INTRODUCTION
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. 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, or smoking.
Most swallowed air is eliminated by belching (or "eructation"), so that only a relatively small amount passes from the stomach into the small intestine (
show figure 1
). 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 release 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.
Some carbohydrates, such as raffinose, are not well digested, and therefore produce increased amounts of gas. A number of vegetables contain raffinose, 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.
Some individuals are not able to digest certain carbohydrates. A classic example is lactose, the major sugar contained in dairy products (
show table 1
). Thus, consuming large amounts of lactose may lead to increased gas production, along with cramping and diarrhea (
see "Lactose intolerance" below
).
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.
SYMPTOMS
Some people feel they pass an excessive amount of gas from below or burp too frequently. Other people notice abdominal distension and crampy abdominal pain. Such pain may be perceived in areas where gas can become trapped (
show figure 1
), such as in bends in the colon, which occur naturally in the area under the liver (upper to mid right part of the abdomen), and in the area under the spleen (upper to mid left part of the abdomen).
SENSITIVITY TO GAS
The link between flatulence, belching, and the actual amount of gas in the intestines is not always clear. The vast majority of people who complain about gas-related symptoms do not have an excessive amount of gas in the intestine, but rather they have an increased awareness of normal amounts of gas in the intestine. This can happen in a variety of circumstances.
Irritable bowel syndrome
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. The primary symptoms of IBS are abdominal pain and altered bowel habits. Many patients also complain of abdominal distension. (
See "Patient information: Irritable bowel syndrome"
).
Some people with severe IBS feel better when treated with medications that decrease the perception of painful sensations coming from the intestine (such as low doses of imipramine or nortriptyline).
Functional dyspepsia
Dyspepsia is the term for recurrent or persistent pain or discomfort in the upper abdomen. Approximately 25 percent of people in the United States and other western countries experience dyspepsia. (
See "Patient information: Abdominal pain (functional dyspepsia) in adults"
).
Dyspepsia can arise from various underlying conditions, the most common of which is "functional" (or "nonulcer") dyspepsia. Functional dyspepsia causes abdominal pain without an identifiable cause, probably due to an increased sensitivity to gas in the upper intestines.
Irritation of the anus or esophagus
People who have irritation around their anus due to external hemorrhoids or other problems may also experience more discomfort when they pass gas. Similarly, people who have irritation of the esophagus (esophagitis) may find burping painful. (
See "Patient information: Hemorrhoids"
).
CAUSES OF INCREASED GAS
The vast majority of people with gas-related complaints do not produce excessive amounts of gas. However, there are several conditions that may lead to increased gas formation.
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.
Foods that cause gas
Several foods contain the carbohydrate raffinose, which is poorly digested and increases gas production. Foods containing raffinose include beans, cabbage, cauliflower, Brussels sprouts, broccoli, and asparagus. Avoiding these foods or eating them infrequently may reduce gas production.
Starch and soluble fiber can also contribute to gas formation. 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. Some laxatives contain soluble fiber and may cause gas, particularly during the first few weeks of use.
Lactose intolerance
Intolerance to lactose-containing foods (primarily dairy products) is a common problem. 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.
Lactose intolerance is caused by an impaired ability to digest lactose, the principle sugar in dairy products (
show table 1
). Clinical symptoms of lactose intolerance include diarrhea, abdominal pain, and flatulence after consuming milk or milk-containing products.
Lactose intolerance can be diagnosed by a lactose breath test, in which lactose in consumed and the amount of hydrogen in the breath is measured. Treatment involves avoidance of dairy products that contain lactose and/or use of supplements that contain the enzyme lactase (available in over-the-counter products such as Lactaidÿ). People who avoid dairy products should take a supplement that contains 1000 mg of calcium and 400 IU vitamin D since dairy products are a primary source of these important substances. This is especially true for children and women. (
See "Patient information: Calcium and Vitamin D for bone health"
).
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).
Diseases associated with increased gas
A number of diseases can cause impaired absorption of carbohydrates (carbohydrate malabsorption), which can lead to increased gas. In addition to bacterial overgrowth described above, carbohydrate malabsorption can occur in people with celiac disease (a disease caused by intolerance to a protein contained in wheat), short bowel syndrome, and those who have rare primary disorders of the enzymes needed to digest specific forms of carbohydrates. (
See "Patient information: Celiac disease"
).
DIAGNOSIS
The first steps in evaluating a person who feels excessive gas include a thorough medical history and physical examination. Additional testing depends upon an individual's situation. People with "alarm" symptoms such as diarrhea, weight loss, abdominal pain, anemia, blood in the stool, lack of appetite, fever, or vomiting usually require specific testing. In people without alarm symptoms, further testing is not usually helpful.
Specific tests may include:
- Examination of stool to detect the presence of blood, abnormally increased levels of fat (steatorrhea), or the presence of a parasite, Giardia lamblia.
- A lactose tolerance test, during which a person drinks a test dose of lactose. Breath or blood samples are obtained to confirm the presence of lactose intolerance.
- X-ray examination of the small intestine.
TREATMENT
A clinician may recommend several measures to help reduce bothersome gas and the associated discomfort or distress. The approach depends upon the individual's symptoms and the cause. Specific recommendations may include:
- 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.
- Try an over-the-counter product that contains simethicone, such as certain antacids (eg, Maaloxÿ Anti-Gas, Mylantaÿ Gas, Gas-Xÿ, Phazymeÿ). 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, Charcocapsÿ, CharcoAidÿ). Evidence concerning the benefit of activated charcoal is contradictory: its benefit has been supported by some studies and refuted by others. It is reasonable to try.
- 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 bismuth subsalicylate (eg, Pepto-Bismolÿ) to reduce the odor of unpleasant smelling gas due to hydrogen sulfide, a sulfur-containing compound.
- An antibiotic may be prescribed if a healthcare provider suspects bacterial overgrowth is present.
- Restrict lactose in the diet and use a lactose-digestive aid, such as lactose-reduced milk or over-the-counter "lactase" supplements (eg, LactAidÿ tablets or liquid). People who avoid dairy products should take a calcium supplement.
- Consider an external device to deodorize flatus, such as underwear made from carbon fiber (eg, Underease protective underwear {Under-Tec, Corp} and GasMedicÿ underair brief {Dairiair, LLC}). These appear to be effective but are expensive. Charcoal lined cushions or pads are also available, but may not be as effective.