Hydrogen and methane production by human subjects consuming various diets with and without dietary fiber

Production of breath hydrogen and methane was related to colonic degradation of fiber to determine whether breath gases were good indicators of colonic fiber breakdown. End-alveolar breath hydrogen and methane were measured in five male subjects consuming three diets: their self-selected diet (SS), a fiber-free diet (FF), and the same fiber free diet plus 75 grams of coarse white wheat bran (B). On each diet, end-alveolar breath samples were collected hourly from 0800 to 2200 hours for hydrogen analysis. Hydrogen production after ingestion of a 15 gram dose of lactulose (L) was also determined. Methane production was determined twice during each diet. Neutral detergent fiber (NDF) of the bran and the fecal composites from the bran diet were measured. Average peak hydrogen production was 64 PPM (range 39–113) during the self-selected (SS) diet and 35 PPM (range 14–59) during the liquid fiber-free diet (FF). Bran ingestion caused hydrogen production to increase to an average peak value of 44 PPM (range 25–74). Lactulose ingestion generally resulted in more hydrogen production, with an average peak of 76 PPM (range 30–142). NDF was calculated to be about 40% digestible (range 27% to 48%) during bran ingestion. These results suggest that less hydrogen is produced on a fiber-free liquid diet than on diets known to contain undigestible carbohydrates. A hydrogen breath test may be used as an indirect measure of fiber digestibility since lactulose, which is highly fermentable, produced a little less than twice the peak hydrogen response than did bran whose digestibility was calculated to be roughly 40%.