Gas In The Digestive Tract
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.
What Causes Gas?
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).
Swallowed air
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 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.
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 Gas?
Most foods that contain carbohydrates can cause gas. By contrast, fats and
proteins cause little gas.
Sugars
The sugars that cause gas are: raffinose, lactose, fructose, and sorbitol.
Raffinose
Beans contain large amounts of this complex sugar. Smaller amounts are
found in cabbage, brussels sprouts, broccoli, asparagus, other vegetables,
and whole grains.
Lactose
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
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
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.
Starches
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.
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.
Two rare chronic gas syndromes are associated with belching: Meganblase
syndrome and gas-bloat syndrome. The Meganblase syndrome, which causes
chronic belching, 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.
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.
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
severe 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 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.
Splenic-flexure syndrome is a chronic disorder that seems to be caused
by trapped gas at bends (flexures) in the colon. Symptoms include
bloating, muscle spasms, and upper abdominal discomfort. Splenic-flexure
syndrome often accompanies IBS.
Any disease that causes intestinal 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 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?
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 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) and for signs of inflammation to rule out diseases of the
colon.
The possibility of colon cancer is usually considered in people 50
years of age and older and in those with a family history of colorectal
cancer, particularly 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 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 upper small intestine) may be
performed to rule out disease.
How Is Gas Treated?
The most common ways to reduce the discomfort of gas are changing diet,
taking medicines, and reducing the amount of air swallowed.
Diet
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.
Nonprescription medicines
Many nonprescription, over-the-counter medicines are available to help
reduce symptoms, including 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. However, these medicines have no effect
on intestinal gas. The recommended dose is 2 to 4 tablespoons of the
simethicone preparation taken 1/2 to 2 hours after meals.
Activated charcoal tablets (Charcocaps) may provide relief from gas in
the colon. Studies have shown that when 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 meals.
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.
Prescription medicines
Doctors may prescribe medicines to help reduce symptoms, especially for
people with a motility disorder, such as IBS. Promotility or prokinetic
drugs, such as metoclopramide (Reglan) and cisapride (Propulsid), may move
gas through the digestive tract quickly.
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.
Conclusion
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:
-
- Beans
- 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
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.
Source: National
Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health
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