Study Notes
Overview
This topic explores the fundamental principles of energy balance, a cornerstone of nutritional science. For the OCR GCSE exam, candidates are expected to demonstrate a precise understanding of the relationship between energy intake (the food we consume) and energy expenditure (the energy our bodies use). This includes defining Basal Metabolic Rate (BMR) and Physical Activity Level (PAL), and explaining how their interplay determines whether an individual gains, loses, or maintains weight. Examiners will award marks for the ability to apply this knowledge to real-world scenarios, calculate energy requirements, and analyse the health consequences of long-term energy imbalance. Mastery of this area is crucial, as it not only forms the basis of many exam questions but also connects to broader topics such as macronutrients, diet-related health conditions, and menu planning.
Key Concepts
The Three States of Energy Balance
What it is: Energy balance is the relationship between the energy consumed from food and drink (intake) and the energy used by the body for basic functions and physical activity (expenditure). It can be in one of three states.
Why it matters: This is the core concept. Questions will require you to identify and explain these states in different contexts.
Specific Knowledge:
- Positive Energy Balance: Intake > Expenditure. Leads to weight gain as excess energy is stored as adipose tissue.
- Energy Balance: Intake = Expenditure. Leads to stable weight.
- Negative Energy Balance: Intake < Expenditure. Leads to weight loss as the body uses stored adipose tissue for energy.
Basal Metabolic Rate (BMR) & Physical Activity Level (PAL)
What they are:
- BMR: The minimum amount of energy the body needs to function at rest. This includes processes like breathing, circulation, and cell repair. It accounts for 60-75% of total energy expenditure.
- PAL: The energy used during physical movement. It is expressed as a multiplier to calculate total energy needs.
Why they matter: These two components make up total energy expenditure. You must be able to define them and explain the factors that affect them.
Specific Knowledge:
- Factors affecting BMR: Age (decreases with age), Gender (males generally higher), Body Size & Composition (more muscle = higher BMR).
- PAL Values: Sedentary (e.g., office worker) ≈ 1.4, Moderately Active (e.g., regular walking) ≈ 1.6, Vigorous (e.g., athlete) ≈ 1.9.
- The Formula: Total Energy Requirement = BMR × PAL. You must know and be able to use this formula.
Macronutrient Energy Values (Atwater Factors)
What they are: The amount of energy (in kilocalories) provided per gram of each macronutrient.
Why it matters: These values are essential for any calculation question involving the energy content of food. They also explain why some foods are more 'energy-dense' than others.
Specific Knowledge:
- Fat: 9 kcal/g
- Protein: 4 kcal/g
- Carbohydrate: 4 kcal/g
- Alcohol: 7 kcal/g (often included in questions)
Second-Order Concepts
Causation
- Cause of Weight Gain: A sustained positive energy balance, where energy intake consistently exceeds expenditure. This is often caused by a combination of consuming energy-dense foods high in fat and free sugars, and a low Physical Activity Level (sedentary lifestyle).
- Cause of Weight Loss: A sustained negative energy balance. This is achieved by reducing energy intake, increasing energy expenditure, or a combination of both.
Consequence
- Consequences of Positive Energy Balance: Long-term positive energy balance leads to obesity. This significantly increases the risk of developing diet-related health conditions, most notably Type 2 diabetes and Coronary Heart Disease (CHD). Credit is given for naming these specific conditions.
- Consequences of Negative Energy Balance: While often intentional for weight management, a severe or prolonged negative energy balance can lead to malnutrition, muscle loss, and nutrient deficiencies.