Digestive Disorders

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 3 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. Gases that contain sulfur often produce the 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:

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 sugarfree 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, and 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?
The following are the most common symptoms for gas, however, each individual may experience symptoms differently. Chronic symptoms caused by too much gas or by a serious disease are rare. Although not everyone experiences them, the most common symptoms of gas are:

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.

Chronic belching may also indicate an upper GI disorder, such as peptic ulcer disease, gastroesophageal reflux disease (GERD), or gastritis.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, rare, chronic gas syndromes associated with belching include:

Meganblase syndrome causes chronic belching. It is characterized by severe air swallowing and an enlarged bubble of gas in the stomach following heavy meals. Fullness and shortness of breath caused by this disorder may mimic a heart attack.

Gas-bloat syndrome may occur after surgery to correct GERD. The surgery creates a one-way valve between the esophagus and stomach that allows food and gas to enter the stomach.

flatulence
Passing gas through the rectum is called flatulence. Passing gas 14 to 23 times a day is considered normal.

abdominal bloating
Bloating is usually the result of an intestinal motility disorder, such as irritable bowel syndrome (IBS). Motility disorders are characterized by abnormal movements and contractions of intestinal muscles. These disorders may give a false sensation of bloating because of an increased sensitivity to gas.

Splenic-flexure syndrome is a chronic disorder that may be caused by gas trapped at bends (flexures) in the colon.

Crohn's disease or colon cancer, or any disease that causes intestinal obstruction, may also cause abdominal bloating.

Internal hernias or adhesions (scar tissue) from surgery may cause bloating or pain.

Fatty foods can delay stomach emptying and cause bloating and discomfort, but not necessarily too much gas.

abdominal pain and discomfort
Gas in the intestine causes pain for some people. When it collects on the left side of the colon, the pain can be confused with heart disease. When it collects on the right side of the colon, the pain may feel like the pain associated with gallstones or appendicitis.

The symptoms of gas may resemble other conditions or medical problems. Consult your physician for a diagnosis.

How is gas in the digestive tract diagnosed?
Symptoms of gas may be caused by a serious disorder, which should be determined. In addition to a complete medical history and physical examination, your physician may suggest the following activities to assist in the diagnosis:

food diary
You may be asked to keep a diary of foods and beverages consumed for a specific time period, or to count the number of times you pass gas during the day.
sigmoidoscopy or colonoscopy
For people 50 years of age and older, and for those with a family history, the possibility of colorectal cancer is considered. A colon examination (sigmoidoscopy or colonoscopy) may be requested.
upper GI (gastrointestinal) series
For chronic belching, your physician will look for signs or causes of excessive air swallowing and may request an upper GI series -- an x-ray to view the esophagus, stomach, and upper small intestine.

Treatment for gas in the digestive tract
Specific treatment will be determined by your physician(s) based on:

your age, overall health, and medical history
extent of the disorder
your tolerance for specific medications, procedures, or therapies
expectations for the course of the disorder
your opinion or preference

The most common ways to reduce the discomfort of gas are:

changes in the diet
medications
reducing the amount of air swallowed

This page was last updated on: January 24, 2008.

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