Nutrition, hydration and energy balance
Nutrition, hydration and energy balance examines how food and fluid support performance, recovery and health. SEC questions often ask you to calculate energy intake, explain glycogen use or advise on hydration.
Nutrients and energy
- Carbohydrate: 4 kcal/g; main fuel for high-intensity exercise; stored as glycogen in liver and muscle.
- Protein: 4 kcal/g; builds and repairs tissue; not a major fuel at rest.
- Fat: 9 kcal/g; main fuel at low intensity; provides essential fatty acids and fat-soluble vitamins.
- Micronutrients: vitamins and minerals do not supply energy but support metabolism, bone health and oxygen transport (iron).
Energy balance: energy intake equals energy expenditure for weight maintenance; surplus favours gain, deficit favours loss. Glycaemic index describes how quickly a carbohydrate food raises blood glucose.
Hydration
Dehydration raises heart rate and perceived effort and impairs thermoregulation. Water is usually adequate for activity under about 60 minutes; electrolyte drinks suit longer or hot conditions. Pre-competition meals should be familiar, carbohydrate-rich and low in fat and fibre.
Worked example
A snack contains 50 g carbohydrate, 10 g protein and 5 g fat. Energy = (50 × 4) + (10 × 4) + (5 × 9) = 200 + 40 + 45 = 285 kcal. The reasoning is to apply the correct kcal/g factor to each macronutrient, not to total grams.
Traps
Treating protein as the main energy source; using 4 kcal/g for fat; advising a large untried meal before competition; ignoring fluid lost through sweat.