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

Consequence	How Obesity Causes It
Coronary heart disease	Excess fat increases cholesterol; fatty deposits narrow coronary arteries
Type 2 diabetes	Excess fat causes insulin resistance; body cannot regulate blood sugar
Hypertension	Extra body mass increases strain on the heart and blood vessels
Stroke	High blood pressure and cholesterol increase clot and rupture risk
Some cancers	Linked to increased risk of bowel, breast and pancreatic cancer
Osteoarthritis	Excess weight puts strain on joints, especially knees and hips
Sleep apnoea	Fat deposits around the airway cause breathing interruptions during sleep
Depression	Low self-esteem, body image issues, social stigma
Reduced life expectancy	All of the above contribute to premature death

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Effects of Obesity on Sporting Performance

Effect	Detail
Reduced cardiovascular endurance	Excess weight increases oxygen demand; the heart must work harder
Reduced speed and agility	Extra mass makes it harder to accelerate, change direction and move quickly
Reduced flexibility	Excess fat restricts range of movement at joints
Increased injury risk	Greater strain on joints, ligaments and tendons
Overheating	Fat acts as insulation, making it harder to cool down during exercise
Reduced power-to-weight ratio	More weight to move with the same or less muscle force
Breathlessness	Increased oxygen demand leads to faster fatigue

However, in some sports, higher body mass can be an advantage:

• Sumo wrestling — greater mass helps push opponents
• Rugby prop — weight aids scrummaging stability
• Shot put — body mass contributes to throwing force

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Strategies to Prevent and Treat Obesity

Strategy	Detail
Increase physical activity	Shift the energy balance towards negative; burn more calories
Improve diet	Reduce portion sizes, processed foods, sugar and saturated fat; increase fruit, vegetables and whole grains
Education	Teach people about energy balance, nutrition labels and healthy cooking
Government campaigns	Change4Life, sugar tax on soft drinks, calorie labelling on menus
Community provision	Free exercise programmes, Parkrun, accessible leisure facilities
Medical intervention	In severe cases — medication, bariatric surgery, NHS weight management programmes

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The Obesity Epidemic in the UK

Key statistics (approximate):

• Over 25% of UK adults are classified as obese
• Childhood obesity is a particular concern — approximately 1 in 5 children leaving primary school are obese
• Obesity costs the NHS an estimated £6 billion per year
• It is the second leading preventable cause of death (after smoking)

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Common Exam Mistakes

1. Defining obesity as simply "being fat." Use the precise definition: excessive body fat that presents a risk to health, measured by BMI 30+.
2. Not linking obesity to energy balance. Always explain that obesity results from a chronic positive energy balance.
3. Forgetting the limitations of BMI. If the question asks about measuring obesity, discuss both the usefulness and limitations of BMI.
4. Only discussing health consequences. Also cover the effects on sporting performance — the exam often asks about this specifically.

Exam Tip: When a question asks about obesity and performance, structure your answer around specific fitness components: cardiovascular endurance (reduced), speed (reduced), flexibility (reduced), agility (reduced). This demonstrates precise knowledge.

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Summary