CASE FILES: BIOCHEMISTRY
A N SW E R S TO CASE 25: IRRITABLE BO W EL SYNDR O M E
A 38-year-old female complains of alternating constipation and
diarrhea associated with times of stress and abdominal cramping and bloating
relieved with bowel movements. She is prescribed a cellulose dietary
Diagnosis: Irritable bowel syndrome.
Biochemical mechanism: Cellulose-containing foods are not digestible
but swell up by absorbing water and correlate with larger softer stools.
The increase in dietary fiber also increases the intestinal transit time and
decreases the intracolic pressure, thereby decreasing the symptoms of
C L IN IC A L C O R R E L A T IO N
Irritable bowel syndrome affects many individuals in Western countries, and it
manifests as abdominal cramping and bloating in the absence of disease. It is
thought to be caused by increased spasms of the intestines. Constipation with
or without episodes of diarrhea may be seen. Weight loss, fever, vomiting,
bloody stools, or anemia would be worrisome and should not be attributed to
irritable bowel syndrome. Typically, affected patients are anxious and may be
under stress. After ruling out other disease processes, a trial of fiber-containing
foods, stress reduction, and avoidance of aggravating foods are effective ther-
apies. Patients should be advised to avoid laxative use. Rarely antispasmodic
or antiperistaltic agents can be used. Notably, increased fiber in the diet may
also decrease the absorption of fats and may lower the risk of colon cancer.
A PPR O A C H TO IN D IG E ST IB L E PO L Y SA C C H A R ID E S
Know about the indigestible polysaccharides.
Be aware of P-1,4 cellulose bonds.
Know about the major types of fiber.
Cellulose: A polysaccharide composed of P-
-glucopyranose units joined
by a P(1—>4) glycosidic bond, which is not hydrolyzed by enzymes in
the digestive tracts of humans.
Gums: Complex polysaccharides composed of arabinose, fucose, galac-
tose, mannose, rhamnose, and xylose. Gums are soluble in water and,
because of their mucilaginous nature, slowly digestible.