Food as fuel

All the energy we need comes from our food and drink.

What is the Basal Metabolic Rate (BMR)?

About half of the energy we get from our food is used for things like:

  • growing
  • healing
  • regulating our body’s temperature

These are all know as bodily functions and are measured using a Basal Metabolic Rate (BMR).

BMR is the measurement of the energy the body requires to function when it is resting. Our bodies are amazing. Even when we are physically still, our bodies are busy on the inside and this requires energy. Everyone’s BMR is at a slightly different rate because we are all unique.

Find out more about our body systems with 2nd level Science.

Physical activity

The rest of the energy is used for physical activities. These range from:

  • very energetic ones like walking, dancing, running and playing football
  • to less energetic activities like tidying up your bedroom, watching television and even sleeping

We can work out how much energy our food is giving us by looking at nutrition labels. We measure energy in calories. To find out how much energy food provide, look for kcal or cal on packaging.

The more active you are the more calories you need to consume to keep up your energy levels. Every day we need to eat and drink to replace the energy we have used.

Imagine a car...

...the more petrol in the tank the further it can drive. Our bodies are no different. We can’t expect to have energy if we are not eating a healthy balanced diet to fuel them.

What do we need energy for?

Child walking to school in uniform

Walking to school

Our bodies need fuel to walk to and from school so it's important we eat a healthy varied diet to help power those steps.

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Food choices

Some foods release energy slowly and others release energy quickly.

Complex carbohydrates

Slow releasing energy foods are called complex carbohydrates.

  • Complex carbohydrates, also known as starch, can be found in bread, pasta, flour and rice.
  • The wholemeal varieties of these are the healthiest for us because they contain more fibre and less sugar.
  • Complex carbohydrates also include vegetables such as sweet potato, spinach and parsnips.
  • Complex carbohydrates release energy slowly and take time to digest which help us feel fuller for longer.
Complex carbohydrates release energy slowly. They take longer to digest so they help make you feel fuller for longer.

Simple carbohydrates

Fast releasing energy foods are known as simple carbohydrates.

  • Simple carbohydrates release their calories very quickly.
  • Simple carbohydrates are foods high in sugar.
  • Foods like chocolate, biscuits, fizzy drinks and some fruits give us a quick burst of energy but can then leave us feeling tired and hungry.
  • They can also have an unhealthy impact on our blood sugar levels leaving us feeling overly tired.
  • Although some fruits, like grapes or bananas, are full of natural sugars, they are also full of vitamins, minerals and fibre unlike sweeties.
Simple carbohydrates are foods high in sugar, like chocolate, biscuits, fizzy drinks and some fruits.

Try the quiz below. Can you work out the difference between slow releasing and fast releasing energy foods?


  • Choose three foods you can find in your kitchen.
  • Imagine you were running a race.
  • Which out of the three foods would give you the most energy to run the race?
  • Remember you will need slow releasing energy to finish the race.

There's more to learn...