Welcome to Nutrition and Physical Exercise in Maintaining Good Health
Welcome to one of the most practical and fascinating topics in your CCEA AS 2: Human Body Systems unit! In this chapter, we will explore how the fuel we put into our bodies (nutrition) and the way we move (exercise) work together to keep us healthy and prevent disease.
Whether you find biology a breeze or you are working hard to grasp the basics, do not worry—we will break down every concept, formula, and adaptation step by step so that you feel fully confident for your exam.
---1. Energy Balance and Basal Metabolic Rate (BMR)
What is Energy Balance?
Think of your body like a biological bank account. You deposit energy when you eat and drink, and you withdraw energy when your body works and moves.
Energy Balance is achieved when:
Energy Intake = Total Energy Expenditure
• Energy Intake: The calories (energy) you consume from macronutrients—specifically carbohydrates, lipids (fats), and proteins.
• Total Energy Expenditure: The sum of your Basal Metabolic Rate (BMR), energy used during physical activity, and diet-induced thermogenesis (the energy required to digest and process food).
If intake is greater than expenditure, excess energy is stored as adipose tissue (weight gain). If expenditure is greater than intake, the body mobilises stored energy (weight loss).
Understanding Basal Metabolic Rate (BMR)
Basal Metabolic Rate (BMR) is the minimum amount of energy required to sustain vital bodily functions at complete physical and mental rest in a thermoneutral environment.
Even when you are lying completely still and asleep, your body is hard at work carrying out vital processes such as:
• Cellular maintenance and active transport
• Respiration and gas exchange
• Circulation of blood by the heart
Factors That Influence BMR
Why do different people have different baseline energy needs? Three main factors determine a person's BMR:
1. Age:
BMR decreases as a person gets older. This is primarily due to a natural, gradual loss of lean muscle mass with advancing age.
2. Biological Sex:
Biological males generally have a higher BMR than biological females. This is because males typically have a higher proportion of lean muscle mass relative to adipose tissue.
3. Body Composition and Mass:
Muscle tissue is far more metabolically active than fat (adipose) tissue. Therefore, an individual with a greater amount of lean muscle mass will burn more energy at rest, resulting in a higher BMR.
Quick Review & Common Pitfall:
Exam Tip: Never confuse BMR with total daily energy expenditure! BMR is strictly the baseline energy needed at rest to keep your organs functioning—it does not include the energy you burn while walking, studying, or exercising.
2. Dietary Requirements Across Specific Population Groups
Human nutritional requirements are not "one size fits all." As we progress through life stages or undergo major physiological changes, our nutritional priorities shift.
A. Children and Adolescents
• High Energy Density: Children and teenagers need high energy intake relative to their body mass to fuel rapid somatic growth, tissue development, and high daily physical activity.
• Protein: Essential for the structural growth and repair of new tissues.
• Calcium and Vitamin D: Crucial for osteogenesis (bone formation), skeletal lengthening, and bone mineralisation during growth spurts.
• Iron: Vital for supporting the expansion of total blood volume (forming haemoglobin in red blood cells) and building muscle tissue (synthesising myoglobin).
B. Pregnant and Lactating Women
• Increased Caloric Intake: Extra energy is needed to support fetal growth and placenta development, particularly during the third trimester and while producing breast milk during lactation.
• Folic Acid (Vitamin B9): Crucial prior to conception and in early pregnancy to prevent Neural Tube Defects (NTDs), such as spina bifida.
• Iron: Essential to prevent maternal anaemia, support the expansion of the maternal blood supply, and facilitate fetal red blood cell development and placental growth.
• Calcium: Transferred across the placenta to build the developing fetal skeleton without depleting the mother's own bone reserves.
C. Older Adults (The Elderly)
• Lower Energy Intake: Total energy requirements decrease due to a reduced BMR (caused by muscle loss) and lower levels of physical activity.
• Calcium and Vitamin D: Vital to slow down bone demineralisation and help protect against conditions like osteopenia and osteoporosis (brittle bones).
• Dietary Fibre (Roughage): Essential for stimulating intestinal peristalsis to combat age-related digestive sluggishness and prevent constipation.
• Hydration & Micronutrient Density: Older adults require nutrient-dense meals with adequate fluids to avoid malnutrition and dehydration without consuming excess fats or refined sugars.
Key Takeaway:
Remember: Proteins build and repair tissue; Calcium and Vitamin D build and protect bones; Iron supports oxygen transport in blood and muscle; Folic acid protects the fetal neural tube.
3. Health Assessment Metrics and Thresholds
Healthcare professionals use non-invasive, anthropometric measurements to evaluate an individual's body composition and assess their risk of cardiovascular and metabolic diseases.
1. Body Mass Index (BMI)
BMI is a widely used screening tool that assesses body weight relative to height.
The Formula:
\(\text{BMI} = \frac{\text{Weight in kilograms}}{(\text{Height in metres})^2}\)
Units: \(\text{kg/m}^2\)
Standard CCEA / WHO Classifications:
• Underweight: \(< 18.5\text{ kg/m}^2\)
• Normal weight: \(18.5 - 24.9\text{ kg/m}^2\)
• Overweight: \(25.0 - 29.9\text{ kg/m}^2\)
• Obese (Class I): \(30.0 - 34.9\text{ kg/m}^2\)
• Obese (Class II / III): \(\ge 35.0\text{ kg/m}^2\)
Step-by-Step Calculation Example:
Problem: A person weighs \(72\text{ kg}\) and has a height of \(175\text{ cm}\). Calculate their BMI and state their category.
Step 1: Convert height to metres \(\implies 175\text{ cm} = 1.75\text{ m}\).
Step 2: Square the height \(\implies 1.75 \times 1.75 = 3.0625\text{ m}^2\).
Step 3: Divide weight by height squared \(\implies \frac{72}{3.0625} \approx 23.51\text{ kg/m}^2\).
Classification: Normal weight (as \(23.51\) falls between \(18.5\) and \(24.9\)).
Common Mistake to Avoid:
Do not forget to convert centimetres into metres before squaring! If you divide by \(175^2\), your answer will be incorrect.
2. Waist-to-Hip Ratio (WHR)
While BMI measures overall mass, it does not show where fat is stored. The Waist-to-Hip Ratio (WHR) assesses central (abdominal/visceral) adiposity—fat stored around internal organs in the abdomen, which is a major risk factor for chronic diseases.
The Formula:
\(\text{WHR} = \frac{\text{Waist circumference (cm)}}{\text{Hip circumference (cm)}}\)
Risk Thresholds:
A higher WHR indicates increased risk of cardiovascular disease and metabolic disorders (such as Type 2 diabetes):
• Females: \(\text{WHR} > 0.85\) indicates increased health risk.
• Males: \(\text{WHR} > 0.90\) indicates increased health risk.
4. Physiological Adaptations to Regular Physical Exercise
When you take part in regular exercise training, your body undergoes systematic adaptations that improve efficiency and lower the risk of chronic disease.
A. Cardiovascular Adaptations
1. Cardiac Hypertrophy & Increased Stroke Volume:
Regular endurance training causes hypertrophy (strengthening and enlargement) of the cardiac muscle, especially the left ventricle wall. This allows the heart to pump more blood with each contraction, resulting in an increased Stroke Volume (SV) at rest and during exercise.
2. Decreased Resting Heart Rate (Resting Bradycardia):
Cardiac output (\(Q\)) is the volume of blood pumped by the heart per minute, calculated as:
\(\text{Cardiac Output } (Q) = \text{Stroke Volume } (SV) \times \text{Heart Rate } (HR)\)
Because a trained athlete's heart has a significantly larger Stroke Volume (\(SV\)), it can maintain the required resting Cardiac Output (\(Q\)) with fewer beats per minute. This results in a lower resting heart rate (bradycardia).
3. Increased Capillary Density:
Exercise stimulates the formation of new capillaries around skeletal muscle fibres and within the myocardium (heart muscle). This increases the surface area for gas exchange and shortens the diffusion distance, dramatically improving oxygen delivery and carbon dioxide removal.
4. Lower Resting Blood Pressure:
Long-term exercise leads to reduced vascular resistance, lowering both resting systolic and diastolic arterial blood pressures.
B. Metabolic and Blood Lipid Profile Adaptations
1. Improved Blood Lipid Profile:
• Increases High-Density Lipoproteins (HDL): Known as "good cholesterol," HDL transports cholesterol away from artery walls back to the liver for excretion.
• Decreases Low-Density Lipoproteins (LDL) and Triglycerides: LDL carries cholesterol to tissues; high levels lead to fatty plaques in artery walls. Lowering LDL and triglycerides reduces the risk of atherosclerosis (narrowing of the arteries).
2. Enhanced Glucose Regulation and Insulin Sensitivity:
• Regular muscular contractions increase the expression and translocation of GLUT4 glucose transporter proteins in skeletal muscle cell membranes.
• This increases insulin sensitivity, allowing muscle cells to take up glucose efficiently from the bloodstream and significantly lowering the risk of developing Type 2 Diabetes Mellitus.
Summary: Key Takeaways for Your Exam
• Energy Balance: Energy Intake = Total Expenditure (BMR + activity + thermogenesis).
• BMR: Minimum energy to sustain vital life functions at complete physical and mental rest.
• Dietary Needs: Folic acid prevents neural tube defects in pregnancy; Calcium/Vitamin D supports bone health in youth and prevents osteoporosis in older age; Iron is vital for expanding blood volume and muscle tissue.
• Metrics: \(\text{BMI} = \frac{\text{Weight (kg)}}{(\text{Height (m)})^2}\). WHR measures central adiposity (thresholds: \(> 0.85\) for females, \(> 0.90\) for males).
• Exercise Benefits: Cardiac hypertrophy \(\implies \uparrow \text{Stroke Volume} \implies \downarrow \text{Resting Heart Rate}\) (\(Q = SV \times HR\)); \(\uparrow \text{Capillary density}\); \(\uparrow \text{HDL}\) and \(\downarrow \text{LDL}\); \(\uparrow \text{GLUT4 expression}\) (lowering Type 2 Diabetes risk).