What is a balanced diet and how does nutrition affect performance?
The components of a balanced diet, the role of each nutrient, energy balance and how diet and hydration affect performance.
A focused answer to AQA GCSE PE on diet and nutrition: the components of a balanced diet, the role of each nutrient, energy balance and the effect of diet, hydration and carbo-loading on performance.
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What this dot point is asking
AQA wants you to list the components of a balanced diet, state the role of each nutrient, explain energy balance, and describe how diet and hydration affect performance.
A balanced diet
Energy balance
Active performers need more energy, so they eat more, but the balance between intake and use still decides body weight.
Hydration and performance
Staying hydrated is vital: dehydration thickens the blood, raises the heart rate and reduces performance and concentration, so athletes drink before, during and after exercise. Endurance athletes may use carbo-loading, eating extra carbohydrate in the days before a long event to maximise their glycogen stores and delay fatigue.
The detail behind hydration is worth knowing. When the body loses water through sweat and it is not replaced, blood plasma volume falls, so the blood becomes thicker (more viscous). The heart must beat faster to pump this thicker blood, and less heat is lost, so core temperature rises. The result is earlier fatigue, muscle cramps, slower reactions and reduced concentration, all of which damage performance. This is why endurance athletes drink little and often rather than waiting until they feel thirsty, by which point performance has already dropped.
Different performers need different diets because their activity demands differ. An endurance athlete eats a high proportion of carbohydrate to refill glycogen, a strength or power athlete eats more protein to support muscle repair and growth after resistance training, and everyone needs a balanced spread of vitamins, minerals, fibre and water. The energy nutrients also differ in how quickly they release energy: carbohydrate is the fastest and the body's preferred fuel for high-intensity work, while fat is a slow-release store used more during long, low-intensity activity.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20183 marksExplain why a marathon runner would eat a diet high in carbohydrate in the days before a race.Show worked answer →
A Paper 2 application question linking a nutrient to an endurance event.
Award marks for: carbohydrate is the main and quickest energy source; eating extra carbohydrate (carbo-loading) maximises the glycogen stored in the muscles and liver. During the marathon this larger store provides aerobic energy for longer, delaying fatigue and the point at which the runner "hits the wall".
The application mark needs the link to the long aerobic demand of the marathon, not just "carbs give energy".
AQA 20212 marksA performer takes in 2800 kcal of energy in a day and uses 2500 kcal. State whether they are in positive or negative energy balance and explain the effect on body weight.Show worked answer →
A Paper 2 energy-balance item testing the in-versus-out idea. One mark for the state, one for the effect.
Energy intake ( kcal) is greater than energy output ( kcal), a surplus of kcal, so the performer is in positive energy balance. The body stores the excess energy as fat, so over time body weight increases.
Markers want the correct term (positive energy balance) and the consequence (weight gain through fat storage).
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Sources & how we know this
- AQA GCSE Physical Education (8582) specification — AQA (2016)