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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.
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.
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 |
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.
| 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 | 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.
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.
| 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 | Detail |
|---|---|
| Energy source at low intensity | During low-intensity exercise (walking, slow jogging), fats are the primary energy source |
| Insulation | A layer of subcutaneous fat helps maintain body temperature |
| Protection of organs | Fat surrounds vital organs (heart, kidneys, liver) providing cushioning |
| Absorption of vitamins | Fat-soluble vitamins (A, D, E, K) require fat for absorption |
| Energy reserve | Fat stores provide a large reserve of energy for prolonged, low-intensity activity |
| Essential for cell membranes | Fats are a key component of every cell membrane in the body |
Proteins are made up of amino acids and are essential for the growth, repair and maintenance of body tissues — particularly muscle tissue.
| Role | Detail |
|---|---|
| Growth and repair of muscle tissue | After exercise, muscles have micro-tears that need protein for repair and strengthening |
| Growth (especially in young people) | Proteins are essential for growth during childhood and adolescence |
| Enzyme production | Many enzymes (biological catalysts) are proteins |
| Hormone production | Some hormones (e.g. insulin) are proteins |
| Immune function | Antibodies are proteins that fight infection |
| Emergency energy source | If carbohydrate and fat stores are depleted, the body can use protein for energy (though this is not ideal) |
| Type of Athlete | Protein Need |
|---|---|
| Strength/power athletes | Higher protein requirements to support muscle growth and repair (weightlifters, sprinters, rugby players) |
| Endurance athletes | Moderate protein requirements for muscle repair after prolonged exercise |
| General population | Standard protein intake (15–20% of diet) is sufficient for everyday needs |
Exam Tip: A common exam question asks about the role of proteins in sport. The key answer is growth and repair of muscle tissue. After exercise, muscles experience micro-tears — protein provides the amino acids needed to repair and strengthen the muscle. This is why athletes consume protein after training.
The timing of macronutrient intake matters for athletic performance:
| When | What to Eat | Why |
|---|---|---|
| 3–4 hours before exercise | Complex carbohydrates (pasta, rice) | Provides slow-release energy; tops up glycogen stores |
| During exercise | Simple carbohydrates (energy gels, sports drinks) for events lasting >60 mins | Quick energy to maintain blood glucose levels |
| Within 30 mins after exercise | Protein and simple carbohydrates | Protein for muscle repair; carbohydrates to replenish glycogen stores |
| Macronutrient | Recommended % | Kcal/g | Main Role | Best Sources |
|---|---|---|---|---|
| Carbohydrates | 55–60% | 4 | Main energy source | Pasta, rice, bread, potatoes, fruit |
| Fats | 25–30% | 9 | Energy at low intensity; insulation | Oils, nuts, avocado, oily fish, dairy |
| Proteins | 15–20% | 4 | Growth and repair of tissues | Meat, fish, eggs, beans, dairy, nuts |
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