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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.
| 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 |
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 |
| 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.
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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