The hydrogen breath test is a test that uses the measurement of hydrogen in the breath to diagnose several conditions that cause gastrointestinal symptoms. In humans, only bacteria - specifically, anaerobic bacteria in the colon - are capable of producing hydrogen.
The bacteria produce hydrogen when they are exposed to unabsorbed food, particularly sugars and carbohydrates, not proteins or fats. Although limited hydrogen is produced from the small amounts of unabsorbed food that normally reach the colon, large amounts of hydrogen may be produced when there is a problem with the digestion or absorption of food in the small intestine, that allows more unabsorbed food to reach the colon.
The small bowel, also known as the small intestine, is the part of the gastrointestinal tract that connects the stomach with the colon. The main purpose of the small intestine is to digest and absorb food into the body. The small intestine is approximately 21 feet in length and begins at the duodenum (into which food from the stomach empties), followed by the jejunum, and then the ileum (which empties the food that has not been digested and absorbed in the small intestine into the large intestine or colon).
The entire gastrointestinal tract, including the small intestine, normally contains bacteria. The number of bacteria is greatest in the colon (at least 1,000,000,000 bacteria per milliliter (ml) of fluid) and much lower in the small intestine (less than 10,000 bacteria per ml of fluid). Moreover, the types of bacteria within the small intestine are different than the types of bacteria within the colon. Small intestinal bacterial overgrowth (SIBO) refers to a condition in which abnormally large numbers of bacteria (at least 100,000 bacteria per ml of fluid) are present in the small intestine and the types of bacteria in the small intestine resemble more the bacteria of the colon than the small intestine.
Small intestinal bacterial overgrowth (SIBO) is also known as small bowel bacterial overgrowth