Gas In 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.
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.
1Sahakian AB, Jee SR, Pimentel M. Methane and the gastrointestinal tract. Digestive Diseases and Sciences. 2010;55(8):2135–43. Epub 2009 Oct 15.
Most foods that contain carbohydrates can cause gas. In contrast, fats and proteins cause little gas. Foods that produce gas in one person may not cause gas in someone else, depending on how well individuals digest carbohydrates and the type of bacteria present in the intestines.
Some foods that may cause gas include:
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.
2Gas-related complaints. The Merck Manuals Online Medical Library. Updated October 2007. Accessed June 26, 2012.
Because gas symptoms may be caused by a serious disorder, those causes should be ruled out. Health professionals usually begin with a review of dietary habits and symptoms. The health professional may ask the patient to keep a diary of foods and beverages consumed for a specific time period.
If lactase deficiency is the suspected cause of gas, the health professional may suggest avoiding milk products for a period of time. A blood or breath test may be used to diagnose lactose intolerance.
In addition, to determine if someone produces too much gas in the colon or is unusually sensitive to the passage of normal gas volumes, the health professional may ask a patient to count the number of times they pass gas during the day and include this information in a diary.
Careful review of diet and the amount of gas passed may help relate specific foods to symptoms and determine the severity of the problem.
Because the symptoms that people may have are so variable, the health professional may order other types of diagnostic tests in addition to a physical exam, depending on the patient's symptoms and other factors.
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. For more information about IBS, see the Irritable Bowel Syndrome fact sheet from the National Digestive Diseases Information Clearinghouse at http://www.digestive.niddk.nih.gov/.
People’s eating habits and diet affect the amount of gas they have. For example, eating and drinking too fast may increase the amount of air swallowed, and foods that contain carbohydrates may cause some people to have more gas.
Tracking eating habits and symptoms can help identify the foods that cause more gas. Avoiding or eating less of these foods may help reduce gas symptoms.
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) sponsors research into digestive conditions, including gas. Researchers are studying disorders that may cause gas symptoms, such as IBS.
The NIDDK and other components of the National Institutes of Health (NIH) are conducting clinical trials aimed at improving the diagnosis and treatment of IBS. Self Administered Cognitive Behavior Therapy for Irritable Bowel Syndrome, funded under NIH clinical trial number NCT00738920, assesses the short- and long-term efficacy of cognitive behavior therapy for IBS using two treatment delivery systems: self administered and therapist administered. Long-term project goals include development of an effective self-administered behavioral treatment program that can enhance quality of patient care, improve clinical outcomes, and decrease the economic and personal costs of IBS.
Safety Study of Probiotics in Adults with Irritable Bowel Syndrome, funded under NIH clinical trial number NCT00971711, is a phase I study of the safety and effectiveness of VSL#3 in adults with IBS. VSL#3 is a high-potency probiotic medical food that is commercially available. Acupuncture/Moxibustion for Irritable Bowel Syndrome (Acu/MoxalIBS), funded under NIH clinical trial number NCT00945074, tests the efficacy of acupuncture in combination with moxibustion for symptom improvement in adults with IBS. Moxibustion is the application of heat from a burning herb at the acupuncture point. All participants will receive moxibustion and will be assigned to one of three treatment protocols: standard acupuncture, individualized acupuncture, and sham acupuncture.
Participants in clinical trials can play a more active role in their own health care, gain access to new research treatments before they are widely available, and help others by contributing to medical research. For information about current studies, visit http://www.clinicaltrials.gov/.
Academy of Nutrition and Dietetics
120 South Riverside Plaza, Suite 2000
Chicago, IL 60606–6995
Internet: http://www.eatright.org/ (Click on “Find a Registered Dietitian”)
International Foundation for Functional Gastrointestinal Disorders
P.O. Box 170864
Milwaukee, WI 53217–8076
Phone: 1–888–964–2001 or 414–964–1799
The National Digestive Diseases Information Clearinghouse (NDDIC) is a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The NIDDK is part of the National Institutes of Health of the U.S. Department of Health and Human Services. Established in 1980, the Clearinghouse provides information about digestive diseases to people with digestive disorders and to their families, health care professionals, and the public. The NDDIC answers inquiries, develops and distributes publications, and works closely with professional and patient organizations and Government agencies to coordinate resources about digestive diseases.
This publication is not copyrighted. The Clearinghouse encourages users of this publication to duplicate and distribute as many copies as desired.
Publications produced by the Clearinghouse are carefully reviewed by both NIDDK scientists and outside experts. This publication was reviewed by Brooks D. Cash, M.D., F.A.C.P., F.A.C.G., National Naval Medical Center.
NIH Publication No. 13–883
Page last updated January 2, 2013