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Where does energy come from?

A boy wearing a helmet and gloves in a racing wheelchair

Food and drinks, except water, act as ‘fuel’ for the body because they provide energy.

We need energy for everything we do.

We need energy to function, for example, to keep our heart beating, to breathe, grow, blink and think.

We also need energy to be active, for example, to move, play, run and do sports.

A boy wearing a helmet and gloves in a racing wheelchair
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How much energy is in our food?

Energy from food and drinks is measured in .

Another unit we can use to measure energy in is . People often shorten kilocalories to ‘calories’.

Kilojoules is the metric measurement for energy. Other metric units of measurement are centimetres, metres and kilometres.

Kilocalories is the imperial measurement. Other imperial units of measurement are inches, feet and miles.

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Food labels

A food label usually shows the amount of energy in a food.

The energy information is shown per 100g of a food. Using per 100g makes it easier to compare the amount of energy in different foods.

Some food labels also show how much energy is in a serving. The serving is the amount of the food we are recommended to eat.

Here is a food label for wholemeal bread. The label shows the amount of energy in 100g of bread and in one slice of bread.

It also shows the amount of fat, carbohydrate, fibre and protein in 100g and one slice of the bread.

An illustration of a loaf of bread in a transparent bag with an image of wheat and a food label containing nutritional information
Image caption,
A food label showing the amount of energy, fat, carbohydrate, fibre and protein in wholemeal bread
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Which food provides the most energy?

This slideshow shows the energy in kilojoules for 100g of different foods.

Can you spot which type of food provides the most energy per 100g?

Image gallerySkip image gallerySlide 1 of 3, Spaghetti noodles on a white background, Cooked spaghetti Cooked spaghetti provides 696 kJ of energy per 100g.
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Energy in food

A bar of milk chocolate
Image caption,
Foods like chocolate are high in energy, so they should be eaten in small amounts.

Some foods are higher in energy than other foods.

For example, foods that contain fat are usually 'high' in energy. These include oil, butter, nuts and chocolate.

Fruit and vegetables are usually 'low' in energy.

We need to eat a smaller amount of foods that are high in energy.

This is to make sure that the rest of our energy, and all the different that we need, can come from a variety of other foods.

To find out more about nutrients, take a look at What are nutrients?

A bar of milk chocolate
Image caption,
Foods like chocolate are high in energy, so they should be eaten in small amounts.
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How serving size affects energy

Cubes of butter in a small white dish
Image caption,
100g of butter provides 3,062 kJ of energy.

It is useful to look at the energy in 100g of different foods to help us to compare them, but we don’t eat 100g of all foods.

If we have a smaller or larger amount of a food, the energy it provides changes.

For example, 100g of butter provides 3,062 kJ of energy. However, a serving of butter is around 10g.

10g of butter provides 306 kJ of energy.

Cubes of butter in a small white dish
Image caption,
100g of butter provides 3,062 kJ of energy.
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How much energy do we need?

Different people need different amounts of energy.

The amount of energy someone needs each day depends on their age, if they are male or female and how active they are.

An illustrated baby boy with text underneath saying one year old baby boy needs three thousand two hundred kj per pay, a 10 year old boy with text underneath saying ten year old boy needs eight thousand five hundred kj per day, and an eighteen year man with text underneath saying eighteen year old man needs thirteen two hundred kj per day
Image caption,
These are the approximate amounts of energy needed for an average male person at different ages.
An illustrated baby girl with text underneath saying one year old baby girl needs three thousand kj per pay, a 10 year old girl with text underneath saying ten year old boy needs eight thousand one hundred kj per day, and an eighteen year woman with text underneath saying eighteen year old man needs ten thousand three hundred and one kj per day
Image caption,
These are the approximate amounts of energy needed for an average female person at different ages.
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Energy and activities

Different activities use different amounts of energy.

Here are some examples of the amount of energy a child in primary school would roughly use doing different activities for 15 minutes.

Image gallerySkip image gallerySlide 1 of 4, A child swimming, wearing a turquoise swimming suit and dark blue swimming cap, Swimming Swimming uses around 357 kJ.
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Key words

Kilojoules (kJ) Kilojoules are a metric measurement of energy.
Kilocalories (kcal) Kilocalories are an imperial measurement of energy.
Nutrients Nutrients are substances found in food that carry out certain jobs in the body.
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Quiz: Which food provides the most energy?

Can you find the foods that provide the most energy? Have a go at this quiz to find out.

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More on Cooking and nutrition

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