Obesity

Obesity is a condition characterised by excessive body fat that presents a risk to health. It is a major public health issue in the UK and a key topic in the Edexcel GCSE PE specification. You must understand its causes, effects on health and performance, how it is measured, and how it links to energy balance.

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Defining Obesity

Term	Definition
Overweight	Having a body weight above the recommended level for height (BMI 25–29.9)
Obese	Having an excessive amount of body fat that presents a serious risk to health (BMI 30+)
Morbidly obese	A severe level of obesity (BMI 40+) with very high health risks
BMI	Body Mass Index — a measure of body fat based on weight relative to height

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Measuring Obesity — BMI

BMI (Body Mass Index) is calculated as:

BMI = Weight (kg) / Height (m)²

BMI Range	Classification
Below 18.5	Underweight
18.5–24.9	Normal weight
25.0–29.9	Overweight
30.0–39.9	Obese
40.0+	Morbidly obese

Limitations of BMI

Limitation	Explanation
Does not distinguish fat from muscle	A muscular athlete (e.g. rugby player) may have a high BMI but low body fat
Does not account for body composition	Two people with the same BMI may have very different fat/muscle ratios
Does not show fat distribution	Abdominal fat is more dangerous than fat on the hips/thighs
Varies by age and sex	BMI ranges are not always accurate for children, older adults or different ethnic groups

Exam Tip: When discussing BMI, always mention at least one limitation. The exam often asks students to evaluate BMI as a measure of obesity. A balanced answer that gives both strengths and limitations will score higher.

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Causes of Obesity

graph TD
    A["Causes of Obesity"] --> B["Positive Energy Balance"]
    A --> C["Sedentary Lifestyle"]
    A --> D["Poor Diet"]
    A --> E["Genetics"]
    A --> F["Medical Conditions"]
    A --> G["Psychological Factors"]
    B --> H["Energy In > Energy Out"]
    C --> H
    D --> H
    style A fill:#e53935,color:#fff
    style H fill:#ffcdd2,stroke:#c62828

Cause	Detail
Positive energy balance	The fundamental cause — consuming more energy than the body expends
Sedentary lifestyle	Physical inactivity reduces energy expenditure
Poor diet	High intake of processed foods, sugary drinks, saturated fats and large portion sizes
Genetics	Some people are genetically predisposed to store fat more easily
Medical conditions	Hypothyroidism, Cushing's syndrome and some medications can promote weight gain
Psychological factors	Emotional eating, stress eating, comfort eating
Environmental factors	Availability of fast food, "food deserts" with limited access to fresh produce

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Health Consequences of Obesity