Welcome to Hydration and Nutrition! (A.2)

Hello future SEHS expert! This chapter, Hydration and Nutrition, is absolutely critical. Why? Because the food we eat and the liquids we drink directly determine how efficiently our body performs, recovers, and adapts to training.
Think of the human body as a high-performance race car: nutrition is the fuel and oil, and hydration is the coolant. Get this wrong, and performance crashes!
We will break down water and electrolyte balance, macronutrients, micronutrients, dietary health concepts like RED-S and the gut microbiome, and specific strategies to maximize athletic output.


Part 1: Water and Electrolyte Balance (A.2.1)

A. Water: The Essential Nutrient

Water makes up about 60% of the body mass in an adult and is essential for virtually every physiological process.

Key Roles of Water in the Body:
  • Transportation: Water is the main component of blood plasma, transporting nutrients, oxygen, and hormones to cells, and removing metabolic waste products (like CO\(_2\) and urea).
  • Temperature Regulation: When we exercise, water absorbs heat and is evaporated from the skin as sweat, cooling the body down.
  • Lubrication: Water helps lubricate joints and mucous membranes (such as the eyes and digestive tract).
  • Cell Structure: Maintains the shape and osmotic integrity of cells.

Analogy: If your body is a city, water is the entire road network, the public transit system, and the air conditioning all rolled into one!

B. Dehydration, Hypernatremia, and Hyponatremia

Maintaining fluid and electrolyte balance is vital for athletic performance and health. Disturbances in water and sodium balance manifest in several specific physiological states:

1. Dehydration and Hypernatremia

Dehydration occurs when fluid loss exceeds fluid intake. Even a 2% loss of body mass due to fluid deficit significantly impairs physical and cognitive performance.

  • Reduced Plasma Volume & Increased Blood Viscosity: Less water in the bloodstream makes blood thicker, increasing cardiovascular strain and heart rate.
  • Thermoregulatory Impairment: Reduced sweating capacity causes core body temperature to rise rapidly.
  • Hypernatremia: When water loss from sweat exceeds sodium loss, blood sodium concentration becomes abnormally high ( elevated plasma osmolality), pulling water out of cells.
2. Hyponatremia (Exercise-Associated Hyponatremia - EAH)

Hyponatremia is an abnormally low concentration of sodium in the blood (plasma sodium < 135 mmol/L). It most commonly occurs in endurance events when an athlete drinks excessive amounts of plain water or hypotonic fluids, diluting the extracellular sodium concentration. This causes fluid to move into cells via osmosis, leading to cellular swelling, confusion, nausea, and in severe cases, cerebral oedema.

Key Term: Electrolytes are minerals (such as sodium, potassium, and chloride) that carry an electrical charge when dissolved in water. They are essential for nerve impulse conduction, muscle contraction, and fluid distribution between cellular compartments.

Quick Review: Monitoring Hydration
A simple practical method to assess hydration status is monitoring urine colour. Pale straw colour indicates adequate hydration, whereas dark yellow or amber indicates dehydration.

Part 2: The Energy Providers - Macronutrients (A.2.2)

Macronutrients are nutrients required in large daily quantities that provide chemical energy to the body. Energy yield is measured in kilojoules (kJ) or kilocalories (kcal).

A. Carbohydrates (CHO)

Carbohydrates are the body’s preferred and most readily available source of energy, particularly during moderate to high-intensity exercise.

  • Structure: Made up of carbon, hydrogen, and oxygen atoms (\(\text{C}_n\text{H}_{2n}\text{O}_n\)). The basic unit is a monosaccharide (e.g., glucose, fructose).
  • Energy Yield: Approximately \(17 \text{ kJ/g}\).
  • Storage: Stored in skeletal muscle and the liver as Glycogen.

B. Fats (Lipids)

Fats provide a dense and abundant fuel source, primarily utilized during rest and low-to-moderate intensity, long-duration exercise.

  • Structure: Primarily stored as triglycerides (one glycerol molecule bound to three fatty acid chains).
  • Energy Yield: Approximately \(37 \text{ kJ/g}\) (more than twice the energy density of carbohydrates or protein).
  • Roles: Long-term energy storage, thermal insulation, protection of vital organs, and carrier for fat-soluble vitamins (A, D, E, K).

C. Protein

Proteins serve primarily as structural and functional components of the body rather than primary fuels.

  • Structure: Formed by chains of amino acids linked by peptide bonds. Essential amino acids cannot be synthesized by the body and must come from the diet.
  • Energy Yield: Approximately \(17 \text{ kJ/g}\) (used as an energy source only under conditions of starvation or prolonged carbohydrate depletion).
  • Roles: Growth and repair of muscle and tissues, synthesis of enzymes, hormones, and immune antibodies.

Part 3: Micronutrients and Gut Health

A. Vitamins and Minerals

Micronutrients do not provide energy directly, but they act as vital co-factors and regulators of metabolic pathways:

  • Water-Soluble Vitamins (B and C): Cannot be stored in large quantities and must be consumed regularly. B vitamins act as essential co-enzymes in energy production pathways (glycolysis and the Krebs cycle).
  • Fat-Soluble Vitamins (A, D, E, K): Absorbed with dietary lipids and stored in adipose tissue and the liver. Vitamin D is essential for calcium homeostasis and bone health.
  • Minerals: Inorganic elements including Calcium (muscle contraction and bone density), Iron (core component of haemoglobin and myoglobin for oxygen transport), and Sodium/Potassium (fluid balance and nerve action potentials).

B. The Gut Microbiome

The gut microbiome consists of trillions of microorganisms residing in the gastrointestinal tract. In athletes, a diverse and healthy gut microbiome plays crucial roles in:

  • Enhancing nutrient digestion and absorption.
  • Supporting the immune system and mucosal barrier function.
  • Producing short-chain fatty acids (SCFAs) that support gut integrity and metabolic regulation.

Part 4: Energy Balance, LEA, and RED-S

Athletes require adequate energy availability to match their high training workloads while maintaining standard physiological functions.

Low Energy Availability (LEA) & RED-S

  • Low Energy Availability (LEA): Occurs when dietary energy intake is insufficient to support physiological functions after subtracting the energy expended in exercise.
  • Relative Energy Deficiency in Sport (RED-S): A clinical syndrome resulting from chronic LEA that impairs metabolic rate, menstrual function, bone health, immunity, protein synthesis, and cardiovascular/psychological health, substantially reducing athletic performance.

Part 5: Fuelling Strategies and Ergogenic Aids

A. Periodised Fuelling Strategies

  • Pre-Exercise: High in low-to-moderate glycaemic index (GI) carbohydrates 2–4 hours prior to maximize glycogen stores without rapid blood glucose spikes.
  • During Exercise: For prolonged endurance exercise (>60 minutes), consume 30–60 g of carbohydrates per hour (often via sports drinks or gels) to spare muscle glycogen and maintain blood glucose levels.
  • Post-Exercise: The recovery window prioritizes rapid glycogen resynthesis and muscle repair using a 3:1 or 4:1 carbohydrate-to-protein ratio.

B. Nutritional Ergogenic Aids

An ergogenic aid is any substance or technique that improves energy production, performance, or recovery:

  • Creatine: Increases muscle phosphocreatine (PCr) stores, enhancing ATP resynthesis in the ATP-PC system during repeated high-intensity, short-duration bouts (e.g., sprinting, resistance training).
  • Caffeine: Acts as a central nervous system (CNS) stimulant, reducing the rate of perceived exertion (RPE) and promoting fat mobilization.
  • Sodium Bicarbonate: Acts as an extracellular buffer against accumulating hydrogen ions (\(\text{H}^+\)) during intense anaerobic glycolysis, delaying muscular acidosis and fatigue.