Gas in the digestive tract—the esophagus, stomach, small intestine, and large intestine—comes from two sources:

• Swallowed Air is a common cause of gas in the stomach. Everyone swallows small amount of air when eating and drinking rapidly, chewing gum, smoking, or wearing loose dentures can cause some people to take in more air. Burping, or belching, is the way most swallowed air—which contains nitrogen, oxygen, and carbon dioxide—leaves the stomach.

The remaining gas moves into the small intestine, where it is partially absorbed. A small amount travels into the large intestine for release through the rectum. The stomach also releases carbon dioxide when stomach acid mixes with the bicarbonate in digestive juices, but most of this gas is absorbed into the bloodstream and does not enter the large intestine.

• Breakdown of Undigested Foods - the body does not digest and absorb some carbohydrates—the sugar, starches, and fiber found in many foods—in the small intestine because of a shortage or absence of certain enzymes that aid digestion. This undigested food then passes from the small intestine into the large intestine, where normal, harmless bacteria break down the food, producing hydrogen, carbon dioxide, and, in about one-third of all people, methane.

Eventually these gases exit through the rectum. People who make methane do not necessarily pass more gas or have unique symptoms. A person who produces methane will have stools that consistently float in water. Research has not shown why some people produce methane and others do not. Foods that produce gas in one person may not cause gas in another. Some common bacteria in the large intestine can destroy the hydrogen that other bacteria produce. The balance of the two types of bacteria may explain why some people have more gas than others.
 

Belching

• An occasional belch during or after meals is normal and releases gas when the stomach is full of food. Sometimes a person with chronic belching may have an upper gastrointestinal (GI) disorder, such as peptic ulcer, gastroesophageal reflux disease (GERD), delayed gastric emptying.
  Sometimes people believe that swallowing air and releasing it will relieve the discomfort of these disorders, and they may intentionally or unintentionally develop a habit of belching to relieve discomfort.

Flatulence

• Another common complaint is too much flatulence. However, most people do not realize that passing gas 14 to 23 times a day is normal. Too much gas may be the result of carbohydrate malabsorption.

Abdominal Bloating

• Abdominal bloating is usually the result of an intestinal disorder, such as irritable bowel syndrome (IBS). The cause of irritable bowel syndrome (IBS) is unknown but may involve abnormal movements and contractions of intestinal muscles and increased pain sensitivity in the intestines. These disorders may give a sensation of bloating because of increased sensitivity to gas. Any disease that causes intestinal inflammation or obstruction, such as Crohn’s disease or colon cancer, may also cause abdominal bloating. Finally, eating a lot of fatty food can delay stomach emptying and cause bloating and discomfort, but not necessarily too much gas.

Abdominal Pain and Discomfort

• Some people have pain when gas is present in the intestine. When pain is on the left side of the colon, it can be confused with heart disease, which sometimes causes abdominal pain. When the pain is on the right side of the colon, it may mimic gallstones or appendicitis.

• Breath testing is a noninvasive way to help doctors diagnose a number of conditions. By analyzing your breath, we can measure the amount of certain gases, allowing doctors to arrive at a diagnosis quickly and accurately.
• Lactose Intolerance Breath Test: the body is unable to digest lactose, a sugar found in milk and milk products. In order to diagnose lactose intolerance.
• Fructose Intolerance Breath Test: this test determines whether you have difficulty absorbing fructose, a sugar found in onions, artichokes, pears and wheat. It is also used as a sweetener in some drinks. If you have symptoms such as bloating, gas, cramping and diarrhea, it may be due to fructose malabsorption.
• Bacterial Overgrowth Syndrome (SIBO): Bacteria growing uncontrolled in the small intestine can cause small intestine bacterial overgrowth (SIBO). You may experience excessive bloating, gas, cramping and diarrhea.