Welcome to Nutrition for Health and Exercise!

Welcome to your revision notes for Unit AS 2: The Active Leisure Industry: Health, Fitness and Lifestyle. Whether you love science or sometimes find it tricky, do not worry! We will break down every concept into straightforward, bite-sized steps.

Nutrition is the fuel that powers every single movement of our bodies. In this chapter, we explore what makes up a balanced diet, how our bodies balance energy, how athletes adapt their fuelling before, during, and after exercise, and how diet impacts long-term health. Let's dive in!


1. The Components of a Balanced Diet

A balanced diet provides the right nutrients in the correct proportions to keep the body healthy and working efficiently. Nutrients are split into two main groups: macronutrients (needed in large amounts) and micronutrients (needed in tiny amounts), alongside dietary fibre and water.

A. Macronutrients

1. Carbohydrates:
Carbohydrates are the body's primary and preferred energy source. When digested, they are broken down into glucose and circulated in the bloodstream. Any excess glucose is converted and stored as glycogen in two key locations: the skeletal muscles and the liver.
Analogy: Think of glycogen as your body’s rechargeable battery pack. When you take part in high-intensity exercise (like sprinting or circuit training), your muscles rely almost entirely on these glycogen stores for rapid energy.

2. Proteins:
Proteins are made up of building blocks called amino acids. Their primary roles are growth and tissue repair (especially repairing microscopic tears in muscle fibres caused by strenuous training) and the synthesis of essential enzymes and hormones.
Common Mistake to Avoid: Protein is not a primary energy source during exercise! The body only burns protein for fuel in extreme situations of starvation or total glycogen depletion.

3. Fats (Lipids):
Fats provide a dense, long-term energy reserve, act as thermal insulation beneath the skin, cushion and protect vital internal organs, and transport fat-soluble vitamins (Vitamins A, D, E, and K). Fats are split into:
• Saturated fatty acids: Mainly from animal sources; excessive consumption is linked to health problems.
• Unsaturated fatty acids: Healthier fats found in plant oils, nuts, seeds, and oily fish.
Fats are the predominant fuel source during low-to-moderate intensity aerobic exercise (like a gentle walk or steady jog).

B. Micronutrients, Fibre, and Water

1. Vitamins & Minerals:
These do not provide energy directly, but they are crucial for keeping metabolic processes running smoothly.
• Calcium & Vitamin D: Crucial for developing and maintaining strong bone density.
• Iron: Essential for manufacturing haemoglobin inside red blood cells, which carries oxygen to exercising muscles.
• Vitamins C and E: Act as antioxidants, protecting body cells from damage caused by free radicals during high-intensity training.

2. Dietary Fibre (Non-Starch Polysaccharides):
Fibre cannot be digested by human enzymes, but it is vital for healthy digestion. It promotes healthy gastrointestinal motility (keeps food moving through the digestive tract), maintains bowel health, and helps regulate blood sugar and blood cholesterol levels.

3. Hydration & Water:
Water makes up about 60% of our body mass. It is vital for:
• Thermoregulation: Regulating body temperature by allowing cooling through perspiration (sweating).
• Nutrient and waste transport: Maintaining plasma volume so blood can carry nutrients and oxygen.
• Preventing hypovolemia: Dehydration reduces total blood volume, forcing the heart to work harder (increased heart rate) to maintain cardiac output and blood pressure.

Key Takeaway for Section 1: Carbohydrates provide fast energy (stored as glycogen in muscle and liver), fats provide long-term energy and protection, proteins repair muscle micro-tears, while micronutrients, fibre, and water ensure the body functions smoothly and stays cool.


2. Energy Balance, Requirements, and Metabolism

Energy balance is the relationship between the energy you put into your body through food and drink, and the energy your body expends through daily functions and physical activity.

The Energy Balance Equation

Total daily energy expenditure is made up of three main components:
\( \text{Energy Intake} = \text{Basal Metabolic Rate (BMR)} + \text{Thermic Effect of Food (TEF)} + \text{Physical Activity Level (PAL)} \)

Let's break down each term:
• Basal Metabolic Rate (BMR): The minimum energy required to keep vital organs (heart, lungs, brain) functioning while at complete rest.
• Thermic Effect of Food (TEF): The energy used to ingest, digest, absorb, and metabolise nutrients (usually around 10% of total intake).
• Physical Activity Level (PAL): The additional energy burned through all physical movement, from walking up the stairs to playing a 90-minute football match.

The Three States of Energy Balance

1. Neutral Energy Balance:
\( \text{Energy Intake} = \text{Energy Expenditure} \)
Weight remains stable because calories consumed equal calories burned.

2. Positive Energy Balance:
\( \text{Energy Intake} > \text{Energy Expenditure} \)
More energy is consumed than expended. The excess energy is stored as adipose tissue (body fat), leading to weight gain.

3. Negative Energy Balance:
\( \text{Energy Intake} < \text{Energy Expenditure} \)
Less energy is consumed than expended. The body must break down stored fat and glycogen to meet energy demands, leading to weight loss.

Key Takeaway for Section 2: Maintaining body weight requires balancing intake against your BMR, TEF, and PAL. Consume more than you burn, and you gain weight; consume less, and you lose weight.


3. Nutrition for Health vs. Athletic Performance

Standard dietary advice for the general public differs significantly from the specific nutritional strategies required by athletes.

Public Health Dietary Guidelines

For the general sedentary or moderately active population, UK public health guidelines recommend the following macronutrient split of total dietary energy:
• Carbohydrates: Roughly 50–55% of daily energy intake.
• Total Fats: Less than 35% of daily energy intake (with saturated fats limited to less than 10%).
• Protein: 15–20% of daily energy intake.

Athletic Fuelling: Timing and Periodisation

Athletes place extreme demands on their bodies and require elevated carbohydrate intake (often \(6\text{–}10\,\text{g/kg}\) of body mass per day for endurance performers) along with precise timing strategies:

1. Pre-Exercise Nutrition:
• Timing: Consumed 2.5 to 4 hours prior to exercise.
• Composition: High in complex carbohydrates to top up muscle and liver glycogen, moderate in protein, and low in fat and fibre to avoid gastrointestinal (stomach) discomfort during the event.
• Hydration: Drinking fluids in the hours leading up to competition to achieve euhydration (optimal hydration status).

2. During-Exercise Nutrition:
• Threshold: Needed during continuous exercise lasting longer than 60 minutes.
• Strategy: Consuming carbohydrate-electrolyte solutions (such as isotonic sports drinks containing 4–8% carbohydrate). This maintains blood glucose levels, delays fatigue, and replaces lost electrolytes like sodium and potassium lost through sweat.

3. Post-Exercise Nutrition (The Recovery Window):
Optimal recovery involves the 3 R's: Refuel, Rebuild, and Rehydrate:
• Refuel: Consume \(1.0\text{–}1.2\,\text{g}\) of carbohydrate per kg of body mass per hour for the first 4 hours post-exercise to rapidly restore depleted glycogen stores.
• Rebuild: Consume 20–25 g of high-quality protein soon after exercise to stimulate Muscle Protein Synthesis (MPS) and repair muscular micro-trauma.
• Rehydrate: Consume \(1.25\text{–}1.5\,\text{L}\) of fluid for every 1 kg of body mass lost during the training session or match.

Understanding Sports Drinks and Osmolality

Osmolality describes the concentration of dissolved particles (sugars and electrolytes) in a fluid compared to blood plasma:

• Hypotonic Drinks: Lower concentration of carbohydrates (\(<4\%\)) than blood plasma. Water is absorbed very quickly via osmosis. Best for quick hydration in hot conditions without extra calories.
• Isotonic Drinks: Equal concentration of carbohydrates (4–8%) to blood plasma. They offer the ideal balance between fluid replacement and energy delivery during exercise lasting \(>60\) minutes.
• Hypertonic Drinks: Higher concentration of carbohydrates (\(>8\%\)) than blood plasma. Absorbed slowly because water is initially drawn into the gut. Best used post-exercise or for recovery when high carbohydrate intake is needed.

Key Takeaway for Section 3: The general public needs balanced energy splits, but athletes must time high-carbohydrate meals before events, use isotonic drinks during exercise over 60 minutes, and target the post-exercise window with carbs, 20–25 g protein, and \(1.25\text{–}1.5\,\text{L}\) fluid per kg lost.


Diet-Related Health Conditions

Poor nutrition and chronic positive energy balance can lead to significant lifestyle diseases:

• Cardiovascular Disease (CVD): Diets high in saturated and trans fats elevate low-density lipoprotein (LDL) cholesterol, leading to atherosclerosis (narrowing of arterial walls). High dietary sodium (salt) increases blood pressure (hypertension), further elevating heart attack and stroke risk.
• Type 2 Diabetes: Often triggered by chronic excess energy intake, physical inactivity, and obesity. The body's cells become resistant to insulin, preventing normal glucose uptake and causing chronically high blood sugar levels.
• Obesity: Characterised by a Body Mass Index of \( \text{BMI} \ge 30\,\text{kg/m}^2 \). It results from long-term positive energy balance and dramatically increases the risk of heart disease, joint degradation, and type 2 diabetes.

Ergogenic Aids: Legal Nutritional vs. Prohibited Substances

An ergogenic aid is any substance, technique, or device designed to enhance energy production, recovery, or sports performance.

1. Legal Nutritional Ergogenic Aids:
These are safe and permitted under World Anti-Doping Agency (WADA) regulations:
• Creatine Monohydrate: Increases phosphocreatine (PCr) stores in skeletal muscle, aiding rapid ATP regeneration during short, explosive bursts of exercise (e.g., sprinting, weightlifting).
• Caffeine: A central nervous system stimulant that reduces the perception of effort, increases alertness, and mobilises fatty acids.
• Whey Protein: A fast-digesting, convenient protein source rich in essential amino acids to support Muscle Protein Synthesis (MPS) post-workout.
• Isotonic Sports Drinks: Formulated to supply carbohydrates and electrolytes simultaneously during endurance events.

2. Prohibited Substances:
Substances banned by WADA (such as anabolic steroids or erythropoietin/EPO) because they provide an unfair competitive advantage, carry serious medical and physiological risks, and violate the spirit of sport.

Key Takeaway for Section 4: Poor nutrition leads to conditions like CVD, Type 2 diabetes, and obesity (\(\text{BMI} \ge 30\)). Athletes can legally support performance using aids like creatine, caffeine, whey protein, and sports drinks, while strictly avoiding banned substances.


5. Quick Revision & Common Exam Pitfalls

Top 5 Pitfalls to Avoid in the Exam

1. Don't say "carbohydrates give energy" without detail: Always name glycogen, mention where it is stored (skeletal muscle and liver), and state whether it fuels high-intensity or endurance efforts.
2. Don't confuse protein's role: State clearly that protein is for muscle repair, enzyme production, and Muscle Protein Synthesis (MPS), not primary fuelling during exercise.
3. Don't mix up public advice with athletic needs: The general public needs \(50\text{–}55\%\) carbs, but an endurance athlete requires higher levels (\(6\text{–}10\,\text{g/kg/day}\)) to replenish glycogen depletion.
4. Remember the recovery rehydration rule: You must drink \(1.25\text{–}1.5\,\text{L}\) of fluid per 1 kg of body mass lost, not just 1 litre!
5. Clearly distinguish sports drink osmolality: Hypotonic is low solute/fast water absorption, isotonic is \(4\text{–}8\%\) matching blood plasma, and hypertonic is \(>8\%\) for high-energy recovery.


Quick Check Summary

• Carbs: Primary fuel \(\rightarrow\) stored as muscle & liver glycogen.
• Protein: Repair of micro-tears \(\rightarrow\) 20–25 g post-exercise for MPS.
• Fats: Long-term energy store, organ protection, fat-soluble vitamins (A, D, E, K).
• Energy Balance: \(\text{Intake} = \text{BMR} + \text{TEF} + \text{PAL}\).
• Isotonic Drinks: 4–8% carbohydrate, ideal for sessions lasting \(>60\) minutes.
• Post-Exercise Refuelling: \(1.0\text{–}1.2\,\text{g}\) carbs/kg/hr for 4 hours.