What Causes IBS?
The colon, which is about 6 feet long, connects the small
intestine with the rectum and anus. The major function of the
colon is to absorb water and salts from digestive products that enter from
the small intestine. Two quarts of liquid matter enter the colon
from the small intestine each day. This material may remain there for
several days until most of the fluid and salts are absorbed into
the body. The stool then passes through the colon by a pattern of
movements to the left side of the colon, where it is stored
until a bowel movement occurs.
Colon motility (contraction of intestinal muscles and movement
of its contents) is controlled by nerves and hormones and by electrical
activity in the colon muscle. The electrical activity serves as a
“pacemaker” similar to the mechanism that controls heart
Movements of the colon propel the contents slowly back and forth
but mainly toward the rectum. A few times each day strong muscle
contractions move down the colon pushing fecal material ahead of
them. Some of these strong contractions result in a bowel
Because doctors have been unable to find an organic cause, IBS
often has been thought to be caused by emotional conflict or stress.
While stress may worsen IBS symptoms, research suggests that other
factors also are important. Researchers have found that the colon
muscle of a person with IBS begins to spasm after only mild
stimulation. The person with IBS seems to have a colon that is
more sensitive and reactive than usual, so it responds strongly to
stimuli that would not bother most people.
Ordinary events such as eating and distention from gas or other
material in the colon can cause the colon to overreact in the
IBS. Certain medicines and foods may trigger spasms in some
people. Sometimes the spasm delays the passage of stool, leading
to constipation. Chocolate, milk products, or large amounts of alcohol are frequent offenders. Caffeine causes loose stools in many people, but it is more likely to affect those with IBS. Researchers also
have found that women with IBS may have more symptoms during their
menstrual periods, suggesting that reproductive hormones can
increase IBS symptoms.
Researchers have determined that IBS patients have elevated food-specific IgG4 antibodies to common foods such as wheat, beef, pork, lamb, and soya bean. These findings are published in the July 2005 issue of The American Journal of Gastroenterology.
What Are the Symptoms of IBS?
If you are concerned about IBS, it is important to realize that
normal bowel function varies from person to person. Normal bowel
movements range from as many as three stools a day to as few as
three a week. A normal movement is one that is formed but not
hard, contains no blood, and is passed without cramps or pain.
People with IBS, on the other hand, usually have crampy
abdominal pain with painful constipation or diarrhea. In some
people, constipation and diarrhea alternate. Sometimes people with IBS
pass mucus with their bowel movements. Bleeding, fever, weight loss,
and persistent severe pain are not symptoms of IBS but may
indicate other problems.
How Is IBS Diagnosed?
IBS usually is diagnosed after doctors exclude the presence of
disease. To get to that point, the doctor will take a complete
medical history that includes a careful description of symptoms. A physical
examination and laboratory tests will be done. A stool sample
will be tested for evidence of bleeding. The doctor also may do diagnostic procedures such as x-rays or endoscopy (viewing the colon through a flexible tube inserted through the anus) to find out if there is disease.