Nutrients and what they do

Food gives us energy and the building blocks we need to grow and stay healthy. Each nutrient has its own job.

Key Stage 3
About 17 minutes

Macronutrients

Macronutrients are needed in large amounts:
Protein: growth, repair and maintenance of the body. Found in meat, fish, eggs, dairy, beans, lentils and tofu.
Carbohydrate: the body's main source of energy. Starchy carbohydrates are found in bread, rice, pasta and potatoes; sugars in fruit, milk and sweet foods.
Fat: energy, insulation and fat-soluble vitamins (A, D, E, K). Saturated fat (butter, fatty meat) should be limited; unsaturated fat (plant oils, oily fish, nuts) is healthier.

Micronutrients

Micronutrients are vitamins and minerals, needed in small amounts:

Nutrient	Job	Good sources
Vitamin A	Helps you see in dim light; healthy skin	Liver, dairy, carrots
Vitamin C	Helps the body absorb iron; keeps skin, blood vessels and bones healthy	Citrus fruit, peppers, strawberries
Vitamin D	Helps the body absorb calcium	Sunlight on skin, oily fish, eggs
Calcium	Strong bones and teeth	Milk, cheese, yoghurt, fortified alternatives
Iron	Makes red blood cells that carry oxygen	Red meat, beans, dark green vegetables, fortified cereals

Fibre, water and energy

Fibre keeps the digestive system healthy and helps prevent constipation. Adults should aim for 30 g a day. It is found in wholegrain foods, fruit, vegetables, beans and lentils.
Water is needed for almost every process in the body.
Energy in food is measured in kilocalories (kcal). Each gram of carbohydrate or protein gives about 4 kcal; each gram of fat gives about 9 kcal.

Worked example

A snack contains 20 g carbohydrate, 5 g protein and 10 g fat. Estimate its energy.

Carbohydrate: 20 × 4 = 80 kcal.
Protein: 5 × 4 = 20 kcal.
Fat: 10 × 9 = 90 kcal. Total = 80 + 20 + 90 = 190 kcal.

Answer: About 190 kcal.

Key idea

Macronutrients (protein, carbohydrate, fat) are needed in large amounts; micronutrients (vitamins and minerals) in small amounts. Protein builds and repairs; carbohydrate gives energy; vitamin C helps absorb iron; vitamin D helps absorb calcium. Fat gives 9 kcal per gram.

Key words

Macronutrients: Nutrients needed in large amounts: protein, carbohydrate and fat.
Micronutrients: Nutrients needed in small amounts: vitamins and minerals.
Fish: Eat at least 2 portions of fish a week, one of them oily.
Fibre: Adults should aim for 30 g of fibre a day.
Energy in food: About 4 kcal per gram of carbohydrate or protein, and about 9 kcal per gram of fat.

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Common mistakes

Not “Vitamin C”. Vitamin C helps absorb iron, not calcium.

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Extra practice

2 more questions

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Which food is a good source of protein?
1. Lentils
2. Apples
3. Butter
4. Sugar
Show the answer
Answer: Lentils
Lentils are a plant protein.
Which food is mainly carbohydrate?
1. Chicken
2. Cheese
3. Rice
4. Butter
Show the answer
Answer: Rice
Rice is a starchy carbohydrate.

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Sources and references

Checked by the GCSE-ready editorial team, 16 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.