Macronutrients — Carbohydrates, Fats and Proteins

A balanced diet provides all the nutrients the body needs in the right proportions. This lesson focuses on the three macronutrients — carbohydrates, fats and proteins — which provide the body with energy and are needed in large amounts. For AQA GCSE PE, you must know the recommended ratios, the role of each macronutrient, and how they relate to sporting performance.

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What Are Macronutrients?

Macronutrients are nutrients that the body needs in large quantities to provide energy and support growth and repair. There are three macronutrients:

Macronutrient	Energy per Gram	Main Role
Carbohydrates	4 Kcal/g	The body's main and preferred source of energy
Fats (lipids)	9 Kcal/g	Energy source, particularly at low intensity; insulation and protection of organs
Proteins	4 Kcal/g	Growth and repair of body tissues, including muscle

Exam Tip: Notice that fat provides more than double the energy per gram compared to carbohydrates and proteins (9 Kcal vs 4 Kcal). This is a commonly tested fact. However, carbohydrates are still the body's preferred energy source because they can be broken down more quickly.

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Recommended Macronutrient Ratios

For a balanced diet, the AQA specification states the following proportions:

Macronutrient	Recommended Percentage of Total Daily Calories
Carbohydrates	55–60%
Fats	25–30%
Proteins	15–20%

pie title Recommended Macronutrient Ratios
    "Carbohydrates (55-60%)" : 57.5
    "Fats (25-30%)" : 27.5
    "Proteins (15-20%)" : 15

These ratios may be adjusted depending on the type of sport or activity a person does:

Type of Athlete	Adjustment
Endurance athlete	May increase carbohydrate intake to 60–70% for sustained energy
Strength/power athlete	May increase protein intake to 20–30% for muscle repair and growth
Weight management	May reduce fat intake while maintaining carbohydrate and protein levels

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Carbohydrates — The Body's Main Energy Source

What Are Carbohydrates?

Carbohydrates are the body's primary and preferred source of energy. They are broken down into glucose, which is transported in the blood to cells where it is used for energy.

Types of Carbohydrates

Type	Description	Examples	Speed of Energy Release
Simple carbohydrates	Small sugar molecules; broken down quickly	Sugar, sweets, fruit juice, honey, white bread	Fast (quick energy)
Complex carbohydrates	Long chains of sugar molecules; broken down slowly	Pasta, rice, bread, potatoes, oats, cereals	Slow (sustained energy)

Role of Carbohydrates in Exercise

Role	Detail
Main energy source during exercise	Glucose from carbohydrates fuels muscle contractions
Stored as glycogen	Excess glucose is stored as glycogen in muscles and the liver for later use
Essential for high-intensity exercise	The body relies almost entirely on carbohydrates during high-intensity activity (anaerobic)
Carbohydrate loading	Endurance athletes increase carbohydrate intake in the days before competition to maximise glycogen stores

Exam Tip: When explaining why carbohydrates are the main energy source, mention that they can be broken down quickly to release energy. Fat can also provide energy, but it is broken down much more slowly and is therefore the primary fuel source only during low-intensity exercise.

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Fats — Energy at Low Intensity

What Are Fats?

Fats (also called lipids) are a concentrated source of energy. They provide the most energy per gram of any macronutrient (9 Kcal/g) and play several important roles in the body.

Types of Fats

Type	Description	Examples	Health Effect
Saturated fats	Solid at room temperature; mainly from animal sources	Butter, cheese, fatty meat, cream	Increase LDL cholesterol; linked to heart disease
Unsaturated fats	Liquid at room temperature; mainly from plant sources	Olive oil, nuts, avocado, oily fish	Can reduce LDL cholesterol; healthier option

Role of Fats in Exercise and the Body