Insights into human colonic physiology obtained from the study of flatus composition

To better understand the physiology of colonic gas production, each flatus passage of 16 subjects over a 4-h period was analyzed by gas chromatography for N₂, O₂, H₂, CO₂, CH₄, and for odoriferous sulfur- containing gases. Appreciable intraindividual and enormous interindividual variability was observed, indicating that each gas passage reflected the interaction of highly variable liberation and/or removal mechanisms. The predominant flatus gas was CO₂, H₂, and N₂ in seven, six, and three subjects, respectively. Gases produced intraluminally (H₂, CO₂, and CH₄) comprised ~74% of flatus, and rapid CO₂ and H₂ productions were responsible for high passage rates. A positive correlation between flatus H₂ and CO₂ suggested that CO₂, like H₂, mainly was a bacterial product. Whereas methanogens and H₂S-producing bacteria usually are mutually exclusive in feces, CH₄ and H₂S did not negatively correlate, indicating coexistence of both organisms in the colon. We conclude that analysis of flatus composition provides a novel means of assessing colonic physiology, particularly ongoing bacterial metabolism throughout the unperturbed colon.