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Gas in the Digestive Tract

Upper GI - Athens GI Center
       The digestive tract

Gas is air in the digestive tract—the large, muscular tube that extends from the mouth to the anus, where the movement of muscles, along with the release of hormones and enzymes, allows for the digestion of food. Gas leaves the body when people burp through the mouth or pass gas through the anus.

Gas is primarily composed of carbon dioxide, oxygen, nitrogen, hydrogen, and sometimes methane. Flatus, gas passed through the anus, may also contain small amounts of gasses that contain sulfur. Flatus that contains more sulfur gasses has more odor.

Everyone has gas. However, many people think they burp or pass gas too often and that they have too much gas. Having too much gas is rare.

What causes gas?

Gas in the digestive tract is usually caused by swallowing air and by the breakdown of certain foods in the large intestine by bacteria.

Everyone swallows a small amount of air when eating and drinking. The amount of air swallowed increases when people

Burping allows some gas to leave the stomach. The remaining gas moves into the small intestine, where it is partially absorbed. A small amount travels into the large intestine for release through the anus.

The stomach and small intestine do not fully digest some carbohydrates—sugars, starches, and fiber found in many foods. This undigested food passes through the small intestine to the large intestine. Once there, undigested carbohydrates are broken down by bacteria in the large intestine, which release hydrogen and carbon dioxide in the process. Other types of bacteria in the large intestine take in hydrogen gas and create methane gas or hydrogen sulfide, the most common sulfur gas in flatus.

Studies have detected methane in the breath of 30 to 62 percent of healthy adults.1 A larger percentage of adults may produce methane in the intestines, but the levels may be too low to be detected. Research suggests that people with conditions that cause constipation are more likely to produce detectable amounts of methane.1 More research is needed to find out the reasons for differences in methane production and to explore the relationship between methane and other health problems.

Some of the gas produced in the intestines is absorbed by the bloodstream and carried to the lungs, where it is released in the breath.

Normally, few bacteria live in the small intestine. Small intestinal bacterial overgrowth is an increase in the number of bacteria or a change in the type of bacteria in the small intestine. These bacteria can produce excess gas and may also cause diarrhea and weight loss. Small intestinal bacterial overgrowth is usually related to diseases or disorders that damage the digestive system or affect how it works, such as Crohn’s disease—an inflammatory bowel disease that causes inflammation, or swelling, and irritation of any part of the gastrointestinal (GI) tract—or diabetes.

1- Sahakian AB, Jee SR, Pimentel M. Methane and the gastrointestinal tract. Digestive Diseases and Sciences. 2010;55(8):2135–43. Epub 2009 Oct 15

What are the symptoms of gas?

The most common symptoms of gas are burping, passing gas, bloating, and abdominal pain or discomfort. However, not everyone experiences these symptoms.

Burping. Burping, or belching, once in a while, especially during and after meals, is normal. However, people who burp frequently may be swallowing too much air and releasing it before the air enters the stomach.

Some people who burp frequently may have an upper GI disorder, such as gastroesophageal reflux disease—a chronic condition in which stomach contents flow back up into the esophagus. People may believe that swallowing air and releasing it will relieve the discomfort, and they may intentionally or unintentionally develop a habit of burping to relieve discomfort.

Passing gas. Passing gas around 13 to 21 times a day is normal.2 Flatulence is excessive gas in the stomach or intestine that can cause bloating and flatus. Flatulence may be the result of problems digesting certain carbohydrates.

Bloating. Bloating is a feeling of fullness and swelling in the abdomen, the area between the chest and hips. Problems digesting carbohydrates may cause increased gas and bloating. However, bloating is not always caused by too much gas. Bloating may result from diseases that affect how gas moves through the intestines, such as rapid gastric emptying, or from diseases that cause intestinal obstruction, such as colon cancer. People who have had many operations, internal hernias, or bands of internal scar tissue called adhesions may experience bloating.

Disorders such as irritable bowel syndrome (IBS) can affect how gas moves through the intestines or increase pain sensitivity in the intestines. IBS is a functional GI disorder, meaning that the symptoms are caused by changes in how the digestive tract works. The most common symptoms of IBS are abdominal pain or discomfort, often reported as cramping, along with diarrhea, constipation, or both. IBS may give a sensation of bloating because of increased sensitivity to normal amounts of gas.

Eating a lot of fatty food can delay stomach emptying and cause bloating and discomfort, but not necessarily too much gas.

Abdominal pain and discomfort. People may feel abdominal pain or discomfort when gas does not move through the intestines normally. People with IBS may be more sensitive to gas and feel pain when gas is present in the intestines.

2- Gas-related complaints. The Merck Manuals Online Medical Library. site icon. Updated October 2007. Accessed June 26, 2012.

How is gas treated?

Gas can be treated by reducing swallowed air, making dietary changes, or taking over-the-counter or prescription medications. People who think they have too much gas can try to treat gas on their own before seeing a health care provider. Health care providers can provide advice about reducing gas and prescribe medications that may help.

Reducing swallowed air. Swallowing less air may help reduce gas, especially for people who burp frequently. A health care provider may suggest eating more slowly, avoiding gum and hard candies, or checking with a dentist to make sure dentures fit correctly.

Making dietary changes. People may be able to reduce gas by eating less of the foods that cause gas. However, many healthy foods may cause gas, such as fruits and vegetables, whole grains, and milk products. The amount of gas caused by certain foods varies from person to person. Effective dietary changes depend on learning through trial and error which foods cause a person to have gas and how much of the offending foods one can handle.

While fat does not cause gas, limiting high-fat foods can help reduce bloating and discomfort. Less fat in the diet helps the stomach empty faster, allowing gases to move more quickly into the small intestine.

Taking over-the-counter medications. Some over-the-counter medications can help reduce gas or the symptoms associated with gas:

Taking prescription medications. Health care providers may prescribe medications to help reduce symptoms, especially for people with small intestinal bacterial overgrowth or IBS.


If you have any questions or wish to schedule an appointment, please do not hesitate to call the office at (706) 548-0058. Remember that we usually require that you see a primary care physician (your family doctor or PCP) before we can schedule you. If you are having a medical emergency, get medical attention immediately at your nearest healthcare provider:

Athens Regional Medical Center: (706) 475-7000
St. Mary's Hospital: (706) 354-3000


This informational material is taken from the National Digestive Diseases Information Clearinghouse, a division of the U.S. Department of Health and Human Resources.

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