Intestinal Malabsorption

How absorption normally works

Digestion breaks food into small pieces that the lining of the small intestine can absorb. This depends on three steps:

1. Breakdown in the gut cavity: pancreatic enzymes digest fat, protein and starch, and bile from the liver emulsifies fat.
2. Absorption by the lining: finger-like villi with a huge surface area take nutrients into the cells. Enzymes on their surface, such as lactase, finish digesting sugars.
3. Transport away: nutrients pass into blood and lymph vessels.

Malabsorption can result from a fault at any step. Different nutrients are absorbed at different places: iron and calcium in the first part of the small intestine (duodenum), most nutrients in the middle (jejunum), and vitamin B12 and bile acids at the end (terminal ileum). That is why the pattern of deficiencies can point to where the problem is.

Symptoms of malabsorption

Gut symptoms

• Diarrhea lasting weeks or months
• Steatorrhea: pale, bulky, greasy, very smelly stools that float or leave an oily film and are hard to flush
• Bloating, rumbling and excess gas, especially when sugars are not absorbed
• Cramping abdominal discomfort

Symptoms of nutrient deficiency

Some people, especially with mild celiac disease, have no gut symptoms and are diagnosed only because of unexplained anemia or bone thinning.

Causes of intestinal malabsorption

Damage to the intestinal lining

• Celiac disease: an immune reaction to gluten flattens the villi. It is one of the commonest causes and affects about 1 in 100 people.
• Crohn's disease: inflammation, especially of the ileum, impairs B12 and bile acid absorption.
• Infections: giardia and other parasites, Whipple disease (rare), HIV-related infections, and tropical sprue after time in the tropics.
• Radiation enteritis after pelvic or abdominal radiotherapy.
• Medicines: some drugs, such as olmesartan, can damage the lining; others like orlistat block fat absorption on purpose.

Enzyme deficiencies

• Lactose intolerance: low lactase means milk sugar is not absorbed and ferments in the colon, causing gas, bloating and diarrhea after dairy.
• Other sugar intolerances: fructose, sucrase-isomaltase deficiency (rare, genetic).

Problems with digestion before absorption

• Pancreatic insufficiency: too few digestive enzymes, from chronic pancreatitis, cystic fibrosis, pancreatic cancer or pancreatic surgery. Fatty stools are prominent.
• Bile problems: blocked bile ducts or liver disease reduce fat digestion; stools may be pale and urine dark.

Structural and surgical causes

• Short bowel syndrome: after removal of a large length of small intestine.
• Bariatric surgery and stomach surgery.
• Small intestinal bacterial overgrowth (SIBO): too many bacteria in the small intestine compete for nutrients and break down bile. It is more likely with diabetes, slow gut movement, previous surgery or long-term acid-suppressing medicines.

Other causes

• Lymphatic blockage (intestinal lymphangiectasia)
• Thyroid disease, diabetes and some hormone-secreting tumors that speed up the gut
• Amyloidosis and immune deficiencies

Diagnosis

Your doctor will ask about your stools, weight change, diet, travel, surgery, alcohol use and family history, and examine for weight loss, pallor, swelling and abdominal tenderness. Tests are chosen to answer two questions: is there malabsorption, and what is causing it?

Blood tests

• complete blood count for anemia
• iron studies, B12, folate, vitamin D, calcium, magnesium, albumin
• clotting time (INR) as a marker of vitamin K
• celiac antibody test (tTG-IgA), taken while you are still eating gluten
• inflammatory markers, thyroid function

Stool tests

• Fecal elastase: low in pancreatic insufficiency
• Stool fat: confirms steatorrhea
• infection tests for giardia and other parasites
• Fecal calprotectin: raised with bowel inflammation such as Crohn's disease

Breath tests

Hydrogen and methane breath tests after drinking a sugar solution help diagnose lactose intolerance and bacterial overgrowth.

Endoscopy and imaging

• Upper endoscopy with small intestine biopsies: confirms celiac disease and shows other lining diseases.
• Colonoscopy with ileal biopsies for Crohn's disease.
• CT or MRI of the abdomen or pancreas, and capsule endoscopy in selected cases.

Treatment

Treat the cause

Replace nutrients

• Vitamin and mineral supplements based on blood results. B12 may need injections if absorption in the ileum is impaired.
• Extra calories and protein; a dietitian can tailor the plan.
• Fat-soluble vitamins (A, D, E, K) in special water-miscible forms when fat absorption is poor.
• Medium-chain triglyceride (MCT) oils, which are absorbed without bile or lymph, for some conditions.

Ease symptoms

• Drink enough fluids and use oral rehydration solutions during flare-ups.
• Anti-diarrheal medicines may be used once infection is excluded and on medical advice.

Complications

Untreated malabsorption can lead to anemia, osteoporosis and fractures, poor growth and delayed puberty in children, infertility, kidney stones (from fat malabsorption increasing oxalate absorption), nerve damage from B12 deficiency, and severe weight loss. Long-standing untreated celiac disease carries a small increased risk of intestinal lymphoma.

Outlook

The outlook depends on the cause. Lactose intolerance is easily managed with diet. Most people with celiac disease feel much better within weeks of going gluten-free, and the gut lining heals over months to a couple of years. Pancreatic enzyme replacement controls fatty stools well. Short bowel syndrome and severe Crohn's disease need long-term specialist care.

Frequently asked questions

What are the first signs of malabsorption?

Early signs are often chronic diarrhea, bloating and gas after meals, and pale, greasy stools that are hard to flush. Some people first notice tiredness from anemia, unexplained weight loss, or cramps. Children may fail to gain weight or grow normally.

What is the most common cause of malabsorption?

Lactose intolerance is the most common form of malabsorption worldwide. Among conditions that damage the gut, celiac disease is one of the most common in Western countries. Pancreatic insufficiency, Crohn's disease and bacterial overgrowth are other frequent causes.

How do doctors test for malabsorption?

Blood tests check for anemia, vitamin deficiencies and celiac antibodies. Stool tests look for fat, pancreatic enzyme levels, inflammation and parasites. Breath tests diagnose lactose intolerance and bacterial overgrowth. An endoscopy with biopsies of the small intestine confirms celiac disease and other lining problems.

Can malabsorption be cured?

Some causes can be cured, such as infections and bacterial overgrowth. Others, such as celiac disease and lactose intolerance, are lifelong but controlled by diet. Pancreatic insufficiency is managed with enzyme capsules. Treating the cause and replacing nutrients lets most people live normally.

What does malabsorption poop look like?

Fat malabsorption causes stools that are pale or clay-colored, bulky, greasy, very foul-smelling and may float or leave oily droplets in the toilet. Sugar malabsorption causes watery, frothy, acidic stools with a lot of gas.