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Gastrointestinal Gas


Everyone has gas and eliminates it by burping or passing it through the rectum (flatus).


Most people produce about 1 to 3 pints a day and pass gas about 14 times a day. However, many people think that they have too much gas, when they really have normal amounts.

Gas is made primarily of odorless vapors - carbon dioxide, nitrogen, hydrogen, and sometimes methane. The unpleasant odor of flatulence comes from bacteria in the large intestine that release small amounts of gases that contain sulfur. Although having gas is common, it can be uncomfortable and embarrassing.

Gas in the digestive tract comes from two sources:

  • Swallowed air
  • Normal breakdown of certain undigested foods by harmless bacteria naturally present in the large intestine

Swallowed air. Air swallowing (aerophagia) is a common cause of air in the stomach. Everyone swallows small amounts of air when eating and drinking. However, eating and drinking rapidly, chewing gum, using a straw to drink, smoking, and wearing loose dentures can cause some people to take in more air. Burping, or belching, is the way most swallowed air - which contains nitrogen, oxygen, and carbon dioxide - leaves the stomach. The remaining gas moves into the small intestine where it is partly absorbed. A small amount travels to the large intestine for release through the rectum.

Breakdown of undigested foods. The body does not digest and absorb some carbohydrates (the sugar, starches and fiber found in many foods) in the small intestine because of a shortage or absence of certain enzymes. This undigested food then passes from the small intestine into the large intestine, where harmless and normal bacteria break down the food, producing hydrogen, carbon dioxide and, in about one-third of all people, methane. Eventually, these gases pass through the rectum. Most foods that contain carbohydrates can cause gas. By contrast, fats and proteins cause little gas.


The most common symptoms of gas are belching, flatulence, abdominal bloating, and abdominal pain. However, not everybody experiences these symptoms. The determining factors probably are how much gas the body produces and a person's sensitivity to gas in the large intestine.

Excessive amounts of flatus may suggest malabsorption, especially if accompanied by diarrhea or weight loss.


The diagnosis is made by medical history and supported by the physical examination.


The most common ways to reduce the discomfort of gas are changing diet, taking medicines, and reducing the amount of air swallowed.

Diet. An initial trial of a lactose-free diet may be attempted. Common gas-producing foods include brown beans, cauliflower, brussels sprouts, broccoli, cabbage, onions, beer, red wine, and eggs. Your doctor may recommend an elimination trial in which certain foods are eliminated from the diet. Doctors may also suggest limiting high-fat foods to reduce bloating and discomfort. This helps the stomach to empty faster, allowing gas to move into the small intestine.

Nonprescription medicines. Many nonprescription, over-the-counter medicines are available to help reduce symptoms, including antacids with simethicone and activated charcoal. The effectiveness of these medications is unclear. Digestive enzymes, such as lactase supplements, actually help digest carbohydrates and may allow people to eat foods that normally cause gas. Beano reduces gas production associated with baked beans.

Reducing the amount of air swallowed (aerophagia). Since aerophagia may be due to excessive salivation, it is important to avoid habits like excessive gum chewing or smoking and to treat digestive diseases (e.g., peptic ulcer) that may cause hypersalivation as well as disorders that may cause nausea and reflex salivation.

It is important to chew food and to eat food slowly. Do not drink through a straw. When belching is associated with use of carbonated beverages or antacids, these should be avoided.

When aerophagia is troublesome, clamping a pencil or other object between the teeth may decrease the amount of involuntary or habit swallowing and break the cycle of aerophagia-discomfort-belch-relief.


What causes gas?

What foods are gas-producing?

Should I eliminate any foods?

How do I prevent aerophagia?