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 14-23 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. By contrast, fats and proteins cause little gas.
The sugars that cause gas are raffinose, lactose, fructose and sorbitol.
- Raffinose is present in large amounts in 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 found naturally in fruits, including apples, pears, peaches and prunes. It is also used as an artificial sweetener in many dietetic foods and sugar-free candies and gums.
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.
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.
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.
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.
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.
What diagnostic tests are used?
Although gas is very common, at times medical evaluation is necessary. Weight loss, anemia, fevers, diarrhea, or blood in the stool should result in early evaluation. The evaluation usually begins with a review of dietary habits and symptoms. Your doctor may ask you to keep a diary of foods and beverages consumed for a specific time period.
If lactase deficiency is the suspected cause of gas, your doctor may suggest avoiding milk products for a period of time. A blood or breath test may be used to diagnose lactose intolerance.
Other breath tests may be obtained to determine if there is fructose malabsorption or overgrowth of intestinal bacteria.
Careful review of diet and the amount of gas passed may help relate specific foods to symptoms and determine the severity of the problem.
If a patient complains of bloating, the doctor may examine the abdomen for the sound of fluid movement to rule out ascites (build-up of fluid in the abdomen). The doctor also may do an exam for signs of inflammation to rule out diseases of the colon.
The possibility of colon cancer is usually evaluated in people 50 years of age and older. This possibility also is evaluated in those with a family history of colorectal cancer, especially if they have never had a colon examination (sigmoidoscopy or colonoscopy). These tests may also be appropriate for someone with unexplained weight loss, diarrhea, or blood not visible (occult blood) in the stool.
For those with chronic belching, the doctor will look for signs or causes of excessive air swallowing. If needed, an upper GI series (X-ray to view the esophagus, stomach, and small intestine) may be performed to rule out disease.
How is gas treated?
Most of the time, treatment of the symptoms of gas requires an approach that includes both dietary adjustment and medication. The most common ways to reduce the discomfort of gas are changing diet, taking medication, and reducing the amount of air swallowed.
Your doctor may tell you to eat fewer foods that cause gas. However, for some people this may mean cutting out healthy foods, such as fruits and vegetables, whole grains, and milk products.
Your doctor may also suggest limiting high-fat foods to reduce bloating and discomfort. This helps the stomach empty faster, allowing gases to move into the small intestine.
Unfortunately, the amount of gas caused by certain foods varies from person to person. Effective dietary changes depend on learning through trial and error how much of the offending foods one can handle.
Many non-prescription, over-the-counter medicines are available to help reduce symptoms. Such medicines include antacids with simethicone and activated charcoal. Digestive enzymes, such as lactase supplements, actually help digest carbohydrates and may allow people to eat foods that normally cause gas.
Antacids, such as Mylanta II®, Maalox II ® and Di-Gel®, contain simethicone, a foaming agent that joins gas bubbles in the stomach so that gas is more easily belched away. The recommended dose is 2 to 4 tablespoons of the simethicone preparation taken 1/2 to 2 hours after meals.
Activated charcoal tablets may provide relief from gas in the colon. Studies have shown that intestinal gas is greatly reduced when these are taken before and after a meal. The usual dose is 2 to 4 tablets taken just before eating and 1 hour after meals.
For those with lactose intolerance, enzyme lactase--which aids with lactose digestion--is available in liquid and tablet form without a prescription (Lactaid®, Lactrase®, and Dairy Ease®). Adding a few drops of liquid lactase to milk before drinking it or chewing lactase tablets just before eating helps digest foods that contain lactose. Also, lactose-reduced milk and other products are available at many grocery stores.
Beano®, an over-the-counter digestive aid, contains the sugar-digesting enzyme that the body lacks to digest the sugar in beans and many vegetables. The enzyme comes in liquid form. Three to 10 drops per serving are added to food just before eating to break down the gas-producing sugars. Beano has no effect on gas caused by lactose or fiber.
Probiotics are healthy bacteria that can be found in yogurt and over-the-counter supplements. It may also improve gas symptoms by changing the bacterial flora that is responsible for producing some of the gas.
If one suffers from constipation, treatment of this disorder will be important to improve gas passage from the intestinal tract.
As for the discomfort of gas related to failure to advance the gas through the gastrointestinal tract, gentle exercise is important to stimulate the intestines to pass the gas through. At times, abdominal massage may also improve symptoms.
Doctors may prescribe medicines to help reduce symptoms, especially for people with a motility disorder, such as IBS. If bacterial overgrowth in the small intestines is demonstrated by testing, antibiotics to reduce these bacteria may be prescribed.
Reducing swallowed air
For those who have chronic belching, doctors may suggest ways to reduce the amount of air swallowed. Recommendations are to avoid chewing gum and to avoid eating hard candy. Eating at a slow pace and checking with a dentist to make sure dentures fit properly should also help.
Although gas may be uncomfortable and embarrassing, it is not life-threatening. Understanding the causes, ways to reduce symptoms, and treatment will help most people find some relief.
Points to remember
- Everyone has gas in the digestive tract.
- People often believe normal passage of gas to be excessive.
- Gas comes from two main sources: swallowed air and normal breakdown of certain foods by harmless bacteria naturally present in the large intestine.
- Many foods with carbohydrates can cause gas. Fats and proteins cause little gas.
- Foods that may cause gas include the following:
- Vegetables, such as broccoli, cabbage, Brussels sprouts, onions, artichokes, and asparagus
- Fruits, such as pears, apples, and peaches
- Whole grains, such as whole wheat and bran
- Soft drinks and fruit drinks
- Milk and milk products, such as cheese and ice cream, and packaged foods prepared with lactose, such as bread, cereal, and salad dressing
- Foods containing sorbitol, such as dietetic foods and sugar-free candies and gums
- The most common symptoms of gas are belching, flatulence, bloating, and abdominal pain. However, some of these symptoms are often caused by an intestinal motility disorder, such as irritable bowel syndrome, rather than too much gas.
- The most common ways to reduce the discomfort of gas are changing diet, taking nonprescription or prescription medicines, and reducing the amount of air swallowed.
- Digestive enzymes, such as lactase supplements, actually help digest carbohydrates and may allow people to eat foods that normally cause gas in specific individuals with lactose intolerance.
- National Digestive Diseases Information Clearinghouse (NDDIC). What I need to know about Gas Accessed 10/14/2013.
- American Gastroenterological Association. Living with Gas in the Digestive Tract Accessed 10/14/2013.
- American College of Gastroenterology. Belching, Bloating and Flatulence Accessed 10/14/2013.
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 10/1/2013...#7314