Is having gas normal or is it a sign of a medical problem?

Everyone has gas and gets rid of it by burping and by passing it through the rectum. Many people think they have too much gas, when most of the time they really have normal amounts. Most people produce about 1 to 3 pints a day and pass gas about 14 to 23 times a day.

Gas is made primarily of odorless vapors -- carbon dioxide, oxygen, nitrogen, hydrogen, and sometimes methane. The unpleasant odor of gas comes from bacteria in the large intestine that release small amounts of gases that contain sulfur.

Although having gas is common, it can be uncomfortable and embarrassing. Understanding causes, ways to reduce symptoms, and treatment will help most people find relief.

What causes gas?

Gas in the digestive tract (that is, the esophagus, stomach, small intestine, and large intestine) comes from the following two sources:

  • Normal breakdown of certain undigested foods by harmless bacteria naturally present in the large intestine (colon).
  • Air swallowing (aerophagia) is a common cause of gas in the stomach. Everyone swallows small amounts of air when eating and drinking. However, eating or 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 body does not digest and absorb all carbohydrates (the sugar, starches and fiber found in many foods) in the small intestine because of a shortage or absence of certain enzymes.

This undigested food then passes from the small intestine into the large intestine. In the large intestine, harmless and normal 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.

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 symptomatic gas in one person may not cause symptoms 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. Furthermore, most people who have symptomatic gas do not have more gas than other people, but rather more sensitivity to symptoms caused by this gas.

Which foods cause gas?

Most foods that contain carbohydrates can cause gas. In contrast, fats, and proteins cause little gas.

Sugars

The sugars that cause gas are raffinose, stachyose, verbascose, lactose, fructose, and sorbitol:

  • Raffinose, stachyose, verbascoce are indigestible oligosaccharides present in large amounts in legumes, especially beans. Smaller amounts of this complex sugar are found in cabbage, brussels sprouts, broccoli, asparagus, other vegetables and whole grains.
  • Lactose is the natural sugar in milk. It is also found in milk products, such as cheese and ice cream, and processed foods, such as bread, cereal, and salad dressing. Many people, particularly those of African, Native American, or Asian background, have low levels of the enzyme lactase needed to digest lactose. Also, as people age, their enzyme levels decrease. As a result, over time people may experience increasing amounts of gas after eating food containing lactose.
  • Fructose is naturally present in onions, artichokes, pears, and wheat. It is also used as a sweetener in some soft drinks and fruit drinks.
  • Sorbitol is a sugar alcohol found naturally in fruits, including apples, pears, peaches, prunes, and some liquid forms of medications. Excess amounts can lead to diarrhea. It is also used as an artificial sweetener in many dietetic foods and sugar-free candies and gums.

Starches

Most starches, including potatoes, corn, noodles and wheat, produce gas. They are broken down in the large intestine. Rice is the only starch that does not cause gas.

Fiber

Many foods contain soluble and insoluble fiber. Soluble fiber dissolves easily in water and takes on a soft, gel-like texture in the intestines. Found in oat bran, beans, peas and most fruits, soluble fiber is not broken down until it reaches the large intestine, where digestion causes gas.

Insoluble fiber, on the other hand, passes essentially unchanged through the intestines and produces little gas. Wheat bran and some vegetables contain this kind of fiber.

What are some symptoms and problems of gas?

The most common symptoms of gas are belching, flatulence, abdominal bloating, and abdominal pain. However, not everyone experiences these symptoms. The determining factors probably are how much gas the body produces, how many fatty acids the body absorbs, and a person's sensitivity to gas in the large intestine. Chronic symptoms caused by too much gas or by a serious disease are rare.

Belching

An occasional belch during or after meals is normal and releases gas when the stomach is full of food. However, people who belch frequently may be swallowing too much air and releasing it before the air enters the stomach. Sometimes a person with chronic belching may have an upper GI disorder, such as peptic ulcer disease, gastroesophageal reflux disease (GERD), or gastritis.

Believing that swallowing air and releasing it will relieve the discomfort of these disorders, this person may unintentionally develop a habitual cycle of belching and discomfort. Frequently, the pain continues or worsens, leading the person to believe he or she has a serious disorder. An extreme example of this is Meganblase syndrome, which causes chronic belching. This syndrome is characterized by severe air swallowing and an enlarged bubble of gas in the stomach following heavy meals. The resulting fullness and shortness of breath may mimic a heart attack.

This gas syndrome is usually correctable by making behavioral changes. Gas-bloat syndrome may occur after surgery to correct GERD. The surgery creates a one-way valve between the esophagus and stomach that allows food and gas to enter the stomach, but often prevents normal belching and the ability to vomit. Surgery may be needed to correct gas-bloat syndrome.

Flatulence

Another common complaint is passage of too much gas through the rectum (flatulence). However, most people do not realize that passing gas 14 to 23 times a day is normal. Although rare, too much gas may be the result of carbohydrate malabsorption or overactive bacteria in the colon.

Abdominal bloating

Many people believe that too much gas causes abdominal bloating. However, people who complain of bloating from gas often have normal amounts and distribution of gas. They actually may be unusually aware of gas in the digestive tract.

Doctors believe that bloating is usually the result of an intestinal motility disorder, such as irritable bowel syndrome (IBS). Motility disorders are characterized by abnormal movements and contractions of intestinal muscles. These disorders may give a false sensation of bloating because of increased sensitivity to gas.

Any disease that causes intestinal obstruction (for example, Crohn's disease or colon cancer) may also cause abdominal bloating. In addition, people who have had many operations, adhesions (scar tissue), or internal hernias may experience bloating or pain. 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 gas collects on the left side of the colon, the pain can be confused with heart disease. When it collects on the right side of the colon, the pain may feel like the pain associated with gallstones or appendicitis.

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