What are the sources of molecular hydrogen in human breath?
Hydrogen in breath arises from normal intestinal bacteria, mainly in the colon, which break down (ferment) the undigested nutrients that have passed through the small intestine. Hydrogen is absorbed from the intestine into the blood and exhaled via the lungs.

Conditions in which intestinal bacteria produce hydrogen:


Normal digestion in which soluble dietary fiber is not digested in the small intestine. Examples of soluble fiber: beta-glucan (in oats and barley), pectin (in apples) fructo-oligosaccharides (in red onions), raffinose (in beans), etc.
Lactose intolerance in which lactose remains undigested due to lack of the enzyme lactase (gas is produced mainly after ingesting milk)
Fructose malabsorption in which fructose absorption is reduced due to lack of a certain molecule in the intestinal lining (gas is produced after eating foods high in fructose: apples, pears, honey, agave, etc.)
Sucrose intolerance due to lack of the enzyme that digests sucrose
Small intestinal bacterial overgrowth (SIBO) due to various malabsorptive conditions


Hydrogen breath test is an established method for diagnosing various intestinal disorders. It includes drinking a solution high in certain substance (lactose, fructose..., depending on which disorder is expected) and measuring hydrogen in the exhaled air.

To properly interpret the results of a hydrogen test you need to consider the time in which hydrogen appears in breath after ingestion of a certain substance.

Food Marble provides a relatively thin explanation of their breath test. The question is if this test can distinguish between the hydrogen produced during normal digestion of the soluble fiber and hydrogen produced in the mentioned intestinal disorders.

Business Insider made a review of FoodMarble in which they mention some other reviews...In summary: it's not proven reliable, yet.