin for the Treatment of Small Intestinal Bacterial Overgrowth", Global Advances in Health and Medicine, 3 (3): 16–24, doi:10.7453/gahmj.2014.019, PMID 24891990 
  16. Barrett, Jacqueline S; Canale, Kim EK; Gearry, Richard B; et al. (2008-08-28), "Probiotic effects on intestinal fermentation patterns in patients with irritable bowel syndrome", World Journal of Gastroenterology : WJG, 14 (32): 5020–5024, doi:10.3748/wjg.14.5020, PMID 18763284 
  17. Meier, Rémy; Burri, Emanuel; Steuerwald, Michael (Sep 2003), "The role of nutrition in diarrhoea syndromes", Current Opinion in Clinical Nutrition and Metabolic Care, 6 (5): 563–567, doi:10.1097/01.mco.0000087972.83880.d3, PMID 12913674 

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From MEpedia, a crowd-sourced encyclopedia of ME and CFS science and history