Medical Author: William C. Shiel Jr., MD, FACP, FACR
Gas or "intestinal gas" means different things to different people. Everyone has gas and eliminates it by belching or passing it through the rectum, medically referred to as flatulence (slang, farting).
The ability to belch is almost universal. Belching, also known as burping, is the act of expelling gas from the stomach out through the mouth. The usual cause of belching is a distended (inflated) stomach caused by swallowed air. The distention of the stomach causes abdominal discomfort, and the belching expels the air and relieves the discomfort. The common reasons for swallowing large amounts of air (aerophagia) are gulping food or drink too rapidly, anxiety, and carbonated beverages.
Excessive air in the stomach is not the only cause of belching. For some people, belching becomes a habit and does not reflect the amount of air in their stomachs. For others, belching is a response to any type of abdominal discomfort and not just to discomfort due to increased gas.
Most people produce 1 to 3 pints of intestinal gas in their large intestines (colons) every 24 hours and pass gas an average of 14 times a day. The gas is made up primarily of carbon dioxide, hydrogen, and in some families, methane, that is mixed with nitrogen and oxygen from room air that is inhaled or swallowed. The carbon dioxide, hydrogen, and methane are produced by bacteria in the large intestine while they digest undigested food that reaches the large intestine. Although these gases are odorless, the bacteria also may produce small amounts of sulfur-containing gases that are foul-smelling. It is important to distinguish between increased flatulence (farting) and foul-smelling flatulence.
Bloating is the subjective sensation (feeling) that the abdomen is larger than normal. Thus, bloating is a symptom akin to the symptom of discomfort. In contrast, distention is the objective determination (physical finding) that the abdomen is actually larger than normal. Bloating and distention may be due to increased amounts of gas in the abdomen, but there also are other causes. Sometimes intestinal gas that is associated with bloating can be accompanied by
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.
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