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Medical Author:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In this Article

• Intestinal gas facts
• What causes belching?
• What causes bloating?
• What causes flatulence (gas)?
• What are the causes of intermittent abdominal bloating/distention?
• How is belching, bloating/distention, and flatulence evaluated?
• How is excessive intestinal gas treated?
• Patient Comments: Intestinal Gas - Effective Treatments
• Patient Comments: Intestinal Gas - Bloating Causes
• Patient Comments: Intestinal Gas - Causes
• Intestinal Gas (Belching, Bloating, Flatulence) Index

Excessive production of gas

Excessive production of gas by bacteria is a common cause of intermittent abdominal bloating/distention. Bacteria can produce too much gas in three ways.

• First, the amount of gas that bacteria produce varies from individual to individual. In other words, some individuals may have bacteria that produce more gas, either because there are more of the bacteria or because their particular bacteria are better at producing gas.
• Second, there may be poor digestion and absorption of foods in the small intestine, allowing more undigested food to reach the bacteria in the colon. The more undigested food the bacteria have, the more gas they produce. Examples of diseases of that involve poor digestion and absorption include lactose intolerance, pancreatic insufficiency, and celiac disease.
• Third, bacterial overgrowth can occur in the small intestine. Under normal conditions, the bacteria that produce gas are limited to the colon. In some conditions, these bacteria spread into the small intestine. When this bacterial spread occurs, food reaches the bacteria before it can be fully digested and absorbed by the small intestine. Therefore, the bacteria in the small intestine have a lot of undigested food from which to form gas. This condition in which the gas-producing bacteria move into the small intestine is called bacterial overgrowth of the small intestine (bowel).

Excessive production of gas by bacteria usually is accompanied by flatulence. Increased flatulence may not always occur; however, since gas potentially can be eliminated in other ways such as absorption into the body, utilization by other bacteria, or possibly, by elimination at night without the awareness of the gas-passer.

Physical obstruction

An obstruction (blockage) can occur virtually anywhere from the stomach to the rectum. When the blockage is temporary or partial, it can cause intermittent abdominal bloating/distention. For example, scarring of the pylorus (pyloric stenosis) can obstruct the opening from the stomach into the intestines, thereby blocking the complete emptying of the stomach. After meals, the stomach is normally filled with food and swallowed air. Then, during the next hour or two, the stomach secretes acid and fluid, which mix with the food and assist in digestion. As a result, the stomach distends further. When the obstruction is incomplete, the food, air, and fluid eventually pass into the intestines and the bloating/distention resolves.

An obstruction in the small bowel, which is most commonly due to adhesions from a previous surgery, is another cause of intermittent abdominal distention. To make matters worse, the distention that is caused by the physical obstruction stimulates both the stomach and intestines to secrete fluid, which adds to the distention.

Severe constipation or fecal impaction (hardened stool in the rectum) can also obstruct the flow of the intestinal contents and result in distention. In this case, however, the bloating/distention usually is constant and progressive and is relieved by bowel movements or removal of the impacted stool.

Functional obstruction

A functional obstruction is not caused by an actual physical blockage, but rather by the poor functioning of the muscles of the stomach or intestines that propel the intestinal contents. When these muscles are not working normally, the intestinal contents will accumulate and distend the abdomen. Examples of functional obstruction include:

• gastroparesis (paralysis of the stomach) of diabetes;
• chronic intestinal pseudo-obstruction, an unusual condition in which the muscles of the small intestine do not work normally; and
• Hirschsprung's disease, in which a small stretch of colonic muscle does not contract normally due to missing nerves.

There is accumulating scientific evidence that some patients with abdominal bloating and distention due to gas may have a functional abnormality of the intestinal muscles that prevents gas from being normally transported through the intestine and expelled. Instead, their gas accumulates in the intestine. Among patients with irritable bowel syndrome (IBS) with abdominal bloating or distention as an important symptom, the gas accumulates in the small intestine and not the colon. The gas accumulates during the day and is greatest in the evening.

Fats in food have an effect on the intestine that mimics a functional obstruction. Dietary fat reaching the small intestine causes transport of digesting food, gas, and liquid within the intestines to slow. This can promote the accumulation of food, gas, and liquid and lead to bloating and/or distention.

Dietary fiber or fiber used for treating constipation can cause bloating without increasing the production of gas in the intestine. It is believed that this sensation of bloating (and possibly even distention) is caused by the slowed passage of gas through the intestine which is caused by fiber. Of course, some types of fiber may lead to increased production of gas because they are digested to some extent by the colonic bacteria.

Intestinal hypersensitivity

Some people appear to be very sensitive (hypersensitive) to distention of their intestines, and they may feel bloated even with normal amounts of digesting food, gas, and fluid in the intestine after a meal. The bloating may be aggravated or even progress to distention if the meal contains substantial amounts of fat, perhaps because fat slows the transit of gas and digesting food through the stomach and small intestine.