Gas in the GI Tract

Gas in the gastrointestinal (GI) tract comes from swallowed air and from digestion, which is the mechanical and chemical break down of food. The process of digestion produces a number of gases, including oxygen, nitrogen, hydrogen, carbon dioxide, and others. Gas in the GI tract can cause gas pains, bloating, belching, and flatulence.

Gases are eliminated from the body through the mouth (i.e., by burping or belching) or through the rectum and anus (i.e., flatulence). Most GI gases are odorless. Odor in gas is caused by bacteria. Most people pass gas an average of 14 times per day.

Air that is swallowed, for example, during eating and drinking, talking, and chewing gum, enters the stomach. This gas, which often contains oxygen, carbon dioxide, and nitrogen, usually is eliminated from the stomach through belching (burping). Small amounts of stomach gas enter the small intestine and are eventually eliminated through flatulence or are absorbed into the bloodstream.

Some foods, such as complex carbohydrates (e.g., sugar, starch, fiber) are not fully digested in the small intestine. These foods pass into the large intestine (also called the large bowel or colon) and are broken down by bacteria, producing flatulence that is eliminated from the body through the rectum and anus.

Foods that are high in protein (e.g., lean meats, poultry) or fat (e.g., nuts) do not typically produce large amounts of gas in the GI tract during digestion. Foods that commonly do produce gas include the following:

  • Beans
  • Fruits (e.g., apples, pears, peaches) and fruit juice
  • Milk and dairy products (e.g., cheese, ice cream)
  • Vegetables (e.g., asparagus, broccoli, cabbage, corn, potatoes, onions)
  • Whole grain (e.g., wheat, oat) products

Gas in the digestive tract may not cause symptoms, other than the normal passing of gas. In some cases, gas can cause abdominal pain or discomfort, excessive belching or flatulence, and abdominal bloating. These symptoms can indicate a more serious disorder, such as peptic ulcer disease, gastroesophageal reflux disease (GERD), intestinal obstruction, or malabsorption syndromes (e.g., lactose intolerance).

Bloating, which is a symptom of abnormal digestion, is characterized by abdominal pain and distention (i.e., stretching, swelling, expanding). Conditions that may cause bloating include irritable bowel syndrome, Crohn's disease, and colorectal cancer.

Sometimes, gas pain can be mistaken for another condition, such as appendicitis, gallstones, or even heart attack. To make a diagnosis, physicians usually take a medical history, including a food diary (list of all foods and beverages consumed) and a history of symptoms. If a certain food (e.g., milk) is thought to be the cause for GI gas symptoms, the patient may be advised to avoid that food for a period of time to see if symptoms improve.

Other diagnostic tests may be used to rule out serious conditions. These tests include blood tests (e.g., to detect celiac disease), urea breath test (UBT; used to detect H. pylori bacteria), endoscopic procedures (e.g., colonoscopy; used to view the inside of the colon), and imaging tests (e.g., ultrasound, CT scan; used to detect blockages or tumors).

In most cases, belching, flatulence, gas pains, and bloating can be reduced by dietary changes (i.e., avoiding foods that cause excess gas) and over-the-counter medications (e.g., antacids, Lactaid, Beano). Avoiding talking while eating and gum chewing and eating more slowly also may be helpful.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 28 Feb 2008

Last Modified: 17 Sep 2015