19/11/2025
Digestion Explained Simply: Where Each Nutrient Is Absorbed
Your gut isn't just a simple tube. Different nutrients are absorbed at different times. Here's a simplified overview:
1️⃣ Mouth and Stomach
Carbohydrates begin to be broken down by salivary amylase.
Proteins are broken down by stomach acid and pepsin.
Vitamin B12 binds to intrinsic factor at this stage.
🟢 Example: Without stomach acid, vitamin B12 cannot be properly absorbed.
2️⃣ Liver and Gallbladder
Bile salts emulsify fats, making them easier to digest with enzymes.
🟢 Example: Bile acts like dish soap, breaking down fats into finer droplets.
3️⃣ Pancreas
It releases enzymes into the small intestine: amylases for carbohydrates, proteases for proteins, and lipases for fats. 🟢 Example: These enzymes complete the breakdown of food into digestible units.
4️⃣ Duodenum (first part of the small intestine)
Carbohydrates → disaccharides.
Proteins → amino acids.
Lipids → monoglycerides + fatty acids.
🟢 Example: This is where most of the chemical digestion takes place.
5️⃣ Jejunum (middle part of the small intestine)
Primary absorption site: sugars, amino acids, iron, calcium, folate, and fat-soluble vitamins (A, D, E, K).
🟢 Example: Low stomach acid or a lack of bile leads to poor nutrient absorption at this stage.
6️⃣ Ileum (end of the small intestine)
Absorption of vitamin B12 and intrinsic factor.
Recycling of bile salts to the liver. 🟢 Example: People with Crohn's disease affecting the ileum often have a vitamin B12 deficiency.
7️⃣ Colon (large intestine)
Absorbs water, sodium, potassium, and residual bile salts.
🟢 Example: This is why diarrhea leads to dehydration. Water absorption is insufficient at this level.
Each nutrient has its own "checkpoint" in the intestine. Carbohydrates, proteins, and fats are primarily absorbed in the jejunum, vitamin B12 in the ileum, and water and electrolytes in the colon. Proper digestion depends on gastric acidity, bile, enzymes, and the proper functioning of each segment of the intestine.
