Where does food energy come from, and what decides how much we need?
Energy from food measured in kilocalories and kilojoules, the energy values of macronutrients, energy balance, basal metabolic rate (BMR) and physical activity level, and the factors that affect energy needs.
A focused CCEA GCSE Food and Nutrition answer on energy, covering kilocalories and kilojoules, the energy values of carbohydrate, fat and protein, energy balance, basal metabolic rate and physical activity level, and the factors affecting energy needs.
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What this dot point is asking
CCEA wants you to know how food energy is measured, how much energy each macronutrient gives, what energy balance means, what basal metabolic rate and physical activity level are, and what factors change how much energy a person needs.
Measuring food energy
Energy values of the macronutrients
| Nutrient | Energy per gram |
|---|---|
| Fat | About 9 kcal |
| Carbohydrate | About 4 kcal |
| Protein | About 4 kcal |
| Alcohol | About 7 kcal |
Energy balance
If intake is greater than output, the extra energy is stored as body fat, leading to weight gain and, over time, obesity. If intake is less than output, the body uses its fat stores, leading to weight loss.
BMR and physical activity level
Total daily energy need is roughly BMR plus the energy used in activity, so an active person needs more than someone who sits still all day.
Factors affecting energy needs
Energy needs change with age (growing children and teenagers need a lot for their size; needs fall in older age), activity level (a manual worker or athlete needs more than someone sedentary), body size and gender (larger people and often males have a higher BMR), and life stage (pregnancy and breastfeeding raise needs).
Why energy balance matters
Long-term positive energy balance (too much intake) is the main dietary cause of obesity, which raises the risk of heart disease, type 2 diabetes and joint problems. Long-term negative balance causes underweight, tiredness and loss of muscle. Matching intake to needs is the heart of a healthy diet.
Examples in context
- Example 1. Why fat is the first target when slimming
- Because fat provides about 9 kcal per gram, swapping fried for grilled food, or full-fat for lower-fat dairy, removes a lot of energy for a small change. This applies the macronutrient energy values to a real weight-control decision.
- Example 2. Reading energy on a label
- Nutrition labels show energy per 100 g and per portion in both kcal and kJ. Comparing the kcal per portion of two ready meals helps a shopper pick the lower-energy option, linking energy to food labelling.
- Example 3. Higher needs in pregnancy and breastfeeding
- A breastfeeding mother needs extra energy to produce milk, so her requirement rises above her normal level. This shows a life stage raising energy needs, a common CCEA link between energy and dietary needs through life.
Try this
Q1. State how much energy fat provides per gram, and how this compares with carbohydrate. [2 marks]
- Cue. Fat about 9 kcal per gram; carbohydrate about 4 kcal per gram, so fat gives more than twice as much.
Q2. Explain what happens to body weight if energy intake is regularly greater than energy output. [2 marks]
- Cue. The extra energy is stored as body fat, so weight increases and can lead to obesity.
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 past-style6 marksExplain what is meant by energy balance, and describe what happens to the body when energy intake is greater than, and less than, energy output.Show worked answer →
Six marks: define energy balance and explain both imbalances.
Energy balance is the state where the energy taken in from food and drink equals the energy used by the body. When they are equal, body weight stays the same.
If energy intake is greater than energy output, the extra energy is stored as body fat. Over time this leads to weight gain and, if it continues, to overweight and obesity, with raised risk of heart disease and type 2 diabetes.
If energy intake is less than energy output, the body uses up its fat stores to make up the difference, leading to weight loss. If this goes too far it causes underweight, tiredness and loss of muscle.
Markers reward a clear definition and a correct outcome for each imbalance.
CCEA past-style4 marksDefine basal metabolic rate and state three factors that affect a person's energy needs.Show worked answer →
Four marks: definition plus three factors.
Basal metabolic rate (BMR) is the amount of energy the body needs at complete rest just to keep its essential processes going, such as breathing, heartbeat and keeping warm.
Factors affecting energy needs: age (children and teenagers growing need more relative to size; needs fall in older age); activity level (an active or manual worker needs more than someone sedentary); body size and gender (larger people and often males have a higher BMR); whether someone is pregnant or breastfeeding (needs rise); occupation.
Markers accept any three valid factors plus the BMR definition.
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