Gas

Belching is caused by

• Swallowed air

• Gas generated by carbonated beverages

People normally swallow small amounts of air while eating and drinking. However, some people unconsciously swallow larger amounts of air (aerophagia) repeatedly while eating or smoking and sometimes when they feel anxious or nervous. Excessive salivation, which may occur with gastroesophageal reflux, ill-fitting dentures, certain drugs, gum chewing, or nausea of any cause, also increases air swallowing.

Most swallowed air is later belched up, and very little passes from the stomach into the rest of the digestive system. The small amount of air that does pass into the intestines is mostly absorbed into the bloodstream and very little is passed as flatus.

Flatus results from hydrogen, methane, and carbon dioxide gases that are produced by the bacteria normally present in the large intestine. These bacteria always produce some gas, but excessive gas can be produced

• When people consume certain foods

• When the digestive tract is unable to absorb food properly (malabsorption syndromes)

Malabsorption syndromestropical sprue, celiac disease, and pancreatic insufficiency, also may lead to the production of large amounts of gas.

However, some people may simply have more or different bacteria naturally living in their digestive tract, or they may have a motility (movement) disorder of the muscles in their digestive tract. These variations may account for differences in flatus production. People can record their flatus frequency in a diary before being evaluated by a doctor.

A sensation of bloating or abdominal swelling (distention) can be present in people who have digestive disorders such as poor stomach emptying (gastroparesis) or irritable bowel syndrome or other physical disorders such as ovarian cancer or colon cancer. Many drugs with anticholinergic affects can slow stomach emptying and cause bloating. Sometimes, the sensation is caused by disorders that do not involve the abdomen. For example, in some people, the only symptom of a heart attack is a feeling of bloating or a strong urge to belch. However, many people who feel bloated do not have any physical disorder.

Doctors are not sure what role intestinal gas plays in the sensation of bloating. Aside from people who drink carbonated beverages or swallow excessive air, most people who have a sensation of bloating actually do not have excessive gas in their digestive system. However, studies do show that some people, such as those who have irritable bowel syndrome, are particularly sensitive to normal amounts of gas. Similarly, people with eating disorders (such as anorexia nervosa or bulimia) often misperceive and are particularly stressed by symptoms such as bloating. Thus, the basic abnormality in people with gas-related symptoms may be an intestine that is extremely sensitive (hypersensitive intestine). A motility disorder may contribute to symptoms as well.

In people with gas, certain symptoms and characteristics are cause for concern. They include

• Weight loss (unintentional)

• Blood in stool

• Chest pain

People with a bloating sensation in their chest, especially if the bloating sensation is accompanied by chest pain, should see a doctor promptly because this may be a sign of heart disease. People with any gas-related symptoms who have other warning signs, abdominal discomfort, or diarrhea should see a doctor within a week or so. People who have none of these symptoms or signs should see a doctor at some point, but it is not urgent.

Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the symptoms and the tests that may need to be done ( see Table: Some Causes and Features of Gas-Related Complaints).

For excessive belching, the history is focused on finding the cause of air swallowing, especially dietary causes. For excessive flatus, doctors seek dietary causes and also symptoms of malabsorption (such as diarrhea and/or fatty, foul-smelling stool).

In people with any gas-related complaint, doctors need to understand the relationship between symptoms and meals (both timing and type and amount of food) and bowel movements. Doctors ask people about changes in frequency and color and consistency of stool. Doctors also need to know whether people have lost any weight.

In people with bloating or flatus, the physical examination is focused on finding signs of an underlying physical disorder (such as ovarian cancer). Doctors do abdominal, rectal, and (for women) pelvic examinations.

Doctors do not usually do any testing on people with gas-related complaints unless they have other symptoms that suggest a specific disorder ( see Table: Some Causes and Features of Gas-Related Complaints). For example, people who also have diarrhea may need testing for a malabsorption syndrome.

An exception is middle age or older people who develop persistent bloating or distention, particularly those who have not had digestive system symptoms in the past. For such people, doctors may do tests for cancer of the ovary and/or colon.

Activated charcoal tablets can sometimes help reduce flatus and its unpleasant odor. However, charcoal stains the mouth and clothing. Charcoal-lined undergarments are available.

Probiotics, which are bacteria found naturally in the body that promote the growth of good bacteria, may reduce bloating and flatulence by promoting growth of normal intestinal bacteria in some people.

Some people with indigestion