Health Information

Gas in the Digestive Tract

What is gas in the digestive tract?

Gas in the digestive tract is created from:
  • swallowing air.
  • the breakdown of certain foods by the bacteria that are present in the colon.

Everyone has gas. It may be uncomfortable and embarrassing, but it is not life-threatening. Gas is eliminated by burping or passing it through the rectum. Most people produce about 1 to 4 pints of gas a day and pass gas about 14 times a day.

Most gas is made up of odorless vapors - carbon dioxide, oxygen, nitrogen, hydrogen, and sometimes methane. Bacteria in the large intestine release gases that contain sulfur and produce an unpleasant odor of flatulence.

What causes gas in the digestive tract?

Gas in the digestive tract comes from two sources:
  • aerophagia (air swallowing) - usually caused by eating or drinking rapidly, as well as by chewing gum, smoking, or wearing loose dentures.
Belching is the way most swallowed air leaves the stomach. The remaining gas is partially absorbed into the small intestine and a small amount goes into the large intestine and is released through the rectum.
  • breakdown of certain undigested foods by harmless bacteria naturally present in the large intestine (colon)

Some carbohydrates (sugar, starches, and fiber) are not digested or absorbed in the small intestine because of a shortage or absence of certain enzymes. The undigested or unabsorbed food then passes into the large intestine, where harmless and normal bacteria break down the food. This process produces hydrogen, carbon dioxide, and, in about one-third of all people, methane gases, which are released through the rectum.

Foods that commonly cause gas:

According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), most foods that contain carbohydrates can cause gas, and fats and proteins cause little gas. Foods that cause gas include the following:
  • raffinose - a complex sugar found in beans, cabbage, Brussels sprouts, broccoli, asparagus, other vegetables, and whole grains.
  • lactose - a natural sugar found in milk and milk products, such as cheese and ice cream, and in processed foods, such as bread, cereal, and salad dressing.
  • fructose - a sugar found in onions, artichokes, pears, and wheat, and is also used as a sweetener in some soft drinks and fruit drinks.
  • sorbitol - a sugar found naturally in fruits, including apples, pears, peaches, and prunes, and is also used as an artificial sweetener in many dietetic foods and sugar-free candies and gums.
  • starches - most starches, including potatoes, corn, noodles, and wheat produce gas as they are broken down in the large intestine. (Rice is the only starch that does not cause gas.)
  • soluble fiber - fiber that dissolves easily in water and takes on a soft, gel-like texture in the intestines; is found in oat bran, beans, peas, and most fruits.
  • insoluble fiber - fiber, such as that found in wheat bran and some vegetables, which passes essentially unchanged through the intestines and produces little gas.

What are the symptoms of gas?

Chronic symptoms caused by too much gas or by a serious disease are rare. The following are the most common symptoms of gas. However, each individual may experience symptoms differently. Symptoms may include:

  • belching
    Belching during or after meals is normal, but people who belch frequently may be swallowing too much air and releasing it before the air enters the stomach.