Balancing energy in and out

Balancing energy in and out

What are kilojoules (kj) or calories?

Energy is measured in kilojoules (kj) or calories, so when we refer to ‘energy in’ we actually mean ‘kilojoules in’ (the kilojoules in the food we have eaten).

Maintaining a healthy weight range is important for minimising the risk of many lifestyle diseases such as heart disease, some cancers and type 2 diabetes.

The best way to maintain a healthy weight is to match the energy you consume from food with the energy that your body uses up.

Energy in = Energy out
To maintain body weight you need to aim for your energy intake to equal your energy output. The amount of energy an individual requires each day depends on how active that person is, and whether or not the body is still growing (i.e. children and adolescents).

The table below is a guide to the estimated daily energy requirements for an ‘average’ person with low level of physical activity, eg sedentary work such as office work, and no strenuous exercise.

Actual energy needs for individuals will vary considerably depending on activity levels, body composition, state of health, age, weight and height.

Estimated daily energy requirement (kilojoules) for a sedentary person
(eg office work or study, no strenuous physical activity)




12-15 years 8200-9900 7400-8200
16-18 years 10300-10900 8400-8500
19-30 years 10300* 8400^
31-50 years 9900* 8000^
51-70 years 9100* 7600^
Adults over 70 years 8300* 7200^

Source: National Health and Medical Research Council, .
* estimated energy intake for male 180cm tall, 71.3kg
^ estimated energy intake for female 170cm tall, 63.6kg

The human body is designed for movement and activity, with a need for occasional, regular stops for refuelling and relaxation.
‘ENERGY IN’ comes from the food you consume and is provided by the protein, carbohydrate and fat in the foods that you eat and drink. These nutrients deliver energy in varying amounts. Fat is the most concentrated source of energy, followed by protein and carbohydrate. Alcohol also provides energy but is not really considered a food as it does not provide the body with any extra nutrients – instead, consuming alcohol increases the amount of vitamins and minerals that the body requires.

The amount of energy delivered by the nutrients in food is as follows:

  • Carbohydrates – 16.7 kj per gram
  • Protein – 16.7 kj per gram
  • Fat – 37.7 kj per gram
  • Alcohol – 29.3 kj per gram

Source: National Health and Medical Research Council.
These figures represent the average amount of energy released from these nutrients

‘ENERGY OUT’ refers to the amount of kilojoules burnt up by the body by ‘staying alive’ (which includes factors such as digestion, heart beat, breathing, etc) and by being active. For individuals, the level of energy expended daily depends on age, stage of growth and development, and usual daily activity levels.