Certain disorders, infections, and surgical procedures can cause malabsorption.
Malabsorption causes diarrhea, weight loss, and bulky, foul-smelling stools.
The diagnosis is based on typical symptoms along with stool tests and sometimes a biopsy of the lining of the small intestine.
The treatment depends on the cause.
Causes of Malabsorption
Normally, foods are digested and nutrients (proteins, carbohydrates, fats, vitamins, and minerals) are absorbed into the bloodstream mainly in the small intestine.
Malabsorption may occur if a disorder
Interferes with the digestion of food
Interferes with the absorption of nutrients
Digestion problems
Digestion of food can be affected by
Disorders that prevent adequate mixing of food with digestive enzymes and stomach acid
Insufficient production of digestive enzymes
Decreased production of bile
Too much stomach acid
Too little stomach acid (atrophic gastritis Causes
)The wrong kinds of bacteria growing in the small intestine
Inadequate mixing may occur in a person who has had part of the stomach surgically removed.
In some disorders, the body produces inadequate amounts or types of digestive enzymes, which are necessary for the breakdown of food. For example, a common cause of malabsorption is insufficient production of digestive enzymes by the pancreas, which occurs with some pancreatic diseases, or by the small intestine, which occurs in lactase deficiency Lactose Intolerance Lactose intolerance is the inability to digest the sugar lactose because of a lack of the digestive enzyme lactase, leading to diarrhea and abdominal cramping. Lactose intolerance is caused... read more .
Decreased production of bile, too much or too little acid in the stomach, or too many of the wrong kinds of bacteria growing in the small intestine (see Small Intestinal Bacterial Overgrowth Small Intestinal Bacterial Overgrowth (SIBO) Small intestinal bacterial overgrowth is a disorder in which poor movement of intestinal contents allows certain normal intestinal bacteria to grow excessively, causing diarrhea and poor absorption... read more ) may also interfere with digestion.
Absorption problems
Absorption of nutrients into the bloodstream can be affected by
Disorders that injure the lining of the small intestine
Surgical removal of a large section of the small intestine
Disorders that affect the flow of lymphatic fluid from the bowel
The normal lining consists of small projections called villi and even smaller projections called microvilli, which create an enormous surface area for absorption. Infections Overview of Gastroenteritis Gastroenteritis is inflammation of the lining of the stomach and small and large intestines. It is usually caused by infection with a microorganism but can also be caused by ingestion of chemical... read more 
(bacterial, viral, or parasitic) and disorders such as celiac disease Celiac Disease Celiac disease is a hereditary intolerance to gluten (a protein found in wheat, barley, and rye) that causes characteristic changes in the lining of the small intestine, resulting in malabsorption... read more 
and Crohn disease Crohn Disease Crohn disease is an inflammatory bowel disease where chronic inflammation typically involves the lower part of the small intestine, the large intestine, or both and may affect any part of the... read more 
all may injure the intestinal lining.
Surgical removal of a large section of the small intestine substantially reduces the surface area for absorption (see Short Bowel Syndrome Short Bowel Syndrome Short bowel syndrome is a disorder causing diarrhea and poor absorption of nutrients ( malabsorption), which often occurs after surgical removal of a large portion of the small intestine. This... read more ).
Disorders that affect the flow of lymphatic fluid from the bowel into the bloodstream (the path that fats must take to enter the bloodstream), such as malformation of intestinal lymph vessels (see Intestinal Lymphangiectasia Intestinal Lymphangiectasia Intestinal lymphangiectasia is a rare disorder in which the lymph vessels supplying the lining of the small intestine are blocked, resulting in malabsorption. This disorder is the result of... read more ), blockage of lymph vessels due to lymphoma (cancer of the lymphatic system), or impaired entry of lymph fluid into the bloodstream due to some heart disorders, also reduce absorption.
Symptoms of Malabsorption
Symptoms of malabsorption are caused by the increased passage of unabsorbed nutrients through the digestive tract or by the nutritional deficiencies that result from inadequate absorption.
The most common symptom of malabsorption is
Chronic diarrhea
When there is inadequate absorption of fats in the digestive tract, stool contains excess fat and is light-colored, soft, bulky, greasy, and unusually foul-smelling (such stool is called steatorrhea). The stool may float or stick to the side of the toilet bowl and may be difficult to flush away. The inadequate absorption of certain sugars can cause explosive diarrhea, abdominal bloating, and flatulence.
Malabsorption can cause deficiencies of all nutrients or selective deficiencies of proteins, fats, sugars, vitamins, or minerals. People with malabsorption usually lose weight or have difficulty maintaining their weight despite adequate consumption of food. Women may stop menstruating.
The symptoms vary depending on the specific deficiencies. For example, a protein deficiency can cause swelling and accumulation of fluid (edema) anywhere throughout the body, dry skin, and hair loss. Anemia Overview of Anemia Anemia is a condition in which the number of red blood cells is low. Red blood cells contain hemoglobin, a protein that enables them to carry oxygen from the lungs and deliver it to all parts... read more (caused by vitamin or iron deficiency) may cause fatigue and weakness.
Diagnosis of Malabsorption
A doctor's evaluation of the person's history and symptoms
Tests to confirm the diagnosis (such as blood and stool tests)
Tests to diagnose the cause (such as biopsy and imaging)
A doctor suspects malabsorption when a person has chronic diarrhea, weight loss, anemia, and other signs of nutritional deficiencies. Malabsorption is less obvious and often more difficult to recognize in older people than in children.
Laboratory tests can help confirm the diagnosis:
Tests to measure fat in stool
Visual examination of stool
Blood tests
A stool test that directly measures the amount of fat in stool that has been collected over 3 days is the most reliable one for diagnosing malabsorption of fat, which is present in almost all malabsorption disorders. A finding of more than 7 grams of fat in the stool daily is the hallmark of malabsorption. Also available are a few other tests that measure fat in the stool but do not require the 3-day collection of stool.
Stool samples are examined with the unaided eye as well as under the microscope. Undigested food fragments may mean that food passes through the intestine too rapidly. In a person with jaundice, stool with excess fat indicates decreased production or secretion of bile. Sometimes parasites or their eggs are seen under the microscope, suggesting that malabsorption is caused by a parasitic infection.
Blood tests and other laboratory tests can be done to detect malabsorption of other specific substances, such as lactose or vitamin B12.
Once a doctor confirms a person has a malabsorption disorder, tests are done to diagnose the cause:
Biopsy
Imaging tests
Pancreatic function tests
A biopsy may be needed to detect abnormalities in the lining of the small intestine. The tissue is removed through an endoscope (a flexible viewing tube equipped with a light source and a camera through which a small clipper can be inserted) passed through the mouth and into the small intestine.
Imaging tests, such as video capsule endoscopy Video Capsule Endoscopy Video capsule endoscopy (wireless video endoscopy) is a procedure in which the person swallows a battery-powered capsule. The capsule contains one or two small cameras, a light, and a transmitter... read more , computed tomography Computed Tomography and Magnetic Resonance Imaging of the Digestive Tract Computed tomography (CT) and magnetic resonance imaging (MRI) scans are good tests for assessing the size and location of abdominal organs. Additionally, cancerous (malignant) or noncancerous... read more , or barium x-rays Barium X-Ray Studies of the Digestive Tract X-rays often are used to evaluate digestive problems. Standard x-rays ( plain x-rays) can show some blockages or paralysis of the digestive tract, or abnormal air patterns in the abdominal cavity... read more may be done.
Pancreatic function tests are done if the doctor thinks that the cause of malabsorption may be the insufficient production of digestive enzymes by the pancreas. However, some of these tests are complex, time-consuming, and invasive. In one test, a tube is passed through the mouth and guided into the small intestine, where intestinal fluids containing pancreatic secretions can be collected and measured. In another test, the person swallows a substance that requires pancreatic enzymes for its digestion. The products of digestion are then measured in the urine. Recently, doctors have been doing simpler and easier tests that measure levels of certain pancreatic enzymes in the stool.
Other diagnostic tests (including culture of digestive bacteria, certain blood tests, or breath tests) may also be done.
