Flatulence, Belching, and Abdominal Gas
What causes gas?
Which foods cause gas?
What are some symptoms and problems of gas?
What diagnostic tests are used?
How is gas treated?
Points to remember
Everyone has gas and eliminates it by burping or passing it through the
rectum. However, many people think they have too much gas when they really
have normal amounts. Most people produce about 1 to 3 pints a day and
pass gas about 14 times a day.
Gas is made primarily of odorless vapors--carbon dioxide,
oxygen, nitrogen, hydrogen, and sometimes methane. The unpleasant odor
of flatulence 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.
Gas in the digestive tract (that is, the esophagus, stomach, small intestine,
and large intestine) comes from two sources:
- swallowed air
- 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 stomach also releases carbon dioxide when stomach acid and
bicarbonate mix, 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.
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.
Which foods cause
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.
Beans contain large amounts of this complex sugar. Smaller amounts 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, normally have low levels of the enzyme
lactase needed to digest lactose after childhood. 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 sugarfree candies and gums.
Most starches, including potatoes, corn, noodles, and wheat, produce
gas as 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
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.
some symptoms and problems of gas?
The most common symptoms of gas are flatulence, abdominal bloating, abdominal
pain, and belching. 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.
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
Sometimes a person with chronic belching may have an upper
GI disorder, such as peptic ulcer disease, gastroesophageal reflux disease
(GERD), or gastroparesis.
Occasionally, some people believe that swallowing air
and releasing it will relieve the discomfort of these disorders, and this
person may intentionally or unintentionally develop a habit of belching
to relieve discomfort.
Gas-bloat syndrome may occur after fundoplication 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. It occurs in about 10 percent
of people who have this surgery but may improve with time.
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. Too much gas may be the result of carbohydrate
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
Doctors believe that bloating is usually the result of
an intestinal disorder, such as irritable bowel syndrome (IBS). The cause
of IBS is unknown, but may involve abnormal movements and contractions
of intestinal muscles and increased pain sensitivity in the intestine.
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.
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 pain
is on the left side of the colon, it can be confused with heart disease.
When the pain is on the right side of the colon, it may mimic gallstones
tests are used?
Because gas symptoms may be caused by a serious disorder, those causes
should be ruled out. The doctor usually begins with a review of dietary
habits and symptoms. The doctor may ask the patient to keep a diary of
foods and beverages consumed for a specific time period.
If lactase deficiency is the suspected cause of gas, the
doctor may suggest avoiding milk products for a period of time. A blood
or breath test may be used to diagnose lactose intolerance.
In addition, to determine if someone produces too much
gas in the colon or is unusually sensitive to the passage of normal gas
volumes, the doctor may ask patients to count the number of times they
pass gas during the day and include this information in a diary.
Careful review of diet and the amount of gas passed may
help relate specific foods to symptoms and determine the severity of the
Because the symptoms that people may have are so variable,
the physician may order other types of diagnostic tests in addition to
a physical exam, depending on the patient's symptoms and other factors.
How is gas
Experience has shown that the most common ways to reduce the discomfort
of gas are changing diet, taking medicines, and reducing the amount of
Doctors may tell people 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.
Doctors 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 nonprescription, over-the-counter medicines are available to help
reduce symptoms, including antacids with simethicone. 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. However, these medicines have no
effect on intestinal gas. Dosage varies depending on the form of medication
and the patient's age.
Activated charcoal tablets (Charcocaps) may provide relief
from gas in the colon. Studies have shown that when these tablets are
taken before and after a meal, intestinal gas is greatly reduced. The
usual dose is 2 to 4 tablets taken just before eating and 1 hour after
The 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 (Lactaid and Dairy Ease).
Beano, a newer 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 are added per serving just before eating to break down the gas-producing
sugars. Beano has no effect on gas caused by lactose or fiber.
Doctors may prescribe medicines to help reduce symptoms, especially for
people with a disorder such as IBS.
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 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
- 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 sugarfree 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 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 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
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