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Intestinal gas and bloating

Diane Abraczinskas, MD
Section Editor
Nicholas J Talley, MD, PhD
Deputy Editor
Shilpa Grover, MD, MPH


A variety of gastrointestinal complaints, such as belching, bloating, abdominal pain, constipation, or flatulence, are commonly attributed by the patient to "excess gas," even though this perception is usually incorrect. When excessive intestinal gas does occur, it may be due to excessive air swallowing, increased intraluminal production from malabsorbed nutrients, decreased gas absorption due to obstruction, or expansion of intraluminal gas due to changes in atmospheric pressure (table 1). The understanding of intestinal gas syndromes has been aided by studies of intestinal gas composition and volume in normal individuals and in those with complaints of "too much gas."


The volume of gas in the intestinal tract, as determined by body plethysmography or argon washout techniques, is approximately 200 mL in both the fasting and postprandial states [1,2], and in subjects who complain of gaseous distention [3]. Quantitative measurement of bowel gas has also been performed with digitized abdominal radiographs [4].


Nitrogen (N2), oxygen (O2), carbon dioxide (CO2), hydrogen (H2), and methane (CH4) account for more that 99 percent of expelled intestinal gas [1]. One investigation using a gas washout technique revealed the composition of gas within the intestinal tract of 10 normal subjects to be predominantly N2 [1]. Oxygen was present in very low concentrations, and the concentrations of CO2, H2, and CH4 were variable.

The composition of gas may vary in a given compartment of the gastrointestinal tract. As an example, stomach gas contains high concentrations of N2 and O2 similar to the atmosphere, while flatus contains less O2 and more CH4.

None of the principal gases has an odor. Minor constituents of flatus, to which odor may be attributable, include sulfur-containing compounds such as methanethiol, dimethyl sulfide, hydrogen sulfide [5,6], as well as short-chain fatty acids, skatoles, indoles, volatile amines, and ammonia.


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Literature review current through: Sep 2016. | This topic last updated: May 12, 2016.
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