Nutrients and Digestion
Food is fuel and building material, but your body cannot use it until it is broken down into pieces small enough to absorb. That job belongs to digestion. Knowing the main nutrients and the basic steps of digestion answers a whole set of biology questions and explains why a balanced diet matters.
This lesson covers the nutrients your body needs and how digestion begins.
Nutrients are the substances in food that the body uses for energy, growth, and repair. The main groups are carbohydrates, proteins, fats, vitamins, minerals, and water. Digestion is the process of breaking food into small molecules the body can absorb, and it begins in the mouth.
What are the main nutrients?
Food provides several kinds of nutrients, each with a job. Carbohydrates are the body’s main energy source. Proteins build and repair tissues. Fats store energy and support cells. Vitamins and minerals are needed in small amounts to keep processes running. And water, though it has no calories, is essential for nearly every function. A balanced diet supplies all of these in the right amounts.
| Nutrient | Main role |
|---|---|
| Carbohydrates | Main energy source |
| Proteins | Build and repair tissue |
| Fats | Store energy, support cells |
| Vitamins and minerals | Support body processes |
How does digestion begin?
Digestion has two kinds of action working together. Mechanical digestion physically breaks food apart, starting with your teeth chewing. Chemical digestion uses enzymes to break large molecules into small ones; saliva in your mouth already contains an enzyme that starts breaking down starch. From the mouth, food is swallowed and travels down the esophagus to the stomach, where strong acid and more enzymes continue the work.
Watch: A Short Video Lesson
CodeLucky walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:
A routine for nutrition and digestion questions
- Match each nutrient to its job (carbs for energy, protein for building, and so on).
- Remember digestion breaks food into absorbable molecules.
- Separate mechanical (chewing) from chemical (enzymes) digestion.
- Recall that digestion begins in the mouth.
- Enzymes speed up the chemical breakdown of food.
Practice questions
- Which nutrient is the body’s main energy source?
- Which nutrient is used to build and repair tissue?
- Where does digestion begin?
- What is the difference between mechanical and chemical digestion?
- What do enzymes do during digestion?
- True or false: water is an important nutrient even though it has no calories.
Answers:
- Carbohydrates.
- Proteins.
- In the mouth.
- Mechanical physically breaks food apart; chemical uses enzymes to break down molecules.
- They speed up the breakdown of large food molecules into small ones.
- True.
Where this fits
Nutrients and digestion connect to homeostasis, enzymes, and nutrition and lead into how the body absorbs food in digestive organs and absorption. Digestion is one of the major human body systems. Find all topics on the ASVAB General Science Learning Hub.
Recommended Prep Books
These study guides and practice books help you keep building momentum as you prepare:
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