Fermentation of endogenous substrates is responsible for increased fasting breath hydrogen levels in celiac disease.

Fasting breath hydrogen (FBH) levels are frequently increased in celiac disease (CD). In this study we sought to determine whether the unknown source of the fermented substrates is endogenous glycoproteins shed or exuded through the damaged mucosa. To test the role of nonabsorbable exogenous substrates, we subjected 39 untreated and 23 treated CD patients and 37 healthy volunteers to the H(2) breath test after administration of lactulose after both an unrestricted and a restricted pretest meal. To test the relevance of endogenous substrates, we measured breath H(2) excretion during a 9-hour fast and after the administration of lactulose solution. To determine whether the luminal content of CD patients contains an increased amount of fermentable substrates, we incubated samples of jejunal juice from 7 untreated CD patients, 6 healthy volunteers, and 6 dyspeptic patients in vitro with a fecal homogenate obtained from a healthy H(2)-producer volunteer and measured the cumulative H(2) production. Untreated CD patients showed higher FBH levels than did treated patients and healthy volunteers. Only in untreated CD did FBH levels show no difference if a restricted or an unrestricted dinner was eaten the evening before the test. Nine-hour FBH levels were significantly higher in untreated CD than in healthy volunteers, whereas no difference was found after administration of lactulose. In vitro H(2) production was significantly higher in untreated CD patients than in controls. Increased FBH levels in CD do not depend on fermentation of malabsorbed exogenous substrates; endogenous substrates are increased in the lumens of CD patients and may be responsible for increased FBH levels.