PE38: Diet and Nutrition
Understanding energy balance, the role of macronutrients and micronutrients in sport, dietary fibre, and nutrition strategies for before, during and after exercise.
⚖️ Energy Balance
Energy Balance: The relationship between the calories consumed through food and drink (energy in) and the calories expended through basal metabolic rate and physical activity (energy out). Maintaining energy balance is essential for managing body weight.
Energy Balance Equation:
Energy IN (calories consumed) = Energy OUT (calories expended) → Weight maintained
Energy IN > Energy OUT → Weight gained (excess stored as fat)
Energy IN < Energy OUT → Weight lost (body uses stored fat for energy)
1 kg of body fat ≈ 7,700 kcal
To lose 0.5kg per week: daily deficit of ~550 kcal needed
Energy IN (calories consumed) = Energy OUT (calories expended) → Weight maintained
Energy IN > Energy OUT → Weight gained (excess stored as fat)
Energy IN < Energy OUT → Weight lost (body uses stored fat for energy)
1 kg of body fat ≈ 7,700 kcal
To lose 0.5kg per week: daily deficit of ~550 kcal needed
Components of Energy Expenditure
- Basal Metabolic Rate (BMR): Energy needed for basic life functions (breathing, heartbeat, organ function) - accounts for 60-75% of daily energy expenditure
- Physical Activity: Energy used during exercise and daily movement - most variable component
- Thermic Effect of Food: Energy used to digest, absorb and metabolise food - about 10% of energy expenditure
For Athletes: Performers must carefully manage energy balance to maintain optimal body composition for their sport. Endurance athletes need high calorie intake to fuel training, while athletes in weight-category sports must balance energy to make their weight class.
🍞 Carbohydrates
Carbohydrates: The body's primary and most efficient source of energy, particularly for high-intensity exercise. Carbohydrates are broken down into glucose, which is stored as glycogen in the muscles and liver.
Types of Carbohydrates
- Simple carbohydrates (sugars): Quick-release energy - fruit, honey, sports drinks, sweets
- Complex carbohydrates (starches): Slow-release energy - pasta, rice, bread, potatoes, oats
Role in Sport
- Primary fuel for high-intensity exercise (glycolysis / anaerobic respiration)
- Stored as glycogen in muscles and liver for use during exercise
- Muscle glycogen fuels working muscles during intense activity
- Liver glycogen maintains blood glucose levels during prolonged exercise
- Carbohydrate loading (glycogen supercompensation) maximises stores before endurance events
- Recommended: 55-60% of total daily calorie intake for most athletes
Sporting Example
A marathon runner "carb-loads" in the 3-4 days before a race by consuming 8-10g of carbohydrate per kg of body weight daily. This maximises muscle glycogen stores, delaying the point at which glycogen depletion causes "hitting the wall" (sudden fatigue at around 20 miles).
🥑 Fats (Lipids)
Fats: A concentrated source of energy that provides more than double the calories per gram compared to carbohydrates or protein. Fats are essential for insulation, protection of organs, and as a long-term energy source during low-intensity exercise.
Types of Fats
- Saturated fats: Animal sources (meat, butter, cheese) - should be limited
- Unsaturated fats: Plant and fish sources (olive oil, avocado, salmon, nuts) - healthier option
- Trans fats: Processed foods - should be avoided
Role in the Body and Sport
- Insulation: Subcutaneous fat retains body heat in cold conditions
- Protection: Visceral fat cushions and protects internal organs from impact
- Long-term energy: Primary fuel source during low-intensity, prolonged exercise (aerobic respiration of fatty acids)
- Fat-soluble vitamins: Fats are needed to transport and absorb vitamins A, D, E and K
- Recommended: 25-30% of total daily calorie intake
Sporting Example
An ultra-endurance runner (100-mile race) relies heavily on fat metabolism for energy because fat provides far more energy per gram than glycogen, and glycogen stores would be depleted long before the finish. The body can store enough fat to fuel many hours of low-intensity exercise, making it the primary energy source for endurance events.
🥩 Protein
Protein: A macronutrient made up of amino acids that is essential for muscle repair, growth and recovery after exercise. Protein also plays a role in enzyme production, immune function and hormone synthesis.
Role in the Body and Sport
- Muscle repair: Repairs micro-tears in muscle fibres caused by intense training
- Muscle growth (hypertrophy): Provides the building blocks for new muscle tissue
- Enzyme production: Enzymes control metabolic processes including energy production
- Immune function: Antibodies are proteins that fight infection
- Hormone synthesis: Some hormones (e.g. growth hormone) are protein-based
- Not a primary energy source: Only used significantly for energy when glycogen stores are very low
- Recommended: 12-15% of total daily calorie intake (athletes may need more)
Protein Sources
- Complete proteins (contain all essential amino acids): Meat, fish, eggs, dairy, soy
- Incomplete proteins (missing some amino acids): Beans, lentils, nuts, grains
- Vegetarians can combine incomplete proteins (e.g. rice and beans) to get all essential amino acids
Sporting Example
A weightlifter consumes 1.6-2.0g of protein per kg of body weight daily to support muscle repair and growth after intense resistance training sessions. A 75kg athlete would therefore need 120-150g of protein per day, consumed across meals with a protein-rich snack within 30 minutes of training to maximise the recovery window.
🍊 Vitamins
Vitamins: Organic micronutrients required in small amounts for various metabolic processes. They cannot be synthesised by the body in sufficient quantities and must be obtained from the diet.
Key Vitamins for Sport
| Vitamin | Function | Source |
|---|---|---|
| Vitamin A | Supports immune function and vision | Carrots, liver, sweet potato, spinach |
| Vitamin B complex | Energy release from carbohydrates; red blood cell production | Whole grains, meat, eggs, dairy |
| Vitamin C | Immune function; collagen production for healthy tendons and ligaments; antioxidant | Citrus fruits, peppers, berries, broccoli |
| Vitamin D | Calcium absorption for bone health; immune function | Sunlight, oily fish, eggs, fortified foods |
| Vitamin E | Antioxidant - protects cells from exercise-induced oxidative damage | Nuts, seeds, vegetable oils, avocado |
⛏️ Minerals
Minerals: Inorganic micronutrients essential for various body functions including bone health, oxygen transport and muscle contraction. Like vitamins, they must be obtained from the diet.
| Mineral | Function | Source | Deficiency Effect |
|---|---|---|---|
| Iron | Essential component of haemoglobin in red blood cells; transports oxygen | Red meat, spinach, lentils, fortified cereals | Anaemia - fatigue, reduced oxygen transport, poor endurance |
| Calcium | Bone formation and strength; muscle contraction; blood clotting | Dairy products, leafy greens, fortified plant milk | Osteoporosis - weak, brittle bones; increased fracture risk |
| Sodium | Fluid balance; nerve impulse transmission; muscle contraction | Salt, processed foods, sports drinks | Hyponatraemia (rare); muscle cramps |
| Potassium | Fluid balance; nerve function; muscle contraction | Bananas, potatoes, oranges, dairy | Muscle weakness, cramps, irregular heartbeat |
Iron for Athletes: Iron is particularly important for endurance athletes because it is the core component of haemoglobin, which carries oxygen in red blood cells. Iron deficiency anaemia reduces the blood's oxygen-carrying capacity, directly impairing aerobic performance. Female athletes are at higher risk due to menstrual blood loss.
🌾 Fibre
Dietary Fibre: The indigestible part of plant foods that passes through the digestive system relatively intact. Fibre is essential for healthy digestion and preventing digestive disorders.
Role of Fibre
- Promotes regular bowel movements and prevents constipation
- Reduces the risk of bowel cancer and digestive disorders
- Helps control blood sugar levels by slowing glucose absorption
- Creates a feeling of fullness that helps control appetite
- Lowers cholesterol levels, reducing heart disease risk
- Supports a healthy gut microbiome
Sources of Fibre
- Wholegrain bread, pasta and cereals
- Fruit, vegetables and legumes (beans, lentils)
- Nuts and seeds
- Brown rice and whole oats
Caution for Athletes: High-fibre foods should be avoided immediately before competition as they can cause bloating, gas and stomach discomfort during exercise. Athletes should consume fibre-rich foods in their regular diet but reduce intake in the 24-48 hours before competition.
⏰ Pre-Event, During Event and Post-Event Nutrition
Pre-Event Nutrition (2-4 hours before)
- Focus on complex carbohydrates for sustained energy release
- Moderate protein; low fat and low fibre (slow digestion)
- Meal should be familiar - never try new foods before competition
- Examples: Pasta with tomato sauce, rice with chicken, porridge with banana
- Hydrate well with water in the hours leading up to the event
Pre-Event Snack (30-60 minutes before)
- Simple carbohydrates for quick-release energy
- Easily digestible, small portion
- Examples: Banana, energy bar, sports drink, toast with honey
During Event Nutrition (events lasting over 60 minutes)
- Consume carbohydrates to maintain blood glucose levels
- Sports drinks provide both carbohydrate and hydration
- Energy gels for intense endurance events (marathons, triathlons)
- For events under 60 minutes, water is usually sufficient
- Aim for 30-60g of carbohydrate per hour of exercise
Post-Event Nutrition (within 30-60 minutes after)
- Protein for muscle repair and recovery
- Carbohydrates to replenish glycogen stores
- Combination of both is optimal (3:1 carbohydrate to protein ratio)
- Rehydrate with water or electrolyte drinks
- Examples: Chocolate milk, protein shake with banana, chicken and rice, yoghurt and fruit
| Timing | Focus | Examples |
|---|---|---|
| 2-4 hours pre-event | Complex carbs, moderate protein, low fat/fibre | Pasta with chicken, rice dish, porridge |
| 30-60 min pre-event | Simple carbs, easily digested | Banana, energy bar, sports drink |
| During event (60+ min) | Carbs + hydration | Sports drink, energy gel, banana |
| Post-event (0-60 min) | Protein + carbs + rehydration | Chocolate milk, chicken and rice, protein shake |
❓ Practice Questions
Q1: Explain what is meant by energy balance and how it affects body weight.
Q2: Describe the role of carbohydrates in sport. Why are complex carbohydrates preferred over simple carbohydrates in pre-event meals?
Q3: Explain why iron and calcium are particularly important minerals for athletes.
Q4: Describe what an endurance athlete should eat before, during and after a marathon. Justify your recommendations.
Q5: Why should athletes avoid high-fibre foods in the 24 hours before competition?
Q6: Explain the role of protein in post-exercise recovery and suggest an appropriate post-event meal for a strength athlete.
✅ Answers
- Energy balance is the relationship between calories consumed (energy in from food and drink) and calories expended (energy out from BMR, physical activity and digestion). When energy in equals energy out, body weight is maintained. When energy in exceeds energy out, the excess is stored as fat and weight is gained. When energy out exceeds energy in, the body uses stored fat for energy and weight is lost. Athletes must manage energy balance carefully to maintain optimal body composition for their sport.
- Carbohydrates are the body's primary and most efficient energy source, particularly for high-intensity exercise. They are broken down into glucose and stored as glycogen in muscles and the liver. During exercise, glycogen is converted back to glucose and used for energy through glycolysis. Complex carbohydrates are preferred in pre-event meals because they provide slow, sustained energy release over a longer period, maintaining blood glucose levels throughout the event. Simple carbohydrates provide quick-release energy that may cause a blood sugar spike followed by a crash, which is not ideal for sustained performance.
- Iron is essential for athletes because it is the core component of haemoglobin, the protein in red blood cells that transports oxygen from the lungs to working muscles. Without sufficient iron, oxygen transport is impaired, reducing aerobic capacity and causing fatigue (anaemia). This is especially important for endurance athletes and female athletes who lose iron through menstruation. Calcium is important for athletes because it is essential for bone formation and strength, reducing the risk of stress fractures. Calcium is also required for muscle contraction and blood clotting. Athletes in weight-bearing sports and those with low body weight (which can affect bone density) particularly need adequate calcium.
- Pre-event (2-4 hours before): A meal high in complex carbohydrates (e.g. pasta with tomato sauce) for sustained energy, with moderate protein and low fat/fibre for easy digestion. Pre-event (30 min before): Simple carbohydrate snack (e.g. banana) for quick energy. During the marathon: Sports drinks containing carbohydrates and electrolytes to maintain blood glucose and hydration; energy gels for additional carbohydrate intake (30-60g carbs per hour). Post-event (within 30-60 minutes): A combination of protein and carbohydrates (e.g. chocolate milk or protein shake with banana) for muscle repair and glycogen replenishment, plus water for rehydration.
- Athletes should avoid high-fibre foods before competition because fibre is indigestible and can cause bloating, gas, stomach cramps and diarrhoea during exercise. These gastrointestinal issues are uncomfortable and distracting, and can significantly impair performance. Fibre also slows gastric emptying, meaning food stays in the stomach longer rather than being absorbed for energy. In the 24-48 hours before competition, athletes should reduce fibre intake and focus on easily digestible, low-fibre carbohydrate sources like white rice, white pasta and refined cereals.
- Protein is essential for post-exercise recovery because intense training causes micro-tears in muscle fibres, and protein provides the amino acids needed to repair this damage and rebuild stronger muscle tissue (hypertrophy). The 30-60 minute window after exercise is when muscles are most receptive to protein uptake, making it the optimal time for protein consumption. For a strength athlete, an appropriate post-event meal would be grilled chicken breast with rice and vegetables, or a protein shake with a banana. The chicken/protein shake provides high-quality protein for muscle repair, while the rice/banana provides carbohydrates to replenish glycogen stores. The 3:1 carbohydrate-to-protein ratio supports both recovery goals.
🎯 Exam Tips
- Know the energy balance equation and its three outcomes (maintain, gain, lose weight)
- Carbohydrates = primary energy source; Fats = insulation, protection, long-term energy; Protein = muscle repair and growth
- Iron = haemoglobin = oxygen transport; Calcium = bones and muscle contraction
- Pre-event = complex carbs, low fat/fibre; During = simple carbs + hydration; Post-event = protein + carbs
- Always explain WHY a nutritional strategy is used, not just WHAT to eat
- Use the term "glycogen replenishment" not "replacing energy" for post-event nutrition
⚠️ Common Errors
Watch Out!
Students often say protein is the main energy source. Wrong: "Protein provides the main energy for exercise." Correct: "Carbohydrates are the primary energy source for exercise. Protein is mainly used for muscle repair and growth, and is only used as a significant energy source when glycogen stores are very depleted."
Students often confuse vitamins and minerals. Wrong: "Iron is a vitamin needed for strong bones." Correct: "Iron is a mineral needed for haemoglobin production and oxygen transport. Calcium is a mineral needed for bone strength."
📝 Exam Technique
PE Exam Tips — Diet and Nutrition:
1. For Diet and Nutrition questions, use subject-specific terminology precisely
2. Support every point with specific evidence or examples
3. Show balanced analysis — consider different perspectives before reaching a conclusion
4. Link your understanding of Diet and Nutrition to real-world contexts where possible
5. For longer answers, plan your response to address all parts of the question
1. For Diet and Nutrition questions, use subject-specific terminology precisely
2. Support every point with specific evidence or examples
3. Show balanced analysis — consider different perspectives before reaching a conclusion
4. Link your understanding of Diet and Nutrition to real-world contexts where possible
5. For longer answers, plan your response to address all parts of the question
⚠️ Common Errors
Watch Out!
Students often think you need to be slim to be fit. Wrong: You need to be slim to be fit Correct: Fitness depends on the ability to meet demands placed on you. Sumo wrestlers, rugby forwards and powerlifters may have high body fat but are extremely fit for their sport.
Students often think drinking water during exercise is enough to stay hydrated. Wrong: Drinking water during exercise is enough to stay hydrated Correct: For prolonged exercise (over 60 minutes), electrolyte replacement may also be needed. Drinking too much plain water can cause hyponatraemia (dangerously low sodium).
Students often think obesity is just about eating too much. Wrong: Obesity is just about eating too much Correct: Obesity has multiple causes: genetics, socio-economic factors, sedentary lifestyle, medical conditions, and mental health. It is not simply a matter of willpower or overeating.
✍️ Model Answer
Full-Mark Response
6 marks: Explain how diet and nutrition affects sporting performance.
Diet and Nutrition has significant effects on sporting performance. [Key concept 1]: explain the mechanism with specific detail. [Key concept 2]: how this applies in a named sporting example. [Key concept 3]: the relationship between this topic and overall performance. A grade 9 answer uses precise anatomical/physiological terminology, specific sporting examples, and evaluates the relative importance of different factors.
Mark scheme: 2 marks per explained point with specific evidence, evaluation for top marks
📊 AO Deep Dive
Assessment Objective Analysis
GCSE PE tests four AOs: AO1 (Knowledge, 30%) — recall facts about Diet and Nutrition including definitions, classifications and specific examples; AO2 (Application, 30%) — apply knowledge to sporting contexts and training scenarios; AO3 (Analysis and Evaluation, 25%) — analyse data (graphs, tables), evaluate training methods or strategies, and justify recommendations; AO4 (Practical, 15%) — demonstrate relevant skills. For grade 9, use precise terminology, support every point with named sporting examples, and evaluate rather than just describe. The difference between grade 5 and grade 9 is the quality of application and depth of evaluation.
📝 Exam Questions by Topic
🎬 Video Resources
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