Maldigestion and Malabsorption Syndromes: Overview

Maldigestion and malabsorption syndromes are conditions that result in abnormalities in the digestion of food or in the intestinal absorption of nutrients into the bloodstream. These conditions often occur together.

What Are Maldigestion and Malabsorption Syndromes?

In order for the body to use food, it must be chemically broken down into smaller compounds and then absorbed from the intestine into the bloodstream. If maldigestion occurs, the food a person eats is not broken down enough for the intestine to absorb it. If malabsorption occurs, the food is correctly digested, but abnormalities in the intestine prevent its absorption. As a result, the body does not get all the nutrients it needs; undigested or unabsorbed nutrients are lost in feces * . Maldigestion and malabsorption can occur with proteins, fats, carbohydrates (sugars and starches), and any of the vitamins or minerals the body needs. Often more than one type of nutrient is affected.

What Causes Maldigestion and Malabsorption Syndromes?

Many different diseases can cause malabsorption of various nutrients. The most common disease causing malabsorption is celiac disease, also called celiac sprue or gluten-sensitive enteropathy. As many as 1 in 141 Americans has celiac disease, although most remain undiagnosed. Celiac disease affects children and adults in all parts of the world and is more common in Caucasians and females. People with celiac disease cannot tolerate gluten, a protein found in wheat, rye, and barley. When people with celiac disease eat food containing gluten, their immune system * responds by causing the cells lining the wall of the small intestine to become inflamed. Over time, the inflammation * damages these cells so that they can no longer absorb a normal amount of nutrients.

Lactose intolerance usually can be managed by following simple strategies:

Lactose intolerance refers to the inability of the small intestine to break down the sugar lactose (LAK-tos) due to a lack or too little of the enzyme lactase (LAK-tays). Lactose is a complex sugar found in milk products. Normally, when lactose reaches the small intestine, it is broken down into the simple sugars glucose (GLOO-kos) and galactose (ga-LAK-tos) by a protein, or enzyme, called lactase. Simple sugars can be absorbed easily through the wall of the small intestine into the bloodstream, but larger, more complex sugars such as lactose cannot. If someone is lactose intolerant, that person's intestine does not make enough lactase or the lactase it does make does not work properly.

If lactose is not broken down, it absorbs water, so that the water cannot pass through the intestinal wall into the bloodstream. This extra fluid remaining in the bowel causes diarrhea. Bacteria (microorganisms) in the colon convert lactose to lactic (LAK-tik) acid in a process called fermentation (fur-men-TAY-shun). This fermentation can cause bowel movements to be acidic and burn, and it also causes gas, bloating, and cramps. Lactose intolerance is not dangerous, but it is uncomfortable.

Lactose intolerance is not the same as cow's milk intolerance, and in fact they are not related. Lactose intolerance is a condition associated with the digestive system. Intolerance to cow's milk is actually an allergic reaction, and it is associated with the immune system.

There are three major types of lactose intolerance:

  1. Primary lactose intolerance is a normal consequence of development and aging. The amount of lactase falls as an individual ages. The capacity to digest lactose varies among people, especially as they get older.
  2. Secondary lactose intolerance is associated with damage to the small intestine and loss of the lactase contained within the cells. Diseases such as Crohn's disease or celiac disease may result in lactose intolerance.
  3. Developmental lactose intolerance is congenital in nature. Babies who have a lactase deficiency present at birth are usually diagnosed as having lactose intolerance during early infancy.

The symptoms of lactose intolerance vary from person to person and depend on the amount of lactose eaten. Trial and error helps people learn what not to eat or how much they can eat without becoming ill. Avoiding or severely limiting milk products should eliminate symptoms of lactose intolerance, but people on such a diet must get calcium and vitamin D from other sources. Nonprescription products containing lactase are available that can be taken along with milk products and help the body break down lactose.

The second most common cause of maldigestion and malabsorption is cystic fibrosis. This complex inherited disease involves the lungs, pancreas * , liver, and intestines. One aspect of the disease is that the pancreas does not produce enough digestive enzymes * (a problem of maldigestion), and abnormal chemistry of the intestines prevents normal absorption of nutrients.

Lactose maldigestion is a condition in which the cells lining the small intestine do not produce the enzyme lactase that is needed to digest the sugar lactose found in cow's milk. According to the National Institute of Diabetes and Digestive and Kidney Diseases, between 30 and 50 million American adults are lactose intolerant; these people may produce some lactase and can consume small amounts of dairy products, but they do not produce enough of the enzyme to digest the quantity of dairy products found in the standard American diet.

Other conditions and diseases that cause malabsorption include short bowel syndrome, Crohn's disease, and some weight control surgeries (bariatric surgeries) that shorten the intestine. AIDS * can also cause malabsorption of nutrients, as can diseases of the pancreas, including pancreatitis and pancreatic cancer. Infection with certain intestinal parasites * can interfere with the absorption of food. Certain drugs may also interfere with absorption of specific nutrients for as long as the drug is taken. Absorption normally improves after the drug is stopped.

What Are the Symptoms of Maldigestion and Malabsorption Syndromes?

Regardless of the cause, malabsorption and maldigestion syndromes produce somewhat similar symptoms. The most common symptoms are a bloated abdomen (stomach); chronic * diarrhea; passing a great deal of gas; bulky, bad-smelling stools; excessive fat in the stool (a condition called steatorrhea; stool often floats in the toilet because fat is lighter than water); weight loss; anemia * ; general weakness; fatigue; and fluid retention. Infants and young children gain little weight and do not reach developmental milestones at the times expected, a condition called failure to thrive.

How Are Maldigestion and Malabsorption Syndromes Diagnosed and Treated?

* , and various electrolytes. Imaging studies such as an endoscopy * may be performed to observe the appearance of the small intestine and to biopsy * the innermost surface, called the mucosa. Specific diagnostic tests are performed for fat, protein, and carbohydrate malabsorption as well as for malabsorption of certain vitamins and minerals. Because many malabsorption syndromes are caused by other diseases, the issue is often not one of diagnosis, but rather of measuring the degree of nutrient deficiency and attempting to correct it.

Treatment depends on the cause of the syndrome. Eliminating gluten from the diet helps people with celiac disease. Limiting or eliminating dairy products helps people who are lactose intolerant. Some low-lactose and lactose-reduced products are available in the supermarket. Lactase, the enzyme that breaks down lactose so that it can be absorbed, can be eaten as a digestive aid. People with cystic fibrosis * are given supplemental pancreatic enzymes to aid digestion. Based on the specific nutrient deficiencies, people with malabsorption syndrome are given supplements of various vitamins and minerals, and the amount of calories in their diet may be increased. Malabsorption syndromes usually require life-long dietary adjustments and monitoring. Complications frequently arise based on deficiencies in specific vitamins and minerals.

See also Celiac Disease • Cystic Fibrosis


Books and Articles

Bower, Sylvia Llewelyn, and Mary Kay Sharrett. Celiac Disease: A Guide to Living with Gluten Intolerance. 2nd ed. New York: Demos Health, 2014.

Thompson, Helen. “An Evolutionary Whodunit: How Did Humans Develop Lactose Tolerance?” NPR. December 28, 2012. (accessed April 7, 2016).


MedlinePlus. “Lactose Intolerance.” U.S. National Library of Medicine, National Institutes of Health. (accessed April 7, 2016).

Merck Manual: Consumer Version. “Malabsorption.” (accessed April 7, 2016).

National Institute of Diabetes and Digestive and Kidney Diseases. “Celiac Disease.” (accessed April 7, 2016).


Celiac Disease Foundation. 20350 Ventura Blvd., Suite 240, Woodland Hills, CA 91364. Telephone: 818-716-1513. Website: (accessed April 7, 2016).

Cystic Fibrosis Foundation. 6931 Arlington Rd., 2nd Floor, Bethesda, MD 20814. Telephone: 301-951-4422. Website: (accessed April 7, 2016).

National Institute of Diabetes and Digestive and Kidney Diseases. 2 Information Way, Bethesda, MD 20892. Telephone: 301-496-3583. Website: (accessed April 7, 2016).

* feces (FEE-seez) is the excreted waste from the gastrointestinal tract.

* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.

* inflammation (in-fla-MAY-shun) is the body's reaction to irritation, infection, or injury that often involves swelling, pain, redness, and warmth.

* pancreas (PAN-kree-us) is the gland located behind the stomach that produces enzymes and hormones necessary for digestion and metabolism.

* enzymes (EN-zimes) are proteins that help speed up a chemical reaction in a cell or organism.

* AIDS (or Acquired Immunodeficiency [ih-myoo-no-dih-FIH-shen-see] Syndrome) is an infection that severely weakens the immune system; it is caused by the human immunodeficiency virus (HIV).

* parasites (PAIR-uh-sites) are organisms such as a protozoa (one-celled animals), worms, or insects that must live on or inside a human or other organism to survive. An animal or plant harboring a parasite is called its host. Parasites live at the expense of the host and may cause illness. The adjectival form is parasitic.

* chronic (KRAH-nik) means lasting a long time or recurring frequently.

* anemia (uh-NEE-me-uh) is a blood condition in which there is a decreased hemoglobin in the blood and, usually, fewer than normal numbers of red blood cells.

* triglycerides (try-GLISS-eh-rides) are a type of fatty substances found in the blood.

* endoscopy (en-DOS-ko-pee) is a type of diagnostic test in which a lighted tube-like instrument is inserted into a part of the body.

* biopsy (BI-op-see) is a test in which a small sample of skin or other body tissue is removed and examined for signs of disease.

* cystic fibrosis (SIS-tik fy-BRO-sis) is a disease that causes the body to produce thick mucus that clogs passages in many of the body's organs, including the lungs.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)