How Does the Breath Test Work?
Common dietary sugars such as lactose and fructose are normally absorbed in the small intestine. However, some people do not completely absorb these sugars and they pass into the colon (large intestine) where they are fermented by bacteria to produce either hydrogen (H2) or methane (CH4) gas, or a combination of both.
In FODMAP intolerance an orally-ingested test sugar will be incompletely absorbed in the small intestine, leading to fermentation and gas production in the colon. These gases are absorbed into the bloodstream and expired via the lungs, allowing detection by breath testing. As these gases are not produced by humans, they are evidence of sugar fermentation by intestinal bacteria and hence breath tests are highly specific.
FODMAP Intolerance and SIBO are indicated by a significant rise in breath hydrogen or methane levels above baseline during the test.
As a quantitative test it can also provide some information on the degree of intolerance.