Where does the energy in food come from, what affects how much we need, and what is energy balance?
Energy in the diet: the energy values of macronutrients, basal metabolic rate and physical activity level, factors affecting energy needs, energy balance, and the effects of taking in too much or too little energy.
A focused answer to the WJEC Food Preparation and Nutrition diet and good health topic on energy, covering the energy values of macronutrients, basal metabolic rate and physical activity, factors affecting energy needs, energy balance, and the effects of too much or too little energy.
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What this dot point is asking
You need to know where the energy in food comes from, the energy values of the macronutrients, what basal metabolic rate and physical activity level mean, the factors that affect energy needs, what energy balance is, and the effects of an imbalance.
Where the energy in food comes from
Energy is measured in kilocalories (kcal) or kilojoules (kJ). It comes from the macronutrients:
- fat: about 9 kcal per gram (the most energy-dense),
- carbohydrate: about 4 kcal per gram,
- protein: about 4 kcal per gram (used for energy when spare),
- alcohol: about 7 kcal per gram (not a nutrient, but provides energy).
This is why fatty and sugary foods are easy to overeat in terms of energy.
BMR and physical activity
Your total daily energy need is roughly your BMR plus the energy for activity. BMR is the largest part for most people, which is why even at rest the body uses energy. People with more muscle tend to have a higher BMR, because muscle uses more energy than fat even at rest.
As a rough guide, an average adult woman needs about 2,000 kcal a day and an average adult man about 2,500 kcal a day, but the right amount depends on the factors below. Food labels often show energy as a percentage of the reference intake (RI) for an average adult, which helps people judge how a portion fits into their day.
What affects energy needs
- Age: children and teenagers need a lot for growth; needs fall in older age.
- Sex: males usually need more, as they tend to have more muscle and a higher BMR.
- Body size and muscle: larger, more muscular bodies use more energy.
- Activity level: an active person or manual worker uses far more than someone mostly sitting.
- Pregnancy and breastfeeding: raise a woman's energy needs.
Energy balance
- Energy in more than energy out: the excess is stored as fat, causing weight gain and, over time, obesity.
- Energy in less than energy out: the body uses its fat stores, causing weight loss.
The effects of an imbalance
Too much energy: weight gain and obesity, which raises the risk of type 2 diabetes, heart disease, high blood pressure and some cancers, and strains the joints.
Too little energy: weight loss, and if extreme, tiredness, poor concentration, weakened immunity and, in young people, slowed growth.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style6 marksExplain what is meant by energy balance and describe what happens to the body if a person regularly takes in more energy than they use.Show worked answer →
A 6-mark question. Mark it for a clear definition of energy balance plus the consequences of a positive imbalance.
Energy balance means the energy taken in from food and drink equals the energy used by the body for its basal metabolic rate and physical activity. When energy in equals energy out, body weight stays the same. If a person regularly takes in more energy than they use, the extra energy is stored as fat, so they gain weight over time. Continued weight gain leads to becoming overweight and then obese, which raises the risk of type 2 diabetes, heart disease, high blood pressure and some cancers, and puts strain on joints.
A top answer defines energy balance, states that excess energy is stored as fat causing weight gain, and links obesity to named health risks. Reward the precise idea of energy in versus energy out.
WJEC style4 marksDescribe four factors that affect how much energy a person needs each day.Show worked answer →
A 4-mark question. Award one mark per correct factor.
Age affects energy needs: children and teenagers need a lot for growth, and needs fall in older age. Activity level matters: an active person or manual worker uses more energy than someone who sits most of the day. Sex affects it: males usually need more than females because they tend to have more muscle and a higher basal metabolic rate. Body size and amount of muscle increase needs, and pregnancy and breastfeeding raise a woman's energy needs.
Markers reward any four of: age, activity level, sex, body size or muscle, and pregnancy/breastfeeding, each correctly linked to energy needs.
Related dot points
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Sources & how we know this
- WJEC Eduqas GCSE Food Preparation and Nutrition specification (from 2016) — WJEC Eduqas (2016)