SIBO Breath Testing: What It Is and How It Works

Small intestinal bacterial overgrowth (SIBO) is a condition where there is an overgrowth of bacteria in the small intestine, which can lead to a range of digestive symptoms such as bloating, abdominal pain, and diarrhoea or constipation. SIBO breath testing is a non-invasive way to diagnose SIBO, by measuring the gases produced by the bacteria in the small intestine.


How does SIBO breath testing work?

SIBO breath testing involves drinking a solution of lactulose or glucose, which are sugars that are not absorbed by the body and pass through to the small intestine. As the bacteria in the small intestine consume these sugars, they produce gases such as hydrogen and methane, which are then exhaled in the breath.

The levels of these gases are measured at regular intervals over a period of three hours. The rise in gas in the first 90 minutes of the test assesses whether there is any bacterial overgrowth in the small intestines. The test is performed after an overnight fast and after a 1-day prep diet with zero fibre consumed. During the test, the individual will be asked to breathe into a specially-designed test tube every 20 minutes.

The test is non-invasive and generally well-tolerated. It’s important to breathe into the tube with a normal exhale rather than blowing excessively into the tube. Excess carbon dioxide in the breath will invalidate the results if too much air is blown into the tube.


Check out this YouTube video which demonstrates how to correctly carry out a SIBO breath test: A SIBO breath test can be done at home and the test kit is shipped back to the lab for analysis. The test tubes are specially designed to prevent gas from escaping. SIBO breath tests typically cost £150-170.  



Interpreting SIBO test results


The results of the SIBO breath test are usually available within a few days depending on which lab is used. A positive test for SIBO is indicated by a significant rise in the levels of hydrogen and/or methane gas during the first 90-minutes of the test.

The test results can also indicate the location of the bacterial overgrowth – hydrogen-dominant SIBO suggests an overgrowth in the upper small intestine, while methane-dominant SIBO suggests an overgrowth in the lower small intestine.

  • A rise of more than 20ppm in hydrogen indicates a positive hydrogen-dominant SIBO test result
  • A rise of more than 12ppm in methane indicates a positive methane-dominant SIBO test result
  • A combined rise of more than 15ppm for both hydrogen and methane indicates a positive mixed SIBO test result
  • In cases of severe constipation, a rise of only 3ppm in methane indicates a positive methane-dominant SIBO test result
  • If either hydrogen or methane gas is elevated from baseline (before the lactulose solution is ingested) large intestinal bacterial overgrowth is indicated.


Treatment options for SIBO

If SIBO is diagnosed, treatment options include antibiotics such as Rifaximin and metronidazole, herbal antimicrobials such as oregano, berberine and allicin, and dietary changes. Antibiotics are often prescribed to kill off the overgrowth of bacteria, but they may not be effective in all cases and can have side effects. Herbal antimicrobials are an alternative treatment option that may be just as effective as antibiotics but with fewer side effects and a lower relapse rate.

Check out this website which provides information on the effectiveness of antibiotics and herbal treatment. Dietary changes can also be effective in managing SIBO symptoms.

A low FODMAP diet, which restricts fermentable carbohydrates that can exacerbate bacterial fermentation in the gut, can be helpful in reducing symptoms of bloating, abdominal pain, and diarrhoea or constipation. Other dietary changes may include avoiding certain foods that trigger symptoms, such as dairy or gluten, and eating an anti-inflammatory diet that supports gut health, including probiotics and prebiotics.


In conclusion, SIBO breath testing is a useful tool in diagnosing SIBO and can help guide treatment options. However, it’s important to interpret the test results in the context of a person’s symptoms and medical history. Treatment options include antibiotics, herbal antimicrobials, and dietary changes, with a low FODMAP diet being a particularly effective dietary approach to managing SIBO symptoms. Get in touch if you’re interested in testing for SIBO! 


Chedid V, Dhalla S, Clarke JO, et al. Herbal therapy is equivalent to rifaximin for the treatment of small intestinal bacterial overgrowth. Glob Adv Health Med. 2014 May;3(3):16-24. doi: 10.7453/gahmj.2014.019. PMID: 24891990; PMCID: PMC4030608.


Khoshini, R., Dai, S., Lezcano, S., Pimentel, M. (2008). A systematic review of diagnostic tests for small intestinal bacterial overgrowth. Digestive Diseases and Sciences, 53(6), 1443-1454. doi: 10.1007/s10620-007-0065-1


Pimentel, M., Chow, E. J., & Lin, H. C. (2003). Eradication of small intestinal bacterial overgrowth reduces symptoms of irritable bowel syndrome. The American Journal of Gastroenterology, 98(8), 1635-1640. doi: 10.1111/j.1572-0241.2003.07530.x


Sorathia SJ, Chippa V, Rivas JM. Small Intestinal Bacterial Overgrowth. [Updated 2023 Apr 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: