Poor absorption: signs, causes, tests, and what you can do

Poor absorption is when your body can't pull enough nutrients or medicine out of food or pills. You might feel tired, lose weight, have loose stools, or notice new deficiencies like low iron or B12. If pills don’t seem to work or vitamins don’t fix a gap, poor absorption could be the reason.

Common causes and how they affect absorption

Many things can cause poor absorption. Celiac disease damages the small intestine and blocks nutrient uptake. Crohn’s disease and surgeries that remove parts of the gut can do the same. Pancreatic insufficiency stops enzymes that break food down. Medications matter too: long-term proton pump inhibitors can cut B12 and magnesium uptake, and orlistat-style weight loss drugs block fat and fat-soluble vitamin absorption. Small intestinal bacterial overgrowth (SIBO) and chronic diarrhea also steal nutrients before they can be absorbed.

Quick tests and practical fixes

Start with a simple checkup. Blood tests for iron, B12, vitamin D, calcium, and basic blood count give quick clues. A stool fat test shows if you’re losing fat in stool. Breath tests look for SIBO or lactose intolerance. Your doctor may order endoscopy with biopsies when celiac or inflammation is suspected. Pancreatic function tests help when enzyme loss is likely.

Treatment targets the cause and fills gaps. If a medication reduces absorption, ask your prescriber if it can be changed or timed differently. For fat malabsorption, a common fix is pancreatic enzyme replacement (pancrelipase) taken with meals. Fat-soluble vitamins A, D, E, and K may need higher doses or special formulations. B12 deficiency often improves faster with injections or high-dose oral B12 that bypasses poor gut uptake.

Smart habits help too. Take iron on an empty stomach with vitamin C for better uptake, but avoid taking it with calcium or coffee. For drugs that require stomach acid, take them away from antacids or PPIs if your doctor approves. Consider liquid, sublingual, or chewable forms if pills aren’t absorbed well.

If you shop online, pick pharmacies with clear contact info, verified reviews, and a pharmacist you can contact. Check product labels for active form and dosing. For example, methylcobalamin or cyanocobalamin choices matter for B12 support. For fat-soluble vitamins, look for emulsified or micellized formulas if fat absorption is poor. Avoid miracle fixes and huge single-dose claims.

Examples: If you're on orlistat (Xenical) expect less fat absorption—talk about supplementing vitamins A,D,E,K and reading our Xenical article. Metformin (Glucophage) can lower B12 over years—check B12 levels and read our Glucophage guide. After bowel surgery, pancreatic enzyme replacement often helps; your doctor will tell you dosing. These are fixes you can ask about today. Start tracking symptoms and labs this week for free.

See a gastroenterologist if simple fixes don’t work, you keep losing weight, or you have persistent diarrhea or severe deficiencies. Early testing avoids long-term problems like bone loss or anemia. With the right tests and a few smart changes, most causes of poor absorption can be managed well.