For Students
How digestion works: from bite to absorption
Every macronutrient takes a different path through digestion before it can actually be used by your body.
| Stage | What happens |
|---|---|
| Mouth | Chewing and salivary enzymes begin breaking down starches |
| Stomach | Acid and enzymes (like pepsin) begin breaking proteins into smaller peptides |
| Small intestine | The main site of digestion and absorption: pancreatic enzymes finish breaking down protein into amino acids, fat into fatty acids (with help from bile), and carbs into simple sugars — all absorbed into the bloodstream here |
| Large intestine | Water is absorbed, and fiber that wasn't digested is fermented by gut bacteria |
The speed of this process varies by macronutrient and food: simple sugars are absorbed fastest, protein and fiber-rich complex carbs take longer, and fat slows digestion of everything eaten alongside it — one reason meals with a mix of macronutrients tend to produce a more gradual, sustained energy release than any single macronutrient eaten alone.
Keep reading: Simple vs. complex carbs · Why fiber matters · What is the glycemic index?