Paul Wischmeyer/LinkedIn
Feb 17, 2026, 15:42
Paul Wischmeyer: Nutrient Absorption in the GI Tract
Paul Wischmeyer, Professor of Anesthesiology and Surgery with Tenure at Duke University School of Medicine, shared a post on LinkedIn:
“Nutrient Absorption in the GI Tract
How and Where Nutrients Are Absorbed
Duodenum (mixing plus minerals)
- Acid plus bile plus pancreatic enzymes meet here
- Iron uptake is primarily proximal (risk: low iron if proximal disease/bypass)
- Calcium/Mg begin early; vitamin D status matters
- Folate tends to be more proximal
Jejunum (macronutrient workhorse)
- Carbs: brush-border digestion → glucose/galactose/fructose absorption
- Protein: amino acids + small peptides via high-capacity transport
- Fat: micelles deliver lipids for absorption (needs bile + enzymes)
- Many water-soluble vitamins are absorbed across the small bowel
Ileum (specialists)
- B12 requires intrinsic factor + terminal ileum receptors
- Bile acid recycling preserves the bile pool → supports fat + A/D/E/K absorption
Colon (salvage + microbiome)
- Reclaims water, Na⁺, Cl⁻
- Fiber → microbiome → SCFAs (e.g., butyrate) that fuel colon cells and support barrier function
- Some vitamin K/biotin from microbial activity
- Why this infographic matters in real life:
If someone has:
- Crohn’s in the terminal ileum to think B12 deficiency + bile acids
- Celiac (proximal small bowel) to think iron, folate, calcium deficiency
- Pancreatic insufficiency / cholestasis to think fat plus fat-soluble vitamins (A/D/E/K) deficiency
- Short bowel or bariatric bypass to think site-specific + global malabsorption risk
Understanding the map helps you understand the labs, symptoms, and fixes.”
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