The role of methane in intestinal diseases.

The volume of human intestinal gas is about 200 ml, and it is derived from complex physiological processes including swallowed air, diffusion from bloodstream into the lumen, and particularly intraluminal production by chemical reactions and bacterial fermentation. Gas is continuously removed by eructation, anal evacuation, absorption through the intestinal mucosa, and bacterial consumption. More than 99% of it is composed of hydrogen, oxygen, carbon dioxide, nitrogen, and other odoriferous gases. Methane (CH4) production is detectable in about one third of healthy adult individuals. In the past years, several studies have been focused on CH4 metabolism at the intestinal level and on the putative association between this gas and the pathophysiology of organic and functional bowel disorders. An overview of the present knowledge about the physiology of CH4 metabolism and its role in intestinal diseases is provided in this report.