We use energy all the time, even when we are asleep.
We need energy for our body to work.
We need energy to keep us warm.
When the weather is cold, or when we take part in sports, we need extra amounts of energy to help our body and muscles work harder.
Our energy comes from the food we eat.
 Food contains chemical energy. As the food is broken down, our body uses the energy to keep warm and to do work.

Do you know which foods contain large amounts of chemical energy?

Scientists have been able to work out the amounts of chemical energy in different foods.
The amount of energy in food is measured in units called calories.
A plateful of lettuce, for example, has few calories and therefore very little energy.
Rice and bananas contain much more energy.
But an equal amount of ice cream contains even more!
When you eat food, it travels through your body to your stomach and intestines.
Special chemicals called enzymes in your stomach break down the food into different substances that your body can use. We call this breaking-down process digestion. The substances from food that produce energy for your body most efficiently are called fats and carbohydrates. Fats, like butter and oil, and carbohydrates, like bread, potatoes, and sugars, are high in calories.

Our body needs energy

Different people need different amounts of energy from their food. A person doing heavy work, like digging or sawing wood, or an Arctic explorer in the freezing cold needs a lot more energy than an office worker. Active children need about the same amount of energy as adults doing light work. Older people usually do less work and move around more slowly, so they need less energy.
It is important to eat only as much food as your body needs to keep your weight and energy at a comfortable level. It is also important to eat the right kinds of food. Besides fats and carbohydrates, your body also needs proteins such as fish, meat, and cheese. Protein is necessary for the growth and maintenance of body structures.