Irritable Bowel Syndrome
Irritable bowel syndrome (IBS) is a disorder
that interferes with the normal functions of the large intestine
(colon). It is characterized by a group of symptoms-crampy abdominal
pain, bloating, constipation, and diarrhea.
One in five Americans has IBS, making it one of
the most common disorders diagnosed by doctors. It occurs more often
in women than in men, and it usually begins around age
IBS causes a great deal of discomfort and
distress, but it does not permanently harm the intestines and does
not lead to intestinal bleeding or to any serious disease such as
cancer. Most people can control their symptoms with diet, stress
management, and medications prescribed by their physician. But for
some people, IBS can be disabling. They may be unable to work, go to
social events, or travel even short distances.
What causes IBS?
What causes one person to have IBS and not
another? No one knows. Symptoms cannot be traced to a single organic
cause. Research suggests that people with IBS seem to have a colon
that is more sensitive and reactive than usual to a variety of
things, including certain foods and stress. Some evidence indicates
that the immune system, which fights infection, is also involved.
IBS symptoms result from the following:
- The normal motility of the colon may not work
properly. It can be spasmodic or can even stop temporarily. Spasms
are sudden strong muscle contractions that come and go.
- The lining of the colon (epithelium), which
is affected by the immune and nervous systems, regulates the
passage of fluids in and out of the colon. In IBS, the epithelium
appears to work properly. However, fast movement of the colon's
contents can overcome the absorptive capacity of the colon. The
result is too much fluid in the stool. In other patients, colonic
movement is too slow, too much fluid is absorbed, and constipation
- The colon responds strongly to stimuli (for
example, foods or stress) that would not bother most people.
In people with IBS, stress and emotions can
strongly affect the colon. It has many nerves that connect it to the
brain. Like the heart and the lungs, the colon is partly controlled
by the autonomic nervous system, which has been proven to respond to
stress. For example, when you are frightened, your heart beats
faster, your blood pressure may go up, or you may gasp. The colon
responds to stress also. It may contract too much or too little. It
may absorb too much water or too little.
Research has shown that very mild or hidden
(occult) celiac disease is present in a smaller group of people with
symptoms that mimic IBS. People with celiac disease cannot digest
gluten, which is present in wheat, rye, barley, and possibly oats.
Foods containing gluten are toxic to these people, and their immune
system responds by damaging the small intestine. A blood test can
determine whether celiac disease is present. (For information about
celiac disease, see the Celiac
Disease fact sheet from the National Institute of Diabetes
and Digestive and Kidney Diseases (NIDDK).)
The following have been associated with a
worsening of IBS symptoms:
- large meals
- bloating from gas in the colon
- wheat, rye, barley, chocolate, milk products,
- drinks with caffeine, such as coffee, tea, or
- stress, conflict, or emotional upsets
Researchers have also found that women with IBS
may have more symptoms during their menstrual periods, suggesting
that reproductive hormones can exacerbate IBS problems.
What does the colon do?
The colon, which is about 5 feet long, connects
the small intestine with the rectum and anus. The major function of
the colon is to absorb water, nutrients, and salts from the
partially digested food that enters from the small intestine. Two
pints of liquid matter enter the colon from the small intestine each
day. Stool volume is a third of a pint. The difference in volume
represents what the colon absorbs each day.
Colon motility (the contraction of the colon
muscles and the movement of its contents) is controlled by nerves
and hormones and by electrical activity in the colon muscle.
Contractions move the contents slowly back and forth but mainly
toward the rectum. During this passage, water and nutrients are
absorbed into the body. What remains is stool. A few times each day,
strong muscle contractions move down the colon, pushing the stool
ahead of them. Some of these strong contractions result in a bowel
movement. The muscles of the pelvis and anal sphincters have to
relax at the right time to allow the stool to be expelled. If the
muscles of the colon, sphincters, and pelvis do not contract in a
coordinated way, the contents do not move smoothly, resulting in
abdominal pain, cramps, constipation or diarrhea, and a sense of
incomplete stool movement.
What are the symptoms of IBS?
Abdominal pain or discomfort in association with
bowel dysfunction is the main symptom. Symptoms may vary from person
to person. Some people have constipation (hard, difficult-to-pass,
or infrequent bowel movements); others have diarrhea (frequent loose
stools, often with an urgent need to move the bowels); and still
others experience alternating constipation and diarrhea. Some people
experience bloating, which is gas building up in the intestines and
causing the feeling of pressure inside the abdomen.
IBS affects the motility or movement of stool
and gas through the colon and how fluids are absorbed. When stool
remains in the colon for a long time, too much water is absorbed
from it. Then it becomes hard and difficult to pass. Or spasms push
the stool through the colon too fast for the fluid to be absorbed,
resulting in diarrhea. In addition, with spasms, gas may get trapped
in one area or stool may collect in one place, temporarily unable to
Sometimes people with IBS have a crampy urge to
move their bowels but cannot do so or pass mucus with their bowel
Bleeding, fever, weight loss, and persistent
severe pain are not symptoms of IBS and may indicate other problems
such as inflammation or rarely cancer.
How is IBS diagnosed?
If you think you have IBS, seeing your doctor is
the first step. IBS is generally diagnosed on the basis of a
complete medical history that includes a careful description of
symptoms and a physical examination.
No particular test is specific for IBS. However,
diagnostic tests may be performed to rule out other diseases. These
tests may include stool or blood tests, x rays, or endoscopy
(viewing the colon through a flexible tube inserted through the
anus). If these tests are all negative, the doctor may diagnose IBS
based on your symptoms: that is, how often you have had abdominal
pain or discomfort during the past year, when the pain starts and
stops in relation to bowel function, and how your bowel frequency
and stool consistency are altered.
Criteria for IBS Diagnosis
- Abdominal pain or discomfort for at least 12
weeks out of the previous 12 months. These 12 weeks do not have to
- The abdominal pain or discomfort has two of
the following three features:
- It is relieved by having a bowel
- When it starts, there is a change in how
often you have a bowel movement.
- When it starts, there is a change in the
form of the stool or the way it looks.
What is the treatment for IBS?
No cure has been found for IBS, but many options
are available to treat the symptoms. Your doctor will give you the
best treatments available for your particular symptoms and encourage
you to manage stress and make changes to your diet.
Medications are an important part of relieving
symptoms. Your doctor may suggest fiber supplements or occasional
laxatives for constipation, as well as medicines to decrease
diarrhea, tranquilizers to calm you, or drugs that control colon
muscle spasms to reduce abdominal pain. Antidepressants may also
relieve some symptoms. Medications available to treat IBS
specifically are the following:
- Alosetron hydrochloride (Lotronex) has been
re-approved by the U.S. Food and Drug Administration (FDA) for
women with severe IBS who have not responded to conventional
therapy and whose primary symptom is diarrhea. However, even in
these patients, it should be used with caution because it can have
serious side effects, such as severe constipation or decreased
blood flow to the colon.
- Tegaserod maleate (Zelnorm) has been approved
by the FDA for the short-term treatment (usually 4 weeks) of women
with IBS whose primary symptom is constipation.
With any medication, even over-the-counter
medications such as laxatives and fiber supplements, it is important
to follow your doctor's instructions. Laxatives can be habit forming
if they are not used carefully or are used too
It is also important to note that medications
affect people differently and that no one medication or combination
of medications will work for everyone with IBS. You need to work
with your doctor to find the best combination of medicine, diet,
counseling, and support to control your symptoms.
How does stress affect IBS?
Stress-feeling mentally or emotionally tense,
troubled, angry, or overwhelmed-stimulates colon spasms in people
with IBS. The colon has a vast supply of nerves that connect it to
the brain. These nerves control the normal rhythmic contractions of
the colon and cause abdominal discomfort at stressful times. People
often experience cramps or "butterflies" when they are nervous or
upset. But with IBS, the colon can be overly responsive to even
slight conflict or stress. Stress also makes the mind more tuned to
the sensations that arise in the colon and makes the stressed person
perceive these sensations as unpleasant.
Some evidence suggests that IBS is affected by
the immune system, which fights infection in the body. The immune
system is also affected by stress. For all these reasons, stress
management is an important part of treatment for IBS. Stress
- stress reduction (relaxation) training and
relaxation therapies, such as meditation
- counseling and support
- regular exercise such as walking or
- changes to the stressful situations in your
- adequate sleep
Can changes in diet help IBS?
For many people, careful eating reduces IBS
symptoms. Before changing your diet, keep a journal noting the foods
that seem to cause distress. Then discuss your findings with your
doctor. You may also want to consult a registered dietitian, who can
help you make changes to your diet. For instance, if dairy products
cause your symptoms to flare up, you can try eating less of those
foods. You might be able to tolerate yogurt better than other dairy
products because it contains bacteria that supply the enzyme needed
to digest lactose, the sugar found in milk products. Dairy products
are an important source of calcium and other nutrients. If you need
to avoid dairy products, be sure to get adequate nutrients in the
foods you substitute or take supplements.
In many cases, dietary fiber may lessen IBS
symptoms, particularly constipation. However, it may not help pain
or diarrhea. Whole grain breads and cereals, fruits, and vegetables
are good sources of fiber. High-fiber diets keep the colon mildly
distended, which may help prevent spasms. Some forms of fiber also
keep water in the stool, thereby preventing hard stools that are
difficult to pass. Doctors usually recommend a diet with enough
fiber to produce soft, painless bowel movements. High-fiber diets
may cause gas and bloating, but these symptoms often go away within
a few weeks as your body adjusts. (For information about diets for
people with celiac disease, please see the Celiac
Disease fact sheet from NIDDK.)
Drinking six to eight glasses of plain water a
day is important, especially if you have diarrhea. But drinking
carbonated beverages, such as sodas, may result in gas and cause
discomfort. Chewing gum and eating too quickly can lead to
swallowing air, which again leads to gas.
Also, large meals can cause cramping and
diarrhea, so eating smaller meals more often or eating smaller
portions should help IBS symptoms. It may also help if your meals
are low in fat and high in carbohydrates, such as pasta, rice,
whole-grain breads and cereals (unless you have celiac disease),
fruits, and vegetables.
Is IBS linked to other diseases?
IBS itself is not a disease. As its name
indicates, it is a syndrome-a combination of signs and
symptoms. But IBS has not been shown to lead to any serious, organic
diseases, including cancer. Through the years, IBS has been called
by many names, among them colitis, mucous colitis, spastic colon, or
spastic bowel. However, no link has been established between IBS and
inflammatory bowel diseases such as Crohn's disease or ulcerative
Hope Through Research
The NIDDK conducts and supports research into
many kinds of digestive disorders, including IBS. Researchers are
studying gastrointestinal motility and sensitivity to find possible
treatments for IBS. These studies include the structure and
contraction of gastrointestinal muscles as well as the mechanics of
fluid movement through the intestines. Understanding the influence
of the nerves, hormones, and inflammation in IBS may lead to new
treatments to better control the symptoms.
Points to Remember
- IBS is a disorder that interferes with the
normal functions of the colon. The symptoms are crampy abdominal
pain, bloating, constipation, and diarrhea.
- IBS is a common disorder found more often in
women than in men and usually begins around age
- People with IBS have colons that are more
sensitive and react to things that might not bother other people,
such as stress, large meals, gas, medicines, certain foods,
caffeine, or alcohol.
- IBS is diagnosed by its symptoms and by the
absence of other diseases.
- Most people can control their symptoms by
taking medicines (laxatives, antidiarrhea medicines,
tranquilizers, or antidepressants), reducing stress, and changing
- IBS does not harm the intestines and does not
lead to cancer. It is not related to Crohn's disease or ulcerative
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NIH Publication No. 03-693