Dr. MJ Bazos MD,
Gas in the
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
- 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 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.
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
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 gas.
fiber, on the other hand, passes essentially unchanged through the intestines
and produces little gas. Wheat bran and some vegetables contain this kind of
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
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.
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.
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.
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
What Diagnostic Tests
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
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
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
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.
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 and activated charcoal. Digestive enzymes, such as lactase
supplements, actually help digest carbohydrates and may allow people to eat
foods that normally cause gas.
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
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.
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.
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
1. Everyone has gas in the digestive tract.
2. People often believe normal passage of gas to
3. Gas comes from two main sources: swallowed
air and normal breakdown of certain foods by harmless bacteria naturally present
in the large intestine.
4. Many foods with carbohydrates can cause gas.
Fats and proteins cause little gas.
5. 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
- Foods containing sorbitol, such as dietetic foods
and sugarfree candies and gums.
7. 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.
8. Digestive enzymes, such as lactase
supplements, actually help digest carbohydrates and may allow people to eat
foods that normally cause gas.