Your small intestine does most of the digesting of the foods you eat. If you have a malabsorption syndrome, your small intestine cannot absorb nutrients from foods.

Causes of malabsorption syndromes include

• Celiac disease
• Lactose intolerance
• Short bowel syndrome. This happens after surgery to remove half or more of the small intestine. You might need the surgery if you have a problem with the small intestine from a disease, injury, or birth defect.
• Whipple disease, a rare bacterial infection
• Genetic diseases
• Certain medicines

Symptoms of different malabsorption syndromes can vary. They often include chronic diarrhea, abnormal stools, weight loss, and gas. Your doctor may use lab, imaging, or other tests to make a diagnosis.

Treatment of malabsorption syndromes depends on the cause.

Celiac disease is an immune disease in which people can't eat gluten because it will damage their small intestine. If you have celiac disease and eat foods with gluten, your immune system responds by damaging the small intestine. Gluten is a protein found in wheat, rye, and barley. It may also be in other products like vitamins and supplements, hair and skin products, toothpastes, and lip balm.

Celiac disease affects each person differently. Symptoms may occur in the digestive system, or in other parts of the body. One person might have diarrhea and abdominal pain, while another person may be irritable or depressed. Irritability is one of the most common symptoms in children. Some people have no symptoms.

Celiac disease is genetic. Blood tests can help your doctor diagnose the disease. Your doctor may also need to examine a small piece of tissue from your small intestine. Treatment is a diet free of gluten.

Celiac disease is a condition in which the immune system is abnormally sensitive to gluten, a protein found in wheat, rye, and barley. Celiac disease is an autoimmune disorder; autoimmune disorders occur when the immune system malfunctions and attacks the body's own tissues and organs. Without a strict, lifelong gluten-free diet, inflammation resulting from immune system overactivity may cause a wide variety of signs and symptoms involving many parts of the body.

Celiac disease can develop at any age after an individual starts eating foods containing gluten. The classic symptoms of the condition result from inflammation affecting the gastrointestinal tract. This inflammation damages the villi, which are small, finger-like projections that line the small intestine and provide a greatly increased surface area to absorb nutrients. In celiac disease, the villi become shortened and eventually flatten out. Intestinal damage causes diarrhea and poor absorption of nutrients, which may lead to weight loss. Abdominal pain, swelling (distention), and food intolerances are common in celiac disease. Inflammation associated with celiac disease may lead to an increased risk of developing certain gastrointestinal cancers such as cancers of the small intestine or esophagus.

Inflammation and poor nutrient absorption may lead to problems affecting many other organs and systems of the body in affected individuals. These health problems may include iron deficiency that results in a low number of red blood cells (anemia), vitamin deficiencies, low bone mineral density (osteoporosis), itchy skin rashes (dermatitis herpetiformis), defects in the enamel of the teeth, chronic fatigue, joint pain, poor growth, delayed puberty, infertility, or repeated miscarriages. Neurological problems have also been associated with celiac disease; these include migraine headaches, depression, attention-deficit/hyperactivity disorder (ADHD), and recurrent seizures (epilepsy). Many people with celiac disease have one or more of these varied health problems but do not have gastrointestinal symptoms. This form of the condition is called nonclassic celiac disease. Researchers now believe that nonclassic celiac disease is actually more common than the classic form.

Celiac disease often goes undiagnosed because many of its signs and symptoms are nonspecific, which means they may occur in many disorders. Most people who have one or more of these nonspecific health problems do not have celiac disease. On average, a diagnosis of celiac disease is not made until 6 to 10 years after symptoms begin.

Some people have silent celiac disease, in which they have no symptoms of the disorder. However, people with silent celiac disease do have immune proteins in their blood (antibodies) that are common in celiac disease. They also have inflammatory damage to their small intestine that can be detected with a biopsy.

In a small number of cases, celiac disease does not improve with a gluten-free diet and progresses to a condition called refractory sprue. Refractory sprue is characterized by chronic inflammation of the gastrointestinal tract, poor absorption of nutrients, and an increased risk of developing a type of cancer of the immune cells called T-cell lymphoma.

Gluten is a protein found in wheat, rye, and barley. It is found mainly in foods but may also be in other products like medicines, vitamins, and supplements. People with gluten sensitivity have problems with gluten. It is different from celiac disease, an immune disease in which people can't eat gluten because it will damage their small intestine.

Some of the symptoms of gluten sensitivity are similar to celiac disease. They include tiredness and stomachaches. It can cause other symptoms too, including muscle cramps and leg numbness. But it does not damage the small intestine like celiac disease.

Researchers are still learning more about gluten sensitivity. If your health care provider thinks you have it, he or she may suggest that you stop eating gluten to see if your symptoms go away. However, you should first be tested to rule out celiac disease.

Many people who have celiac disease have not been diagnosed. However, experts estimate about 2 million people in the United States have celiac disease and about 1 percent of people around the world have celiac disease.

Experts have found that some people have both celiac disease and other disorders related to the immune system. These disorders include

• type 1 diabetes
• thyroid diseases, such as Hashimoto’s disease, Graves’ disease, Addison’s disease, and primary hyperparathyroidism
• selective immunoglobulin A (IgA) deficiency, a condition in which your body makes little or no IgA, an antibody that fights infections
• rheumatic diseases, such as Sjögren’s syndrome
• liver diseases, such as autoimmune hepatitis, primary sclerosing cholangitis, and primary biliary cholangitis

Lactose intolerance is a condition that makes it difficult to digest lactose, a sugar found in milk and several other dairy products. Lactose is normally broken down by an enzyme called lactase, which is produced by cells in the lining of the small intestine. Lack or loss of lactase has both genetic and non-genetic causes.

Congenital lactase deficiency, also called congenital alactasia, is a disorder in which infants are unable to break down the lactose in breast milk or formula. This form of lactose intolerance results in very severe diarrhea. If affected infants are not given a lactose-free infant formula, they may experience severe dehydration and weight loss.

Lactose intolerance in adulthood can be caused by the reduced production of lactase after infancy (lactase nonpersistence). If individuals with lactose intolerance consume lactose-containing dairy products, they may experience abdominal pain, bloating, flatulence, nausea, and diarrhea beginning 30 minutes to 2 hours later.

Most people with lactase nonpersistence retain some lactase activity and can include varying amounts of lactose in their diets without experiencing symptoms. Often, affected individuals have difficulty digesting fresh milk but can eat certain dairy products such as cheese or yogurt without discomfort. These foods are made using fermentation processes that break down much of the lactose in milk.

Your small intestine is the longest part of your digestive system - about twenty feet long! It connects your stomach to your large intestine (or colon) and folds many times to fit inside your abdomen. Your small intestine does most of the digesting of the foods you eat. It has three areas called the duodenum, the ileum, and the jejunum.

Problems with the small intestine can include:

• Bleeding
• Celiac disease
• Crohn's disease
• Infections
• Intestinal cancer
• Intestinal obstruction
• Irritable bowel syndrome
• Ulcers, such as peptic ulcer

Treatment of disorders of the small intestine depends on the cause.

Short bowel syndrome is a group of problems related to poor absorption of nutrients. Short bowel syndrome typically occurs in people who have

• had at least half of their small intestine removed and sometimes all or part of their large intestine removed
• significant damage of the small intestine
• poor motility, or movement, inside the intestines

Short bowel syndrome may be mild, moderate, or severe, depending on how well the small intestine is working.

People with short bowel syndrome cannot absorb enough water, vitamins, minerals, protein, fat, calories, and other nutrients from food. What nutrients the small intestine has trouble absorbing depends on which section of the small intestine has been damaged or removed.

What is Whipple's disease?

Whipple's disease is a multi-system infectious bacterial disease that interferes with the body's ability to metabolize fats. Caused by the bacterium Tropheryma whipplei, the disorder can affect any system in the body, including the brain, eyes, heart, joints, and lungs, but usually occurs in the gastrointestinal system. Neurological symptoms occur in up to 40 percent of individuals and may include dementia, abnormalities of eye and facial muscle movements, headaches, seizures, loss of muscle control, memory loss, weakness, and vision problems. Gastrointestinal symptoms may include diarrhea, weight loss, fatigue, weakness, and abdominal bleeding and pain. Fever, cough, anemia, heart and lung damage, darkening of the skin, and joint soreness may also be present. The disease is more common in men and neurological symptoms are more common in individuals who have severe abdominal disease. Rarely, neurological symptoms may appear without gastrointestinal symptoms and can mimic symptoms of almost any neurologic disease.

Is there any treatment?

The standard treatment for Whipple's disease is a prolonged course of antibiotics (up to two years), including penicillin and cefriaxone or doxycycline with hydroxychloroquine. Sulfa drugs (sulfonamides) such as sulfadizine or solfamethoxazole can treat neurological symptoms. Relapsing neurologic Whipple's disease (marked by bouts of worsening of symptoms) is sometimes treated with a combination of antibiotics and weekly injections of interferon gamma, a substance made by the body that activates the immune system.

What is the prognosis?

Generally, long-term antibiotic treatment to destroy the bacteria can relieve symptoms and cure the disease. If left untreated, the disease is progressive and fatal. Individuals with involvement of the central nervous system generally have a worse prognosis and may be left with permanent neurologic disability. Deficits may persist and relapses may still occur in individuals who receive appropriate treatment in a timely fashion. Prognosis may improve with earlier recognition, diagnosis, and treatment of the disorder.