• Healthy eating, healthy living
• The balancing act: energy in and out
  • Energy ups and downs
  • Energy from food
  • Energy in, energy out
  • Make a meal of it
  • Design a better breakfast
• Growing our grain: the science of farming
• Following the 'grain chain': from field to fork
• The farming business: today and tomorrow
• Making and baking: the science and technology
• Food for fun: making and celebrating

ENERGY IN, ENERGY OUT

The body needs energy from food and drink to work properly and stay healthy.

Energy input and output

• The amount of energy the body gets from what a person eats is the energy input.
• The amount of energy the body uses up is the energy output.

The more food a person eats, the larger the input; the more active they are, the bigger the output. It is important the energy input and output is kept in balance.

If too little is eaten, there will be a negative energy balance – that means the body has taken in too little food to provide the energy it needs. The person may lose weight because the body uses up its fat reserves to provide the extra energy.

If too much is eaten, the person will have a positive energy balance – this means that they have eaten more than they need for the energy their body is using. Because they are not using up all the food they eat, they may put on weight.

Keeping your energy input and output in balance is not always easy. Most people are not active enough. But being active doesn't mean you have to be very sporty or enjoy the latest fitness fad – simple activities like walking instead of going in the car, climbing stairs instead of taking a lift or escalator, or helping to mow the lawn or do the housework are all ways of being active and keeping your input and output balanced.

Measuring energy

The energy provided by a food or a drink is usually measured in calories (or joules).

1 calorie = 4.2kJ (kilojoules)

Scientists find out how much energy there is in a particular food by burning a sample of it and measuring how much heat energy is released. The process is called calorimetry.

This chart shows the average energy used in 15 minutes by a child weighing 35kg (5½ stone) and doing different activities.

Calories in food

Food and drink provide the calories needed by the body. The table shows the average amount of calories in some common foods. The actual number depends on the size of the portion – you can check the labels on different foods to see exactly how many calories they contain. But remember that the type of food you eat is important too, to give you all the nutrients you need (see the Healthy eating, healthy living section).

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