Introductory remarks to intestinal gas metabolism

Different complex and strictly regulated processes are involved in intestinal gas metabolism, and, still now, a full understanding of these mechanisms is lacking. Different techniques have shown that the volume of human intestinal gas is less than 200 mL. The composition of intraluminal gas varies along the entire gastrointestinal tract. More than 99% of the gas is composed of five non-odorous gases (N 2 , O 2 , CO 2 , H 2 and CH 4 ). Various other odoriferous gases are present in trace quantities and account for <1% of flatus. Intestinal gas derives from three sources: swallowed air, intraluminal production (chemical reactions and bacterial metabolism, the latter characterized by both gas production and consumption) and diffusion of gas into the lumen from bloodstream. Stimulating and inhibitory reflexes strictly control gas transit. Gas removal from the intestinal tract occurs by eructation, absorption, bacterial consumption and anal evacuation. A more complete understanding of these physiological mechanisms is required, mainly in order to fully grasp the pathological gas-related conditions.