Topic 2.5: Nutrition and Physical Exercise in Maintaining Good Health
Welcome to this study guide for AS 2: Human Body Systems! In this chapter, we explore how the food we eat and the physical activity we perform work together to keep our bodies functioning at their best. We will break down nutrients, uncover what happens when our diet lacks essential components, learn how to calculate and interpret body metrics, and look closely at how our body systems adapt to exercise. Don't worry if some of the physiological terms look daunting at first—we will break each one down step by step!
---1. Balanced Diet and Macronutrients
A balanced diet is defined as a diet that provides the correct proportions of nutrients—including carbohydrates, lipids, proteins, vitamins, minerals, water, and dietary fibre—needed to maintain optimal health and support growth and metabolic demands.
Our body requires large quantities of macronutrients on a daily basis. Let's look at their main physiological roles:
• Carbohydrates: Act as the body's primary energetic substrate. They are broken down into glucose, which cells use during cellular respiration to produce energy.
• Proteins: Essential for growth, tissue repair, and the synthesis of critical biological molecules such as enzymes, hormones, and structural proteins.
• Lipids (Fats): Serve as long-term energy storage, provide thermal insulation against heat loss, cushion and protect vital internal organs, and form structural components of cell membranes (such as phospholipids).
• Dietary Fibre: Non-digestible plant material that provides bulk to aid peristalsis (the muscular contractions of the gut). It promotes gastrointestinal health and significantly reduces the risk of constipation and bowel disorders.
Key Takeaway: Macronutrients fuel our metabolism, build our cellular machinery, and keep our digestive tract functioning properly.
---2. Micronutrients: Roles, Sources, and Deficiency Diseases
Micronutrients are required in much smaller quantities than macronutrients, but a deficiency can lead to serious disorders. In your examination, you must be specific about dietary sources, functions, and the precise symptoms of deficiencies.
A. Vitamin C (Ascorbic Acid)
• Physiological Function: Essential for the synthesis and maintenance of collagen (a structural protein found in skin, blood vessels, and bones). It also acts as an antioxidant and aids the absorption of dietary iron.
• Dietary Sources: Citrus fruits (such as oranges and lemons), blackcurrants, bell peppers, and broccoli.
• Deficiency Disorder: Scurvy.
• Symptoms of Deficiency: Swollen and bleeding gums, easy bruising, petechiae (tiny red or purple spots on the skin caused by minor bleeding), delayed wound healing, and joint or muscle pain.
B. Vitamin D and Calcium
• Physiological Function: Crucial for normal bone and tooth mineralisation and development, as well as proper neuromuscular function.
• Dietary Sources: Oily fish, dairy products, fortified cereals, and synthesised endogenously in the skin through sunlight exposure.
• Deficiency Disorders: Rickets in children (causing soft, weakened, and bowed bones) and Osteomalacia in adults (softening of the bones), along with an increased long-term risk of osteoporosis.
C. Iron (\(Fe^{2+}/Fe^{3+}\))
• Physiological Function: An essential component of haemoglobin, the protein inside red blood cells (erythrocytes) responsible for transporting oxygen throughout the body. It is also an essential part of myoglobin in muscle cells.
• Dietary Sources: Red meat, liver, dark green leafy vegetables (such as spinach), lentils, beans, and fortified cereals.
• Deficiency Disorder: Iron-deficiency anaemia.
• Symptoms of Deficiency: Fatigue, persistent tiredness, general weakness, pallor (pale skin), shortness of breath, palpitations, and dizziness.
Examiner Warning: Never give vague dietary advice in an exam! If a question asks how a patient with iron deficiency can improve their condition, writing "eat healthier" will earn zero marks. You must specify: "increase consumption of lean red meat, liver, or dark leafy greens like spinach." Also, take care not to confuse the symptoms of anaemia (fatigue, breathlessness) with scurvy (bleeding gums, petechiae).
---3. Energy Balance, Body Mass Index (BMI), and Obesity
Energy Balance
Weight management depends on the balance between energy consumed and energy used by the body:
• Energy Balance Equilibrium: \(\text{Energy Intake} = \text{Energy Expenditure}\). Body mass remains stable.
• Positive Energy Balance: \(\text{Energy Intake} > \text{Energy Expenditure}\). Excess energy is converted and stored as adipose tissue, leading to weight gain and potential obesity.
• Negative Energy Balance: \(\text{Energy Intake} < \text{Energy Expenditure}\). The body metabolises its energy stores, resulting in weight loss.
Body Mass Index (BMI)
BMI is a standardised screening tool used to assess whether an individual is a healthy weight for their height.
Formula:
\(\text{BMI} = \frac{\text{Mass in kilograms}}{(\text{Height in metres})^2} = \frac{\text{kg}}{\text{m}^2}\)
Standard BMI Classifications
• Underweight: \(< 18.5\)
• Normal / Healthy weight: \(18.5 - 24.9\)
• Overweight: \(25.0 - 29.9\)
• Obese: \(\ge 30.0\)
Sub-categories:
- Class I Obese: \(30.0 - 34.9\)
- Class II Obese: \(35.0 - 39.9\)
- Class III Obese: \(\ge 40.0\)
Step-by-Step Calculation Example:
A person has a mass of \(80\text{ kg}\) and a height of \(175\text{ cm}\).
Step 1: Convert height into metres: \(175\text{ cm} = 1.75\text{ m}\).
Step 2: Square the height: \((1.75)^2 = 3.0625\text{ m}^2\).
Step 3: Divide mass by height squared: \(\text{BMI} = \frac{80}{3.0625} \approx 26.12\text{ kg/m}^2\).
Step 4: Classification: Overweight (\(25.0 - 29.9\)).
Common Pitfall: Always convert centimetres to metres before squaring! Dividing \(\text{kg}\) directly by height in \(\text{cm}\) (e.g., \(80 / 175\)) is one of the most common calculation mistakes.
Health Risks of Obesity and Poor Nutrition
• Type 2 Diabetes Mellitus: Prolonged positive energy balance and excess adiposity lead to insulin resistance in body tissues.
• Cardiovascular Disease (CVD): Contributes to the development of atherosclerosis (narrowing of arteries), hypertension (high blood pressure), coronary heart disease, and strokes.
• Osteoarthritis: Excess body mass places heightened mechanical load on weight-bearing joints (such as the knees and hips), causing cartilage degradation.
4. Alcohol and Health Consequences
Alcohol is a significant dietary factor that affects multiple organ systems and carries a high calorific value, contributing directly to a positive energy balance.
• Liver Damage: Chronic alcohol intake leads to progressive liver disease: alcoholic fatty liver \(\rightarrow\) alcoholic hepatitis \(\rightarrow\) cirrhosis (irreversible scarring of liver tissue).
• Cardiovascular System: Results in sustained elevated blood pressure (hypertension), cardiac arrhythmias (irregular heartbeats), and cardiomyopathy (disease of the heart muscle).
• Nervous System: Causes impaired cognitive processing, long-term neurological degeneration, and peripheral neuropathy (damage to peripheral nerves).
• Energy Balance: Alcohol has a high calorific density, accelerating weight gain and obesity when consumed in excess.
5. Physical Exercise: Immediate Responses vs Long-Term Adaptations
A crucial distinction in your examination is the difference between acute (immediate) responses during a single workout and chronic (long-term) physiological adaptations that develop after weeks of regular training.
A. Immediate (Acute) Physiological Responses to Exercise
When you begin exercising, your muscles immediately demand more oxygen and glucose:
• Cardiac Output (\(CO\)) Increases: Both heart rate (\(HR\)) and stroke volume (\(SV\)) increase.
\(\text{Cardiac Output} = \text{Heart Rate} \times \text{Stroke Volume}\) (\(CO = HR \times SV\)).
Definitions: Stroke Volume is the volume of blood pumped out of the left ventricle per beat. Cardiac Output is the total volume of blood pumped per minute.
• Ventilation Increases: The rate and depth of breathing increase (elevating minute ventilation) to enhance oxygen uptake and carbon dioxide removal.
• Vascular Shunt Mechanism: Arterioles supplying active skeletal muscles vasodilate (widen), while arterioles supplying non-essential organs (like the digestive tract and kidneys) vasoconstrict (narrow), redistributing blood flow to where it is needed most.
B. Long-Term (Chronic) Physiological Adaptations to Regular Aerobic Training
After consistent aerobic training over weeks and months, the body undergoes structural and functional adaptations:
1. Cardiovascular Adaptations:
• Cardiac Hypertrophy: The heart muscle thickens and strengthens, particularly the wall of the left ventricle.
• Increased Stroke Volume: The heart pumps more blood per beat, both at rest and during maximal exercise.
• Resting Bradycardia: Resting heart rate decreases (often below \(60\text{ bpm}\)) because the larger stroke volume can supply the same resting cardiac output with fewer beats.
• Lower Resting Blood Pressure: Blood vessels become healthier and more compliant.
• Increased Capillary Density: Greater network of capillaries forms around skeletal muscle fibres, speeding up gas and nutrient exchange.
2. Respiratory Adaptations:
• Increased Vital Capacity: Greater maximum volume of air exhaled after maximal inhalation.
• Enhanced Gas Exchange Efficiency: Better match between alveolar ventilation and pulmonary capillary perfusion.
3. Musculoskeletal and Metabolic Adaptations:
• Increased Mitochondrial Density: Muscle cells build more mitochondria to generate ATP aerobically.
• Increased Aerobic Enzyme Capacity: Cellular enzymes that drive aerobic respiration become more abundant and active.
• Improved Insulin Sensitivity: Muscle cells take up glucose more effectively, reducing the risk of Type 2 diabetes.
• Increased Bone Mineral Density: Weight-bearing exercise stimulates bone remodelling, protecting against osteoporosis.
Quick Summary Checklist
Before sitting your assessment, make sure you can:
• State the functions and dietary sources of Vitamin C, Vitamin D, Calcium, and Iron.
• Identify the deficiency disorders: Scurvy, Rickets/Osteomalacia, and Iron-deficiency anaemia.
• Calculate BMI using \(\text{BMI} = \frac{\text{kg}}{\text{m}^2}\) and classify values accurately into Underweight, Normal, Overweight, or Obese categories.
• Explain the health risks of obesity (Type 2 diabetes, CVD, osteoarthritis).
• Describe the progression of alcohol-induced liver damage (fatty liver \(\rightarrow\) hepatitis \(\rightarrow\) cirrhosis).
• State the equation \(CO = HR \times SV\) and clearly distinguish between acute responses (e.g. tachycardia, vascular shunt) and chronic adaptations (e.g. cardiac hypertrophy, resting bradycardia, increased mitochondrial density).