Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
Irritable bowel syndrome (IBS) is a functional disease, that is, a disease in
which the intestine (bowel) functions abnormally.
Theories of the cause of IBS include abnormal input
from intestinal sensory nerves, abnormal processing of input from the sensory
nerves, and abnormal stimulation of the intestines by the motor nerves.
The primary symptoms of IBS are constipation,
diarrhea, and abdominal pain. Secondary symptoms include abnormal passage of
stool, abnormal form of stool, increased amounts of mucus in the stool, and a
subjective feeling of abdominal distention (bloating).
IBS is diagnosed on the basis of typical symptoms
(Rome Criteria) and the absence of other intestinal and non-intestinal
diseases that may give rise to the symptoms. Testing in IBS is directed
primarily at excluding the presence of other intestinal diseases and
Treatment of IBS consists primarily of medications to
control constipation, diarrhea, and abdominal pain. Anti-depressant medication
and psychological treatments also may be used. It is not clear if dietary
alterations have much effect on the symptoms of IBS except for increases in
dietary fiber, which may improve constipation.
Although it has been hypothesized that IBS may be
caused by intestinal bacteria, specifically by small intestinal bacterial
overgrowth, there is little rigorous scientific support for the hypothesis.
On the other hand, there are a limited number of rigorous scientific studies
demonstrating that probiotics and antibiotics improve the symptoms of IBS.
Future advances in the treatment of IBS depend on a clearer
understanding of its cause(s).
What is irritable bowel syndrome (IBS)?
Irritable bowel syndrome (IBS) is one of the most common ailments of the
bowel (intestines) and affects an estimated 15% of people in the US. The term,
irritable bowel, is not a particularly accurate one since it implies that the bowel
is responding irritably to normal stimuli, and this may or may not be the case.
The several terms used for IBS, including spastic colon,
spastic colitis, and mucous
colitis, attest to the difficulty of getting a descriptive handle on the
ailment. Moreover, each of the other names is itself as problematic as the term
IBS is best described as a functional disease. The concept of functional
disease is particularly useful when discussing diseases of the gastrointestinal
tract. The concept applies to the muscular organs of the gastrointestinal tract;
the esophagus, stomach, small intestine, gallbladder, and colon. What is meant
by the term, functional, is that either the muscles of the organs or the nerves
that control the organs are not working normally, and, as a result, the organs
do not function normally. The nerves that control the organs include not only
the nerves that lie within the muscles of the organs but also the nerves of the
spinal cord and brain to which they are connected.
Some gastrointestinal diseases can be seen and diagnosed with the naked eye,
such as ulcers of the stomach when visualized by certain methods. Thus, ulcers can be seen at surgery, on
and at endoscopy. Other diseases cannot be seen with the naked eye but can be
seen and diagnosed under the microscope. For example, celiac disease and
collagenous colitis are diagnosed by microscopic examination of biopsies of the
small intestine and colon, respectively. In contrast, gastrointestinal functional
diseases cannot be seen with the naked eye or with the microscope. In some
instances, the abnormal function can be demonstrated by tests, for example,
gastric emptying studies or antro-duodenal motility studies. However, these
tests often are complex, are not widely available, and do not reliably detect
the functional abnormalities. Accordingly, by default, functional
gastrointestinal diseases are those involving the abnormal function of
gastrointestinal organs in which abnormalities cannot be seen in the organs with
either the naked eye or the microscope.
Occasionally, diseases that are thought to be functional are ultimately found
to be associated with abnormalities that can be seen. Then, the disease moves
out of the functional category. An example of this is
Helicobacter pylori infection
of the stomach. Many patients with mild upper intestinal symptoms who were
thought to have "functional" abnormal function of the stomach or intestines have been found
to have an infection of the stomach with Helicobacter pylori. This infection can
be diagnosed by seeing the bacterium and the inflammation (gastritis) it causes
under the microscope. When the patients are treated with antibiotics, the
Helicobacter pylori, gastritis, and symptoms disappear. Thus, recognition of
Helicobacter pylori infection removed some patients' diseases from the
The distinction between functional disease and non-functional disease may, in
fact, be blurry. Thus, even functional diseases probably have associated
biochemical or molecular abnormalities that ultimately will be able to be
measured. For example, functional diseases of the stomach and intestines may be
shown ultimately to be caused by reduced levels of normal chemicals within the
gastrointestinal organs, the spinal cord, or the brain. Should a disease that is
demonstrated to be due to a reduced chemical still be considered a functional
disease? I think not. In this theoretical situation, we can't see the
abnormality with the naked eye or the microscope, but we can measure it. If we
can measure an associated or causative abnormality, the disease probably should
no longer be considered functional.
Despite the shortcomings of the term functional, the concept of a functional
abnormality is useful for approaching many of the symptoms originating from the
muscular organs of the gastrointestinal tract. This concept applies particularly
to those symptoms for which there are no associated abnormalities that can be
seen with the naked eye or the microscope.
While IBS is a major functional disease, it is important to mention a second
major functional disease referred to as dyspepsia, or functional dyspepsia. The
symptoms of dyspepsia are thought to originate from the upper gastrointestinal
tract; the esophagus, stomach, and duodenum (the first part of the small
symptoms include upper abdominal discomfort, bloating (the subjective sense of
abdominal fullness without objective distension), or objective distension
(swelling, or enlargement). The symptoms may or may not be related to meals.
There may be nausea with or without
vomiting and early satiety (a sense of
fullness after eating only a small amount of food).
The study of functional disorders of the gastrointestinal tract often is
categorized by the organ of involvement. Thus, there are functional disorders of
the esophagus, stomach, small intestine, colon, and gallbladder. The research on functional disorders
is focused mostly on the esophagus and
stomach (such as dyspepsia), perhaps because these organs are the easiest to reach
and study. Research into functional disorders affecting the small intestine and
colon (for example, IBS) is more difficult to conduct and there is less
agreement among the research studies. This probably is a reflection of the
complexity of the activities of the small intestine and colon and the difficulty
in studying these activities. Functional diseases of the gallbladder, like those
of the small intestine and colon, also are more difficult to study.
Recently, experts in the field of functional gastrointestinal disorders have met to begin organizing an approach to the functional disorders, specifically by setting definitions for the various functional diseases (the Rome I, II, and III criteria). The definition for IBS has been narrowed greatly; as discussed later in this article.
Picture of the organs and glands in the
Reviewed by William C. Shiel Jr., MD, FACP, FACR on 9/18/2012
Is There a Specific Diet for Irritable Bowel
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 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 with lowering pain or decreasing
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 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, although some people report that these
symptoms go away within a few weeks.
Increasing fiber intake by 2 to 3 grams per day will help reduce the risk of
increased gas and bloating.
Drinking six to eight glasses of plain water a day is important, especially
if you have diarrhea. 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 also leads to gas.
Large meals can cause cramping and diarrhea, so eating smaller meals more
often, or eating smaller portions, may help IBS symptoms. Eating meals that 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 may help.
SOURCE: National Digestive Diseases Information Clearinghouse (NDDIC),
National Institutes of Health. Irritable Bowel Syndrome.