Malabsorption occurs when a person's body fails to receive the nutrients it needs from foods that are eaten. It can involve a particular type of nutrient or all nutrients (e.g., fats, carbohydrates, protein, vitamins and minerals).

Malabsorption may result from a disruption of any part of the digestive process within the small intestine. This includes problems with the chemical breakdown of food, absorption of nutrients through the intestinal wall and the transport of nutrients into the bloodstream.

Malabsorption may produce a variety of symptoms based on the type of deficiency present and its cause. For example, problems digesting fats can be caused by poor functioning of the pancreas and lead to steatorrhea (fat buildup in stool). Other symptoms of malnutrition may include diarrhea, anemia and unexplained weight loss, among others.

Diagnosis of malabsorption may include a physical examination and medical history. Certain fecal tests and blood tests can help detect the problem and additional testing may be necessary to determine the cause.

Almost 200 different conditions or diseases are associated with malabsorption. Some of these, such as cystic fibrosis and cancer, cause a number of other problems in addition to malabsorption. Others, such as lactose intolerance and short bowel syndrome, primarily involve malabsorption. Conditions that involve malabsorption may be referred to as malabsorption syndromes.

Treatment and prevention of malabsorption will depend on the type, cause and severity of the condition. Some treatment options include medications, nutritional supplements, and intravenous feeding (total parenteral nutrition).

Malabsorption is the inability of the body to absorb nutrients from food. A number of disorders involve malabsorption. Some are well-defined diseases whereas others are collections of related symptoms. They may all be referred to as malabsorption syndromes.

Normal digestion begins with the chemical breakdown of food in the stomach. These smaller particles of food then pass into the small intestine, where most nutrient absorption occurs. Food particles are further broken down into nutrients such as carbohydrates, fats, protein, vitamins and minerals that can be absorbed through the intestinal walls into the blood. The nutrients are then carried, via the bloodstream, to cells throughout the body for nourishment and energy. Remaining waste travels through the large intestine and exits the body as stool.  

The structure of the small intestine allows for maximum absorption. The many intestinal folds and the projection of villi (fingerlike) and microvilli within the intestinal lining create a large combined surface area. This results in the greatest exposure of nutrients to digestive enzymes.

Malabsorption occurs when any part of the process within the small intestine is interrupted. This may involve impairment in one or more of the following phases of the process:

• Digestion. The chemical breakdown of food particles in the small intestine. The pancreas, bile ducts, liver and gallbladder all play a role in the production of enzymes and bile that help break down food particles into nutrients the body can use. Digestion is regulated by hormones and nerves. Impairment of any of these digestive components can lead to malabsorption.
  

  

• Absorption involving intestinal lining. The mucosal (mucous) lining of the small intestine absorbs and secretes substances during digestion. Problems or abnormalities in the lining of the small intestine can cause malabsorption. Celiac disease is the most common cause of impaired absorption.
  
  
• Transport of nutrients into the bloodstream. The movement of fats and proteins into the bloodstream from the small intestine. When lymph vessels within the small intestine become enlarged or obstructed, nutrients are unable to be carried into the bloodstream for circulation throughout the body. Problems with lymph vessels, such as intestinal lymphangiectasia, may cause this nutrient malabsorption.

Malabsorption may involve the inability to absorb all nutrients (e.g., carbohydrates, fats, protein, vitamins and minerals) or just specific ones.

Malabsorption may occur in:

• Isolated areas of the small intestine due to impaired digestion (e.g., problems absorbing specific nutrients)
  
  
• Throughout the entire small intestine due to conditions that impair absorption abilities (e.g., Celiac disease).  

Untreated, malabsorption can lead to a number of health problems and complications, including malnutrition, vitamin deficiencies, osteoporosis (loss of bone density) and stunted growth or development in children.

The type of malabsorption that occurs is based on the specific nutrient not being absorbed during digestion. Multiple types of malabsorption may occur at the same time. For example, celiac disease and short bowel syndrome are responsible for the malabsorption of fats, protein, carbohydrates, vitamins and minerals.

Types of malabsorption include:

• Fat malabsorption. Inability to absorb fats (found in foods like butter, margarine, oils, meat, fried and processed foods) during digestion. Steatorrhea (fat buildup in stool) is a sign of fat malabsorption. Unexplained weight loss also usually occurs with this type of malabsorption. The inability to absorb fats often occurs in combination with other types of malabsorption and in many conditions that involve malabsorption. The digestion and absorption of fats is a more complex process than that of protein or carbohydrates. This increases the possibility of absorption problems because each step in the process is essential.
  
  
• Carbohydrate malabsorption. Inability to absorb carbohydrates (sugar, starches and fiber found in foods such as bread, potatoes, rice, fruits and vegetables) during digestion. Other carbohydrates include table sugar and lactose, which is commonly found in dairy products. Symptoms of carbohydrate malabsorption include watery, explosive diarrhea, bloating, abdominal distension and flatulence. Lactose intolerance is the most common cause of carbohydrate malabsorption. It may also occur in patients who have undergone extensive bowel resection surgery.
  
  
• Protein malabsorption. Inability to digest and absorb proteins (found in foods such as meat, eggs and beans). Symptoms include swelling that may occur anywhere on the body (edema), dry skin and hair loss. This type of malabsorption may be caused by problems with the pancreas.
  
  
• Vitamin malabsorption. Inability to absorb various vitamins from food as it is being digested. This includes water-soluble vitamins (B and C vitamins) as well as fat-soluble vitamins (vitamins A, D, E and K, which can only be digested and absorbed in conjunction with the processing of fats during digestion). Symptoms of vitamin malabsorption depend on the particular vitamin that is not being absorbed. For example, a B-12 deficiency can cause anemia, fatigue, constipation and weight loss. This can occur as a result of celiac disease or Crohn's disease. Vitamin D deficiency can cause a softening of the bones (osteomalacia), vitamin K deficiency can cause easy bruising and vitamin A deficiency may cause vision problems.
  
  
• Mineral malabsorption. Inability to absorb minerals such as calcium, magnesium, iron, zinc and others. Symptoms and causes may vary, according to the deficient mineral. For example, iron deficiency can result in anemia and may be caused by celiac disease.

Malabsorption can be caused by a wide variety of medical conditions and diseases. Impairments of digestive or absorption processes, or problems with the transport of nutrients into the bloodstream can lead to malabsorption.

The many possible causes of malabsorption can be categorized as being the result of:

• Biochemical/enzyme deficiency. When the body lacks specific chemicals or enzymes necessary for the process of digestion. For example, people with lactose intolerance lack the enzyme lactase, which is necessary to digest lactose, a sugar found in dairy products. Malabsorption can also result when the pancreas is unable to produce the enzymes needed to chemically break down food (e.g., with chronic pancreatitis, cystic fibrosis, diabetes, cancer or resection surgery of the pancreas).
  
  
• Surface area loss. Occurs when a portion of the bowel is surgically removed, reducing the amount of space available for nutrient absorption. This may occur after surgical procedures such as partial bowel resection to remove diseased portions of the intestines. Short bowel syndrome involves malabsorption as the result of surface area loss in the small intestine. Surgery performed for the purpose of weight loss (e.g., bariatric surgery) may also lead to surface area loss and malabsorption.
  
  
• Bacterial overgrowth. When too much bacteria occur in one place. A large number of bacteria in the small intestine may compete for nutrients or may damage the intestinal lining, leading to malabsorption. Bacterial overgrowth is associated with many different disorders, including short bowel syndrome, intestinal obstruction, irritable bowel syndrome and Whipple disease. Prolonged use of medications used to reduce stomach acid, such as proton pump inhibitors or H2 blockers, may also cause malabsorption as a result of bacterial overgrowth.
  
  
• Mucosal (mucous) abnormalities. When disease or abnormalities affect the mucosal lining of the small intestine, its ability to absorb or secrete substances during digestion becomes impaired, causing malabsorption. Celiac disease is a common cause of impaired absorption of the intestinal lining. Crohn's disease, cancer and infection may also cause mucosal abnormalities that can lead to malabsorption.
  
  
• Lymph vessel problems. Inability or reduced ability of nutrients to move from the small intestine into the bloodstream for circulation throughout the body. Malabsorption occurs when lymph vessels that normally carry particular nutrients into the blood become enlarged or obstructed. An example of such a condition is intestinal lymphangiectasia. 

For more information on conditions that involve malabsorption, see Related disorders.

Almost 200 different conditions or diseases are associated with malabsorption. All impair the digestion, absorption or transport of nutrients into the bloodstream from the small intestine. Some of these conditions cause malabsorption in addition to other problems, whereas others primarily involve malabsorption and its complications.  

Conditions that primarily involve malabsorption include:

• Lactose intolerance. An inability to digest dairy products containing lactose due to the lack of the lactase enzyme. As many as 50 million Americans are lactose intolerant, according to the National Institutes of Health (NIH). Related conditions include intolerances to bovine lactalbumin (a protein found in cow’s milk) and soy milk protein, which can also cause malabsorption.
  
  
• Short bowel syndrome. Malabsorption that occurs as the result of lost surface area within the small intestine. This is often caused by conditions such as Crohn's disease or necrotizing enterocolitis (in infants), where diseased sections of the small intestine are removed and subsequently limit nutrient absorption. It may also occur after bariatric surgery, which is performed in an effort to lose weight.
  
  
• Celiac disease. An inherited sensitivity to the protein gluten (found in wheat, barley, rye and oats) that causes damage to the small intestine and interferes with nutrient absorption. It is estimated that approximately 2 million Americans have celiac disease, according to the NIH.
  
  
• Tropical sprue. A disorder caused by an overgrowth of bacteria that results in abnormalities of the small intestine, leading to malabsorption. It typically occurs in people who live or visit tropical or subtropical areas (such as the Caribbean, southern India and Southeast Asia).
  
  
• Whipple disease. This rare, infectious disease injures the lining of the small intestine. Sores and damage to the intestinal wall interfere with the absorption of carbohydrates or fats. Whipple disease may be treated with a prolonged course of antibiotics for up to a year, although relapse is common. If left untreated, it can be fatal.
  
  
• Intestinal lymphangiectasia. A condition in which the lymph nodes in the small intestine become enlarged and obstructed, causing the malabsorption of fats and protein. This condition primarily affects children and young adults.

Other conditions that include malabsorption in addition to other problems include:

• Cystic fibrosis. A hereditary disease that causes the buildup of thick, sticky mucus in the lungs and digestive tract. Mucus may obstruct the pancreas, intestines and bile ducts, as well as the air passages in the lungs. This can result in life-threatening lung infections and serious digestive problems, including malabsorption. According to the Cystic Fibrosis Foundation, the disease affects 30,000 children and adults in the United States.
  
  
• Chronic pancreatitis. Persistent, ongoing inflammation and scarring of the pancreas. It occurs when digestive enzymes attack the pancreas instead of breaking down food in the small intestine. In cases of chronic pancreatitis, the pancreas may eventually stop producing these enzymes, which can lead to malabsorption. Many cases of chronic pancreatitis appear to be caused by alcoholism.
  
  
• Crohn's disease. Inflammation and sores (ulcers) that occur in the lining of the digestive tract. When it occurs in the small intestine, this irritation can limit the small intestine’s ability to absorb nutrients from food. Crohn’s disease may also cause perforation or obstruction of the intestinal wall, which can require surgery. About 500,000 Americans have CD, according to the Crohn's & Colitis Foundation of America.
  
  
• Zollinger-Ellison syndrome. A rare condition in which tumors develop in the pancreas and the small intestine’s duodenum. These tumors stimulate excessive stomach acid, which can damage the lining of the stomach and small intestine, leading to malabsorption.
  
  
• Shwachman-Diamond syndrome. A rare condition that affects the pancreas, bone marrow and skeleton. Failure of the pancreas to produce digestive enzymes in people with this condition can lead to malabsorption.
  
  
• Other conditions. There are many other conditions and diseases that can also cause malabsorption, including:
  
  
• • Infections (e.g., by parasites such as giardia lamblia and hookworm)
    
    
  • Cancers (e.g., lymphoma, pancreatic)
    
    
  • Immune system diseases (e.g., AIDS)

Malabsorption may lead to a variety of signs and symptoms, depending on the type, cause and severity of the malabsorption. Signs and symptoms of malabsorption may include:

• Steatorrhea. Greasy, light-colored stool that is soft, bulky and foul smelling. It may float in water and stick to the side of the toilet bowl, making it difficult to flush away. Steatorrhea is a sign of fat malabsorption. It often occurs in combination with other types of malabsorption and in conditions that involve malabsorption.
  
  
• Diarrhea. Loose, watery stool. Patients with malabsorption may experience chronic diarrhea. Explosive diarrhea may be a sign of carbohydrate malabsorption.
  
  
• Gas. Air produced during digestion that is normally expelled through the anus (flatulence) or mouth (belching). It often occurs in patients with malabsorption due to the fermentation of unabsorbed carbohydrates. Bloating may occur when gas is trapped in the intestines. It may include abdominal distention due to gas and pressure buildup in the intestines. Cramping and abdominal discomfort may occur with bloating and abdominal distension. Bloating and flatulence are often signs of carbohydrate malabsorption.
  
  
• Unexplained weight loss. Patients with malabsorption are not absorbing necessary nutrients which may cause substantial weight loss. This can occur even when patients are consuming a healthy diet.
  
  
• Malnutrition. Poor nourishment. In children, severe cases of malnutrition can lead to stunted growth or development. Signs of malnutrition vary depending on the particular nutrient(s) not being absorbed, but may include:
  
  
• Edema (swelling anywhere in the body)
• Dry skin
• Hair loss
• Anemia
• Easy bruising
• Dehydration
• Fatigue
• Vision problems

Diagnosing malabsorption involves confirming that it is occurring as well as identifying the cause and type. Some patients may not have symptoms or may have symptoms that indicate other conditions. Therefore, tests are necessary for diagnosis.

A physical examination can be used to identify signs of malabsorption or any other condition that may be causing the symptoms. A medical history may include discussion of symptoms, eating habits, alcohol use, current medications, family history of disease and any recent surgeries or foreign travel. In general, patients exhibiting signs of unexplained weight loss, steatorrhea (fat buildup in stool) and anemia may be tested for malabsorption.  

Blood tests will also be performed to determine whether a patient is anemic or lacking in certain nutrients (e.g., low vitamin D may point toward fat malabsorption). These preliminary tests include:

• Complete blood count (CBC). Includes measurement of the number of white and red blood cells. This test is used to identify signs of infection, anemia and various nutrient deficiencies (e.g., vitamin B-12, which is important for digestion).
  
  
• Chem20. Measures the levels of 20 different chemical substances (e.g., protein, glucose, calcium) released from various tissues in the body. Abnormal levels may indicate problems with the tissues that secrete the substance.

Blood tests are typically followed by fecal tests in which stool samples are analyzed in a laboratory. A 72-hour fecal fat measurement requires the collection of a patient’s entire stool output over 72 hours. Then the amount of fat in stool is measured. This is the most reliable test for diagnosing fat malabsorption.

The next test typically performed is the D-xylose absorption test, which assesses whether malabsorption is a problem of absorption (involving the intestinal lining) or digestion (e.g., involving pancreatic insufficiency) within the small intestine. During this test, a patient is given an oral dose of D-xylose (a type of sugar). D-xylose can be absorbed without pancreatic enzymes, but is not used by the body, so it typically exits the body in urine. Urine samples are analyzed for traces of D-xylose.

If D-xylose levels are abnormal, the physician will typically perform an endoscopy. This test allows the physician to view the patient’s digestive tract via a small, flexible tube (with a light and camera) that is inserted through either the mouth or anus. Photos and tissue samples (small bowel biopsy) can be taken during this procedure. Biopsy may identify many different disorders, such as celiac disease, tropical sprue, bacterial overgrowth and inflammatory bowel disease (e.g., Crohn's disease).

If the biopsy is normal, additional tests, such as breath tests, which measure the amount of a particular substance in the breath, may be performed. Common breath tests may include:

• Hydrogen breath test. A test for lactose intolerance. This test measures breath samples for hydrogen after ingestion of a drink that contains high levels of lactose. The body makes excess hydrogen when lactose is not broken down properly in the small intestine. Thus, too much hydrogen in the breath may indicate a failure to absorb lactose.
  
  
• Bile salt breath test. Measures the amount of carbon dioxide in breath after oral administration of bile salt. This measures how well digestion is occurring, and may be able to identify whether malabsorption is the result of liver disease or bacterial overgrowth in the small intestine. This test indicates malabsorption of fats and fat soluble vitamins.
  
  
• Triolein breath test. A test of fat malabsorption. This test measures the level of carbon dioxide in breath after ingestion of a drink containing 14-C triglycerides (a fat-like compound). The test measures a specific type of carbon dioxide that the body normally produces when it digests fats. However, lung disease, thyroid disorders, obesity and other conditions may interfere with test results. The effectiveness of this test in diagnosing malabsorption is not clear.

The Schilling test for B12 malabsorption may also be performed. However, this three-stage urine test that involves the administration of oral and intravenous (into a vein) doses of vitamin B-12 followed by a urine analysis, is becoming increasingly rare.

Other tests that may be used to identify the cause of malabsorption include:

• Barium x-ray. X-rays that are taken after a patient has received a chalky substance (barium) that allows easy viewing of internal organs on x-ray. These x-rays can help identify abnormalities within the digestive tract, such as obstruction, tumors and thickening of the intestinal lining due to inflammation. For an upper gastrointestinal (GI) series, patients drink the barium solution before testing. For a lower GI series, barium is introduced rectally (by enema) prior to testing.
  
  
• Computed axial tomography (CAT). Simultaneous x-rays taken from different angles. A CAT scan allows a physician to analyze the condition of the intestines as well as the pancreas and lymph nodes.
  
  
• Pancreatic function tests. Used to identify abnormalities in the functioning of the pancreas, which can lead to malabsorption. These tests include:
  
  
• • Secretin stimulation test (SST). Test in which a tube is inserted through a patient’s nose into the digestive tract until it reaches the upper portion of the small intestine. Then a hormone called secretin (which normally indicates the presence of food in the small intestine) is released into the area through the tube. Intestinal secretions produced in response to the hormone are removed for examination. This test measures the ability of the pancreas to respond when food particles move into the small intestine from the stomach.
    
    
  • Lundh test. Similar to the SST, except that intestinal secretions are stimulated by a liquid meal containing carbohydrates, proteins and fat. This test is not considered as sensitive as the SST.

Treatment of malabsorption should focus on the underlying cause as well as correcting any existing nutritional deficiencies. Treatment options and prevention methods for patients with malabsorption may differ, based on the type, cause and severity of the condition.

Treatment of malabsorption due to food intolerances may involve simply avoiding those foods a patient is unable to digest. For patients with lactose intolerance, this means avoiding dairy products that contain lactose. Patients with celiac disease should avoid gluten (a protein found in wheat, rye, oats and barley), due to an inability to absorb it. 

Medications may also be used to treat some causes of malabsorption. For example, antibiotics may be used to treat malabsorption caused by infection or bacterial overgrowth in the small intestine. Anti-inflammatory medication may be used to treat patients with malabsorption as a result of Crohn's disease.

Replacing or supplementing nutrients lost during malabsorption may also be necessary. This can include taking supplements or choosing dietary alternatives to replace lost fats, carbohydrates, proteins, vitamins and minerals. For example, a parenteral formula containing medium-chain triglycerides (fats with an unusual chemical structure the body can easily digest) have been used as a fat substitute. In addition, patients with pancreatic insufficiency may wish to take specific supplements (protease and lipase) to make up for the digestive enzymes their pancreas is unable to produce.

In severe cases of malabsorption, intravenous feeding (total parenteral nutrition) may be required. This may be recommended after bowel resection surgery or to avoid aggravating inflamed or damaged intestines.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to malabsorption:

1. How can I tell if I have a problem absorbing nutrients from food?
   
   
2. Based on my symptoms, what type of nutrient (e.g., fat, carbohydrate, protein, vitamin or mineral) do you think my body is unable to digest? What types of food is this nutrient found in?
   
   
3. What do you think is causing my malabsorption?
   
   
4. Should I be screened for any conditions or potential causes? What will this screening involve?
   
   
5. What type of treatment do you recommend for my malabsorption?
   
   
6. Are there specific medications you recommend for me, and what are their side effects?
   
   
7. Do you recommend specific nutritional supplements? Are over-the-counter varieties adequate or will I need a prescription?
   
   
8. For how long will I need to take medication or supplements?
   
   
9. Are there dietary changes you recommend for me? Will this be for a specific length of time or will changes to my diet be continuous and ongoing?
   
   
10. During treatment, are there any side effects or changes that you want me to report to you immediately?