Some people feel that they pass too much gas (flatulence) or burp too frequently, both of which can be a source of embarrassment and discomfort. Studies show that the average adult produces about one to three pints of gas each day, which is passed through the anus 14 to 23 times per day. Burping occasionally before or after meals is also normal.

The amount of gas produced depends upon a person’s diet and individual factors. However, most people who complain of excessive gas do not produce more gas than the average person. Instead, they often have an increased awareness of normal amounts of gas.

On the other hand, several foods and medical conditions can cause excessive gas production. This topic reviews the sources of intestinal gas, conditions that increase sensitivity to gas, and measures to reduce gas production.

SOURCES OF GAS

There are two primary sources of intestinal gas: gas that is ingested (mostly swallowed air) and gas that is produced by bacteria in the colon.

Air swallowing – Air swallowing is the major source of gas in the stomach. It is normal to swallow a small amount of air when eating and drinking and when swallowing saliva. Larger amounts of air may be swallowed when eating food rapidly, gulping liquids, chewing gum, , sucking on candy, or smoking.

Most swallowed air is eliminated by belching, so that only a relatively small amount passes from the stomach into the small intestine. However, posture may influence how much air passes to the small intestine. In an upright position, most swallowed air passes back up the esophagus and is expelled through the mouth. On the other hand, when lying down, swallowed air tends to pass into the small intestine. Some of the oxygen and nitrogen in swallowed air may be absorbed through the walls of the GI tract into the blood.

Belching may be voluntary or occur unintentionally. Involuntary belching is a normal process that typically occurs after eating to relieve air that enlarges or stretches the stomach. In addition, belching may increase with certain foods that relax the ring-shaped muscle (sphincter) around the lower end of the esophagus where it joins the stomach. Such foods include peppermint, chocolate, and fats.

Bacterial production – The colon normally provides a home for billions of harmless bacteria, some of which support the health of the bowel. Carbohydrates are normally digested by enzymes in the small intestine. However, certain carbohydrates are incompletely digested, allowing bacteria in the colon to digest them. The by-products of bacterial digestion include odorless vapors, such as carbon dioxide, hydrogen, and methane. Minor components of flatus (gas expelled through the anus) have an unpleasant odor, including trace amounts of sulfur-containing gases that are released by bacteria in the large intestine.

CAUSES OF GAS

Some carbohydrates, are not well digested, and therefore produce increased amounts of gas. A number of vegetables contain complex carbohydrates, such as cabbage, Brussels sprouts, asparagus, broccoli, and some whole grains. As a result, these foods tend to cause increased amounts of gas and flatulence.

Lactose (milk) intolerance is caused by an impaired ability to digest lactose, the principle sugar in dairy products (show table 1). Symptoms of lactose intolerance include diarrhea, abdominal pain, and flatulence after consuming milk or milk-containing products. In Europe and the United States, lactose intolerance affects 7 to 20 percent of people who are white, 80 to 95 percent of Native Americans, 65 to 75 percent of Africans and African Americans, and 50 percent of Hispanics. More than 90 percent of people in some regions of eastern Asia have lactose intolerance.

Intolerance to other sugars— In addition to lactose and raffinose, some people are intolerant of other sugars contained in foods. Two common examples are fructose (contained in dried fruit, honey, sucrose, onions, artichokes, and many foods and drinks that contain “high fructose corn syrup”) and sorbitol (a sugar substitute contained in some sugar free candies and chewing gum).

Certain diseases can also cause excessive bloating and gas. For example, people with diabetes or scleroderma may, over time, have slowing in the peristaltic (forward propulsion) activity of the small intestine. This may lead to bacterial overgrowth within the bowel, with poor digestion of carbohydrates and other nutrients. Patients with reduced absorption of foods, such as celiac disease or pancreatic disease, often complain of gas.

Many people with irritable bowel syndrome (IBS) are sensitive to normal amounts of gas. Nerves that carry sensory messages from the bowel may be overactive in people with IBS, so that normal amounts of gas or movement in the gastrointestinal tract are perceived as excessive and painful. Some people with severe IBS feel better when treated with medications that decrease the perception of painful sensations coming from the intestine.

Aerophagia— Chronic, repeated belching usually occurs when a person frequently swallows large amounts of air (ie, aerophagia). Aerophagia is typically an unconscious process. The diagnosis is made after excluding other possible causes (such as gastroesophageal reflux disease). Treatment focuses on decreasing air swallowing by eating slowly without gulping and avoiding carbonated beverages, chewing gum, and smoking.

TREATMENT

Avoid foods that appear to aggravate symptoms. These may include milk and dairy products, certain fruits or vegetables, whole grains, artificial sweeteners, and/or carbonated beverages. A record of foods and beverages consumed over a certain time period may help to pinpoint which foods are bothersome. Foods that can cause gas include beans, cabbage, cauliflower, Brussels sprouts, broccoli, and asparagus. Potatoes, corn, noodles, and wheat produce gas while rice does not. Soluble fiber (found in oat bran, peas and other legumes, beans, and most fruit) also causes gas. Avoiding these foods or eating them infrequently may reduce gas production.

Try an over-the-counter product that contains simethicone, such as certain antacids (eg, Maalox Anti-Gas, Mylanta Gas, Gas-X, Phazyme). Simethicone causes gas bubbles to break up and is widely used to relieve gas, although its benefit is questionable.

Try an over-the-counter product that contains activated charcoal (eg, Charcocaps, CharcoAid) may help some people.

Try Beano™, an over-the-counter preparation that contains an enzyme (alpha-galactosidase) that helps to breakdown certain complex carbohydrates. This agent may be effective in reducing gas production and frequency in people who have increased gas after eating beans or other vegetables that contain raffinose.

Try restricting lactose in the diet and/or use a lactose-digestive aid (eg, LactAide ). People who avoid dairy products should take a calcium supplement.