Malabsorption is impaired digestion or absorption of nutrients in the small intestine. It can result from a problem in the lumen (not enough enzymes or bile), the mucosa (damaged absorptive surface), or transport (lymphatic or vascular obstruction).
| Cause | Mechanism | Key clue |
|---|
| Celiac disease | Immune reaction to gluten (wheat, barley, rye) flattens the villi of the proximal small intestine | Diarrhea, weight loss, iron-deficiency anemia, dermatitis herpetiformis; may be silent |
| Lactose intolerance | Lactase deficiency; undigested lactose draws water into the bowel and is fermented | Bloating, gas, diarrhea after dairy; very common in adults of Asian and African ancestry |
| Exocrine pancreatic insufficiency | Chronic pancreatitis, cystic fibrosis, pancreatic surgery or cancer — too little lipase | Steatorrhea, weight loss |
| Small intestinal bacterial overgrowth (SIBO) | Bacteria deconjugate bile acids, so micelles cannot form and fat is not absorbed | Bloating, diarrhea, B12 deficiency; after surgery or with motility disorders |
| Crohn disease of the terminal ileum / ileal resection | Loss of the site that absorbs vitamin B12 and bile acids | B12 deficiency, bile-acid diarrhea |
| Short bowel syndrome | Extensive resection leaves too little absorptive surface | High-volume diarrhea, dehydration, multiple deficiencies |
| Tropical sprue, infections (Giardia), bariatric surgery, some drugs | Mucosal injury or bypass | Travel/residence history, surgical history |
Where nutrients are absorbed: iron and calcium mainly in the duodenum; folate in the jejunum; vitamin B12 (with intrinsic factor) and bile salts in the terminal ileum. Fat-soluble vitamins (A, D, E, K) need bile and lipase, so any fat malabsorption also causes their deficiency.
Stool
- Steatorrhea: pale or gray, bulky, greasy, foul-smelling, floating stools that are hard to flush
- Watery diarrhea (carbohydrate malabsorption), gas and bloating
General
- Weight loss despite adequate intake, fatigue, muscle wasting, edema (low protein)
Deficiency signs
| Nutrient | Deficiency findings |
|---|
| Vitamin A | Night blindness, dry eyes, dry skin |
| Vitamin D / calcium | Bone pain, osteomalacia, osteoporosis, hypocalcemia (tetany, Chvostek and Trousseau signs) |
| Vitamin E | Peripheral neuropathy, ataxia, hemolysis |
| Vitamin K | Easy bruising, bleeding, prolonged PT/INR |
| Iron, folate, B12 | Anemia (microcytic with iron; macrocytic with folate or B12); B12 also causes neuropathy and cognitive change |
| Thiamine (B1) | Neuropathy, heart failure (beriberi), Wernicke encephalopathy — a water-soluble vitamin |
| Potassium, magnesium | Weakness, cramps, dysrhythmias |
| Zinc, protein | Rash, poor wound healing, hair loss, edema |
Malabsorption therefore affects blood, heart rhythm, skin, bone, and nerves — not just the gut.
| Test | Use |
|---|
| 72-hour quantitative fecal fat | Confirms fat malabsorption; client eats a set fat intake (about 100 g/day) during collection. More than about 7 g of fat per day is abnormal |
| Qualitative fecal fat (Sudan stain) | Screening |
| Fecal elastase | Low in pancreatic insufficiency |
| Tissue transglutaminase IgA (tTG-IgA) with total IgA | First-line test for celiac disease; client must be eating gluten at the time of testing — do not start the diet before testing; clients already gluten-free may need a supervised gluten challenge. Total IgA identifies IgA deficiency, which causes false negatives; if IgA-deficient, IgG-based tests (DGP-IgG or tTG-IgG) are used |
| Upper endoscopy with duodenal biopsies | Confirms celiac disease (villous atrophy) |
| Hydrogen breath test | Lactose intolerance, SIBO |
| CBC, iron, ferritin, folate, B12, albumin, electrolytes, calcium, magnesium, PT/INR, vitamin D | Extent of deficiency |
| Imaging (CT/MR enterography), stool studies | Crohn disease, pancreatic disease, parasites |
Treat the cause and replace what is missing.
Celiac disease — strict, lifelong gluten-free diet
- Eliminate wheat, barley, rye, and their derivatives (malt, many beers). Pure oats are tolerated by most, but oats are often cross-contaminated — use certified gluten-free oats
- Rice, corn, potatoes, cassava, quinoa, meat, fish, eggs, fruit, vegetables, and most dairy are naturally gluten-free
- Hidden gluten: sauces (soy sauce often contains wheat), gravies, processed meats, soups, some medications and supplements
- Correct deficiencies (iron, folate, vitamin D, calcium); bone density testing as advised
- Screen first-degree relatives and people with type 1 diabetes, who have higher celiac risk
Lactose intolerance — reduce lactose to the tolerated amount; lactase enzyme tablets; yogurt and aged cheeses are often tolerated; maintain calcium and vitamin D intake from other sources.
Pancreatic enzyme replacement therapy (PERT) — pancrelipase
- Take with the first bite of every meal and snack (splitting the dose during a long meal is acceptable), so enzymes mix with food
- Swallow capsules whole; do not crush or chew the enteric-coated beads. If unable to swallow, open the capsule and sprinkle beads on a small amount of acidic soft food (e.g., applesauce) and swallow without chewing; do not mix with milk or other alkaline foods, and do not hold in the mouth (mucosal irritation)
- Adverse effects: abdominal pain, hyperuricemia, and fibrosing colonopathy with very high doses; product is of porcine origin — discuss with clients who avoid pork
- Effectiveness is judged by fewer, more formed stools and weight gain
SIBO — antibiotics (e.g., rifaximin), treat the underlying motility or anatomic cause.
Short bowel syndrome
- Oral rehydration solution; small frequent meals; separate fluids from solid meals if they worsen output
- Fat as medium-chain triglycerides (MCT) — absorbed directly into the portal circulation without micelles or lymphatic transport
- Antidiarrheals (loperamide — do not exceed the prescribed dose; very high doses cause serious cardiac dysrhythmias), acid suppression
- Teduglutide (GLP-2 analog) increases absorptive capacity; can accelerate growth of existing neoplasms, so colonoscopy surveillance is required
- Parenteral nutrition (PN) when enteral intake cannot meet needs — central line care, glucose monitoring, liver function monitoring
- Bile-acid diarrhea: bile acid sequestrants (cholestyramine) — bind other drugs and fat-soluble vitamins; give other drugs 1 hour before or 4–6 hours after
Vitamin replacement — oral or IM/SC vitamin B12 for ileal disease or pernicious anemia; water-miscible forms of fat-soluble vitamins; vitamin K for prolonged INR.
Tropical sprue — folic acid plus a prolonged course of tetracycline (avoid in pregnancy and in young children).
Listed in priority order.
- Fluid and electrolyte balance
- Monitor intake and output, stool frequency and volume, daily weight, orthostatic vital signs
- Monitor potassium, magnesium, calcium; cardiac monitoring if potassium or magnesium is severely low
- Replace fluids and electrolytes as ordered
- Bleeding and safety
- Assess for bruising and bleeding with vitamin K deficiency; check INR before invasive procedures
- Fall precautions with weakness, orthostatic hypotension, or neuropathy
- Nutrition
- High-calorie, high-protein meals given in small, frequent portions; limit fat when steatorrhea is severe (use MCT oil if ordered)
- Dietitian referral for gluten-free or lactose-reduced planning
- When starting PN or enteral feeding in a severely malnourished client, watch for refeeding syndrome (low phosphate, potassium, magnesium; fluid overload)
- Skin integrity — perianal care after each stool; barrier cream
- Medication administration — PERT with meals; separate bile acid sequestrants from other drugs; B12 injections as scheduled
- Accurate stool collection — keep 72-hour fecal fat samples complete and uncontaminated with urine
Celiac disease
- The gluten-free diet is lifelong; even small amounts of gluten damage the intestine, though symptoms may not appear
- Read food labels; ask about ingredients when eating out; avoid shared toasters and cutting boards
- Check medications and supplements for gluten fillers
- Symptoms often improve within weeks; the intestine may take months to years to heal
Pancreatic enzymes — take with every meal and snack; never on an empty stomach; do not chew beads; report persistent greasy stools or abdominal pain.
General
- Keep a food and symptom diary to identify triggers
- Recognize dehydration (thirst, dark urine, dizziness) and electrolyte loss (weakness, cramps, palpitations)
- Take vitamin and mineral supplements exactly as prescribed; keep follow-up blood tests
- Report bleeding or bruising, numbness or tingling, muscle cramps, or weight loss
| Complication | What to watch for |
|---|
| Dehydration and electrolyte imbalance | Hypotension, oliguria, weakness, dysrhythmias (low K⁺, low Mg²⁺) |
| Bleeding from vitamin K deficiency | Bruising, bleeding gums, high INR |
| Hypocalcemia | Tetany, paresthesias, Chvostek and Trousseau signs, seizures |
| Anemia | Fatigue, pallor, dyspnea, tachycardia |
| Osteoporosis / osteomalacia | Bone pain, fractures |
| Refeeding syndrome | Low phosphate, weakness, heart failure, respiratory failure after nutrition starts |
| Intestinal lymphoma | Refractory celiac disease with weight loss and pain |
| PN complications | Central line bloodstream infection, hyperglycemia, liver disease |
- Hallmark stool: pale, bulky, greasy, foul-smelling, floating (steatorrhea)
- Fat malabsorption → deficiency of vitamins A, D, E, K; vitamin K → bleeding and high INR
- Terminal ileum absorbs B12 and bile salts → Crohn ileitis or ileal resection causes B12 deficiency
- Confirm fat malabsorption with a 72-hour fecal fat collection
- Celiac: no wheat, barley, rye — lifelong; test with tTG-IgA and total IgA while still eating gluten
- SIBO: bacteria deconjugate bile acids, impairing fat absorption
- PERT: with the first bite of meals and snacks, swallow whole
- Short bowel: MCT is absorbed into the portal vein without micelles
- Diet: high-calorie, high-protein, small frequent meals, low fat when steatorrhea is severe
- Neuropathy with heart failure (wet beriberi) points to thiamine (water-soluble); neuropathy alone can also come from vitamin E or B12 deficiency
Country Notes
United States
- Packaged foods labeled "gluten-free" must meet an FDA standard of less than 20 parts per million gluten.
- Vitamin D is often reported in ng/mL (multiply by 2.5 for nmol/L).
Philippines
- Rice, corn, and root crops make a gluten-free diet practical, but many sauces and processed foods (soy sauce, breaded items, instant noodles) contain wheat.
- Lactose intolerance is common in adults; teach alternative calcium sources (small fish eaten with bones, tofu, leafy greens).
- Intestinal parasites (e.g., Giardia) and tropical sprue are part of the differential in chronic diarrhea with weight loss.