What does breath testing have to do with digestive problems?
The Breath Hydrogen Test measures the amount of hydrogen in the exhaled air. This measurement can be used to diagnose several conditions that cause gastrointestinal symptoms such as abdominal pain, bloating, distention, flatulence and diarrhea.
In people, only bacteria - especially anaerobic bacteria in the large intestine (or colon) - are capable of producing hydrogen. When bacteria in the colon is exposed to unabsorbed food, particularly sugars and carbohydrates, the bacteria produce hydrogen. Some of this hydrogen gas is absorbed through the colon into the blood stream. Then, as the blood stream passes by the lungs, the hydrogen gas in the blood is exchanged/eliminated in the lungs and is expelled in the breath where it can be measured. This measurement can be used to diagnose several conditions: abnormal digestion of dietary sugars; rapid transit (or passage) of food through the small intestine, or; small intestinal bacterial overgrowth, also known as SIBO.
Poor absorption of dietary sugars
As already mentioned, when bacteria in the colon is exposed to unabsorbed food, especially sugars and carbohydrates, the bacteria produce hydrogen. Normally, small amounts of unabsorbed food may reach your large intestine and produce a limited amount of hydrogen. As long as only small amounts of sugars and carbohydrates reach the colon, the small amount of hydrogen that is produced does not cause a problem. However, if you are having a problem with the digestion or absorption of food in the small intestine, large amounts of unabsorbed food may reach the colon and produce large amounts of hydrogen causing gastrointestinal symptoms.
When testing for poor absorption of sugars, the most common sugars that are used for testing are lactose (the sugar in milk), fructose and glucose.
Rapid transit of food through the small intestine
In addition to diagnosing poor absorption of sugars, the Breath Hydrogen Test can be used to diagnose the abnormally rapid passage of food through the small intestine. If individuals have abnormally rapid passage of food through the small intestine, there may not be enough time for their small intestine to properly absorb the food. This results in larger-than-normal amounts of undigested sugars and carbohydrates entering the colon, where the bacteria then go to work and produce larger-than-normal amounts of hydrogen.
When testing for rapid transit through the small intestine, the most common sugar used for testing is lactulose. This sugar is not digested or absorbed by people. So, in cases of rapid transit, the sugar passes very quickly through the small intestine, into the colon and hydrogen appears in breath samples quickly after ingestion.
Bacterial overgrowth in the small intestine
Another condition that the Breath Hydrogen Test may be used to diagnose is small intestinal bacterial overgrowth or SIBO - a condition in which excessive amounts of bacteria in the large intestine move back into the small intestine. When unabsorbed food that has not had a chance to complete its travel through the small intestine then encounters the colonic bacteria, excessive hydrogen is produced.
When testing for SIBO, the most common sugar used for testing is, again, lactulose. Because this kind of sugar is not digested or absorbed by people, in cases of SIBO, high levels of hydrogen will actually appear twice during the test; once as sugar encounters colonic bacteria in the small intestine and again when it encounters bacteria in the colon.
Reference: Marks, M.D., J. Hydrogen Breath Test. Retrieved from https://www.medicinenet.com/hydrogen_breath_test/article.htm#what_is_the_hydrogen_breath_test