Flatulence

Flatulence is the sensation of an increased amount of gas in the digestive tract.
Increased amounts of gas can gather in the stomach or farther along the digestive tract. Excess gas is expelled through the mouth (belching) or through the anus (known colloquially as farting and called flatus by doctors), or it is absorbed through the walls of the digestive tract into the blood and then excreted by the lungs. Bacteria in the digestive system also break down (metabolize) some gases.
Air is a gas, which can be swallowed with food. Swallowing small amounts of air is normal, but some people unconsciously swallow large amounts (aerophagia) , especially when they feel anxious. Most swallowed air is later belched up, so only some air passes from the stomach into the rest of the digestive system. Swallowing large amounts of air may make a person feel full, and the person may belch excessively or pass the air through the anus.
Other gases are produced in the digestive system by several means. Hydrogen, methane, and carbon dioxide are produced by bacterial metabolism of food in the intestine, especially after a person eats certain foods such as beans and cabbage. People who have deficiencies of the enzymes that break down certain sugars also tend to produce large amounts of gas when they eat foods containing these sugars. Lactase deficiency, tropical sprue, and pancreatic insufficiency all may lead to the production of large amounts of gas. People with irritable bowel syndrome do not produce large amounts of gas, although the passage of normal volumes of gas through the bowel may be changed. Almost anyone who eats large amounts of proteins or fruits will develop some degree of flatulence.

Symptoms
Flatulence is often associated with abdominal pain and bloating; however, the exact relationship between flatulence and any of these symptoms is not really known. Some people appear to be particularly sensitive to the effects of gas in the digestive system; others can tolerate large amounts without developing any symptoms.
Belching is more likely to occur shortly after eating or during periods of stress. Drinking carbonated beverages sometimes leads to belching. Some people feel a tightness in their chest or stomach just before belching that is relieved as the gas is expelled.
People normally pass gas through the anus more than 10 times a day, but flatulence may cause a person to pass gas more often. Gas passed through the anus may or may not have an odor. On occasion, fecal incontinence occurs as a person tries to pass gas, only to be surprised by the expulsion of stool as well.
Infants with crampy abdominal pain sometimes pass excessive amounts of gas. Whether these children actually produce more gas than others or are simply more sensitive to gas is not clear.

Treatment
Bloating and belching are difficult to relieve. If belching is the main problem, reducing the amount of air being swallowed can help, which is difficult because people generally are not aware of swallowing air. Avoiding chewing gum and eating more slowly in a relaxed atmosphere may help.
People who belch or pass gas excessively may need to change their diet by avoiding foods that are difficult to digest. Discovering which foods are causing the problem may require eliminating one food or one group of foods at a time. A person can start by eliminating milk and dairy products, then fresh fruits, and then certain vegetables and other foods. Avoiding carbonated beverages helps some people. Although drugs generally are not very effective, simethicone, which is present in some antacids and is also available separately, can provide a little relief. Sometimes other drugs-including other types of antacids (including those that contain baking soda), metoclopramide, and bethanechol- may help. Aromatic oils, such as peppermint oil, help some people, especially those who experience cramps with flatulence. Eating more fiber helps some people but worsens the symptoms in others. Chlorophyll, an ingredient in many over-the-counter products, and charcoal tablets do not ecrease flatulence but help reduce its offensive odor.
[Merck]