How Digestion Works
Quick answer
Digestion breaks food into smaller components that can be absorbed and used. Mechanical movement, enzymes, acid, bile, microbes and the intestinal lining all contribute.
- Follow food through the digestive tract
- Separate digestion from absorption
- Understand the role of the gut microbiome
Mouth and stomach
Chewing increases surface area. Saliva begins digestion, while the stomach mixes food with acid and enzymes.
Small intestine
Most nutrient digestion and absorption occur here. Pancreatic enzymes and bile help process carbohydrate, protein and fat.
Large intestine
Water and electrolytes are absorbed, and microbes ferment some fibres, producing compounds that interact with the intestinal environment.
A sandwich is not absorbed as “sandwich.” Starch is broken toward simple sugars, protein toward amino acids and fat toward fatty acids and related molecules.
Key terms
| Digestion | Mechanical and chemical breakdown of food. |
|---|---|
| Absorption | Movement of nutrients into blood or lymph. |
| Enzyme | A protein that speeds a chemical reaction. |
| Microbiome | The community of microbes living in a particular environment. |
Common mistakes
- Judging a food by one nutrient while ignoring the whole food and overall eating pattern.
- Turning general public-health guidance into an exact personal prescription.
- Assuming a confident headline is stronger than the evidence behind it.
Practical takeaway
Use this lesson as a framework, not a rulebook. Look at foods in context, favour patterns you can maintain, and seek individual guidance when health conditions, medication, pregnancy, growth or significant dietary restriction change the situation.
Sources and further reading
- MedlinePlus — Carbohydrates
- MedlinePlus — Dietary Proteins
- MedlinePlus — Dietary Fats
- Health Canada — Healthy eating recommendations
- World Health Organization — Healthy diet
Editorial note: NutritionLessons.com summarizes established guidance in plain language. Content is independently prepared from the sources shown and is not individually reviewed by a physician or dietitian. This page provides general education and does not diagnose, treat or replace individualized advice.