What causes obesity, how is it measured, and how can diet and lifestyle manage it?
Obesity and weight management: the causes and measurement of overweight and obesity (BMI and energy imbalance), the health consequences, the role of diet, physical activity and lifestyle, and current research and strategies for prevention and management.
A CCEA A-Level Nutrition and Food Science answer on obesity and weight management: the causes and measurement of obesity (BMI and energy imbalance), its health consequences, the role of diet, activity and lifestyle, and current research and strategies for prevention and management.
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What this dot point is asking
CCEA wants you to explain what causes overweight and obesity, how they are measured (BMI and energy imbalance), the health consequences, and the roles of diet, physical activity and lifestyle in preventing and managing obesity, drawing on current research and strategy.
Causes and measurement
The most common measure is body mass index (BMI):
A BMI under 18.5 is underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, and 30 or above obese. BMI is quick and useful for populations, but it does not distinguish fat from muscle (a muscular athlete may score high) or show where fat is stored, so waist measurement is sometimes used alongside it because abdominal fat carries the most risk.
Consequences and management
Current research stresses that obesity is driven by the food environment as much as by individual choice, so strategy combines personal advice with population measures such as reformulation, the soft-drinks levy, marketing restrictions and active-travel schemes. CCEA expects you to evaluate both individual and societal approaches.
Examples in context
Example 1. Portion size creep. A family whose plates, takeaways and sugary drinks have all grown larger gradually takes in more energy than they use, slowly gaining weight. Returning to sensible portions, swapping sugary drinks for water, and adding a daily walk restores energy balance without extreme dieting. This shows obesity as a cumulative energy-balance problem and a manageable one.
Example 2. Obesity and type 2 diabetes. Excess abdominal fat makes the body's cells less responsive to insulin, so obesity is the leading risk factor for type 2 diabetes. A person who loses weight through diet and activity can improve their blood-glucose control and, in some cases, push early type 2 diabetes into remission. This links obesity directly to the disease content of the unit.
Try this
Q1. State the formula for body mass index and the BMI value at which a person is classified as obese. [2 marks]
- Cue. BMI = mass in kg divided by height in metres squared; obese is a BMI of 30 or above.
Q2. Explain, in terms of energy, why obesity develops. [2 marks]
- Cue. Energy intake exceeds energy output over a long period, so the surplus is stored as fat.
Q3. Name three health risks associated with obesity. [3 marks]
- Cue. Any three of: type 2 diabetes, coronary heart disease, high blood pressure, some cancers, osteoarthritis.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA AS 20186 marksDiscuss the dietary and lifestyle factors that contribute to obesity, and explain the health risks associated with being obese.Show worked answer →
A 6-mark answer needs the causes (an energy surplus and the behaviours behind it) and the named health risks.
Obesity results from a long-term positive energy balance, in which energy intake exceeds energy output, so the surplus is stored as fat. Dietary factors include large portion sizes, frequent consumption of energy-dense foods high in fat and free sugars, sugary drinks, and snacking and eating out, all of which raise intake. Lifestyle factors include low levels of physical activity, sedentary screen time, sedentary jobs and transport, which lower output. Wider factors include the easy availability and marketing of cheap, energy-dense food.
The health risks of obesity include type 2 diabetes, coronary heart disease and high blood pressure, certain cancers (such as bowel and breast), joint problems such as osteoarthritis, gallstones, breathing problems and a higher risk of some mental-health difficulties.
Markers reward the energy-balance explanation, at least two dietary and two lifestyle causes, and at least three named health risks.
CCEA AS 20204 marksExplain how body mass index (BMI) is used to classify weight, and state one limitation of the measure.Show worked answer →
A 4-mark answer needs how BMI is calculated and interpreted, plus a valid limitation.
Body mass index is calculated by dividing a person's mass in kilograms by the square of their height in metres. The result is compared with set ranges: roughly under 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25 to 29.9 is overweight, and 30 or above is obese.
A limitation is that BMI does not distinguish fat from muscle, so a very muscular person (such as an athlete) may have a high BMI without excess fat. It also does not show where fat is stored, although abdominal fat carries the most risk, so waist measurement is sometimes used alongside it.
Markers reward the correct calculation, the classification ranges, and one valid limitation such as not separating fat from muscle.
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Sources & how we know this
- CCEA GCE Nutrition and Food Science specification — CCEA (2016)
- Health matters: obesity and the food environment — Public Health England (2017)