SIBO Breath Testing: How It Works, Preparation and Results
- Jul 28
- 5 min read
What is SIBO and why do we test for it?
Persistent digestive symptoms such as bloating, excessive gas, abdominal pain, constipation, diarrhoea and increasing food intolerances are often attributed to IBS. However, for some people, they may be associated with excessive microbial fermentation in the upper digestive tract, this is known as SIBO (small intestinal bacterial overgrowth).
SIBO was once treated as one condition with one standard protocol. We now recognise several distinct patterns:
Hydrogen-dominant SIBO, involving excessive bacterial fermentation in the small intestine
Intestinal methanogen overgrowth (IMO), involving methane-producing archaea in the small intestine
Intestinal sulfide overproduction (ISO), an emerging term describing excessive hydrogen sulfide production
Combined patterns, in which more than one gas is elevated suggesting many different species have taken over the upper digestive tract.
These distinctions matter because the microorganisms produce different gases, are associated with different bowel patterns, and may require different treatment approaches. Methane is strongly associated with slower transit and constipation, while hydrogen and hydrogen sulfide patterns are more commonly associated with diarrhoea and urgency. However, symptoms alone cannot reliably identify the organisms present.
A breath test provides more useful information than symptoms alone, allowing treatment to be targeted rather than relying on a generic SIBO protocol that mostly results in relapse (up to 44% of patients relapse in the first 9 months with generic treatment that only targets the infection and doesn't prioritse the landscape that enabled the infection). Due to this, in some cases, I also recommend comprehensive microbiome testing to assess the broader intestinal environment.
How does a SIBO breath test work?
A SIBO breath test is a simple, non-invasive test that can usually be completed at home. After following the preparation instructional guide that I give you, you drink a measured sugar solution and collect breath samples every 20 minutes over approximately three hours.
When intestinal microorganisms ferment the solution, they produce gases that enter the bloodstream, travel to the lungs and are released in the breath. Measuring how these gases change over time provides information about where fermentation may be occurring and which species-type may be dominant.
Results must be interpreted alongside your symptoms, bowel habits, health history and possible underlying drivers. They should not be viewed as an isolated positive or negative number.
What do the different gases mean?
Hydrogen
Hydrogen is produced when bacteria ferment carbohydrates. A rise of at least 20 parts per million above baseline within the first 90 minutes is commonly used as one criterion for hydrogen-dominant SIBO. It is frequently associated with bloating, gas, abdominal discomfort and diarrhoea, although symptoms vary.
Methane
Methane is produced by archaea rather than bacteria. A level of 10 parts per million or higher at any point during the test, including at baseline, is commonly considered evidence of intestinal methanogen overgrowth. Methane is associated with slower intestinal transit, and higher levels tend to correlate with more severe constipation. Because methanogens may be present in either the small or large intestine, the correct term is intestinal methanogen overgrowth (IMO rather than methane-dominant SIBO.
Hydrogen sulfide
Hydrogen sulfide is produced by several groups of gut bacteria, including sulfate-reducing bacteria. Excessive production has been associated with diarrhoea, urgency, bloating and abdominal pain and may occur alone or alongside SIBO or IMO. Direct hydrogen sulfide breath testing is not currently available in Australia. Symptoms, bowel patterns and hydrogen and methane results may raise clinical suspicion of what is now know as Intestinal Sulfide Overproduction (ISO), but they cannot confirm it directly.
Combined patterns
More than one gas pattern may be present. Hydrogen-producing bacteria and methane-producing archaea often coexist because methane archaea use hydrogen to produce methane. Combined patterns may produce mixed or fluctuating symptoms and can influence treatment.
Why is SIBO breath-test preparation so important?
Correct preparation is critical for an interpretable result. The purpose of the prep diet is to reduce background fermentation so that changes following the test solution can be measured accurately. Even small deviations from the prep diet can elevate baseline gases, create an apparent false-positive result, hide the true response or make the test difficult to interpret.
Preparation generally includes a temporary low-fermentation diet, an overnight fast and avoiding smoking, vigorous exercise, eating and sleeping during the collection period. Some medications and supplements may also need to be withheld where clinically appropriate. I provide you with a thorough Guide anc consultation on completing the test. If preparation cannot be completed correctly, it is usually better to postpone the test than risk receiving an unreliable result.
Can a stool test detect SIBO?
A standard stool test primarily examines microorganisms and markers from the large intestine. It cannot reliably determine whether excessive fermentation is occurring in the small intestine. Therefore, a negative Medicare-funded PCR stool test from the GP does not exclude SIBO or IMO.
Comprehensive microbiome testing organised through Microba can provide useful information about the wider bowel environment, including microbial balance, digestive function, inflammation and potential pathogens. However, it answers a different question from a breath test. In some cases, I use both to assess the gas pattern alongside the broader gut environment. If both tests are being completed, I generally recommend collecting the microbiome sample before starting the SIBO preparation diet.
What can a SIBO breath test tell us?
Breath testing may identify:
An early rise in hydrogen consistent with hydrogen-dominant SIBO
Methane levels consistent with intestinal methanogen overgrowth
Combined hydrogen and methane species overgrowth
Relationships between gas production and symptoms during testing
This can help explain different bowel patterns and why a previous generic treatment may not have produced lasting improvement.
What can’t a SIBO breath test tell us?
Breath testing cannot identify every microbial species, diagnose every cause of digestive symptoms or explain why an overgrowth developed. Results can also be influenced by preparation, intestinal transit, the chosen test solution and the gases measured. A negative result does not mean that symptoms are imagined or that no digestive problem exists. It means the test did not identify the gas pattern being assessed under those testing conditions.
Why does interpretation matter?
A breath-test report should not be interpreted using one number alone. I consider:
Baseline gas levels
When and how each gas rises
Interactions between hydrogen and methane
Symptoms experienced during testing
Usual bowel patterns and health history
Possible underlying drivers
Factors affecting preparation or intestinal transit
This is particularly important when results sit close to a diagnostic threshold, show elevated baseline gases, or do not fit neatly into a positive or negative category.
What happens after testing?
The purpose of testing is to identify the microbial pattern most likely to be contributing to symptoms and use that information to develop a targeted treatment plan.
Treatment may include an initial antimicrobial phase, followed by support for digestion, intestinal motility, the intestinal lining and the broader microbiome. It is also important to investigate why the overgrowth developed. Possible drivers include food poisoning or illness, surgery or anaesthesia, endometriosis, adhesions, structural changes, reduced stomach acid, medication effects and impaired ileocecal valve function.
Without addressing these factors, symptoms may improve temporarily and later return. This is why I use a phased approach involving antimicrobial treatment, repair and restoration, followed by maintenance and relapse prevention.
Is SIBO breath testing right for you?
Breath testing may be worth considering when persistent bloating, excessive gas, abdominal pain, constipation, diarrhoea, reflux or food reactions remain unexplained or have repeatedly been attributed to IBS. Or, when "nothing helps".
Testing is not necessary for everyone. The decision should be based on your symptoms, medical history, previous investigations and whether the result is likely to meaningfully change treatment. We will investigate this in depth in our appointment.
