The word 'energy' is used in a number of different ways...
Energy – it can describe how lively (or tired) a person feels, or refer to the benefits obtained as a result of eating or drinking certain products that may claim to perk you up or boost sports performance.
But when referring to the energy content of food and drink (as seen in a nutrition information panel or front-of-pack %DI labels), the term ‘energy’ refers to the amount of kilojoules found in the product. It is this energy the body uses as a fuel source to function properly.
How is energy measured?
‘Kilojoule’ (kJ) is the measurement unit used when referring to the amount of energy a food or drink contains. The term kilocalories (kcal) (often shortened to calories) is the older imperial measurement that is still used in some parts of the world such as the US and UK. It is also still used by many people in Australia who grew up with this term. One calorie is equal to 4.18 kilojoules, so to convert kilojoules to calories, simply divide the kilojoule figure by 4.18.
The kilojoule content of foods depends on the amount of carbohydrate, fat, protein and alcohol present. Fat contains the highest amount of kilojoules per gram, followed by alcohol, carbohydrate and protein:
- Fat = 37kJ per gram
- Alcohol = 29kJ per gram
- Carbohydrate = 17kJ per gram
- Protein = 16kJ per gram
This means foods that are high in fat are also frequently high in kilojoules, which is why it is often recommended that people reduce their fat intake when they need to reduce their kilojoule intake.1
How do you use energy from food and drinks?
When you eat, the process of digestion converts the energy from foods to another form that the body can use to perform its various functions. Any unused energy is stored, mainly as body fat, for later use. As well as containing kilojoules, foods also contain important vitamins and minerals that help release the energy from food and perform other vital functions in the body.
What are your kilojoule requirements?
The total amount of kilojoules needed by the body each day varies depending on your age, gender, body composition and activity levels. Pregnancy, lactation, growth and illness can all increase your kilojoule requirements. There are Recommended Daily Intakes (RDIs) for kilojoules for people of all ages (click here for the Energy Counter), however as a general guide, an average adult’s kilojoule requirements are 8700kJ per day. The average adult's kilojoule requirement of 8700kJ is what our %DI labels are based on.
Why is it important to know your kilojoule requirements?
All living creatures need energy (kilojoules) from foods and drinks to maintain life. The human body uses energy to maintain basic functions such as breathing, heart function and maintaining body temperature (known as the body’s resting metabolism). Energy is also needed to support voluntary actions such as movement and exercise. Once the body receives enough kilojoules to perform its daily functions, any excess kilojoules (from consuming too much food and drinks, or the wrong types) is stored as fat. It is therefore important to maintain energy balance in the body where the amount of kilojoules taken in is equal to the amount of kilojoules used up. Having excess kilojoule intake over time can cause weight gain, while having too few kilojoules can cause weight loss.
Maintaining a healthy weight
Including a variety of foods such as fruits and vegetables, wholegrain breads and cereals, lean meats or alternatives, dairy products and healthy fats each day is essential to meet the body’s nutrient requirements. Making healthier choices within these key food groups, and including adequate fluid and adequate physical activity every day, can be the difference between weight maintenance or weight gain.
Keeping track of kilojoules in foods
Unless you carry a pocket kilojoule counter book around with you, it can be hard to keep track of your daily kilojoule intake! Food labels in Australia are required to list the kilojoule content of a food or drink in 100grams and also one serve of the food in the product’s nutrition information panel, however most fresh and unpackaged foods do not carry this information. As a general guide, here is the kilojoule content of common foods:2
| Vegetables |
½ cup vegetables or 1 cup salad |
80 kilojoules |
| Fruit |
1 medium piece ( eg apple, orange ) or 2 smaller pieces ( eg apricot ) |
350 kilojoules |
| Breads and cereals |
2 slices of bread, or 2/3 cup of cooked rice or pasta |
600 kilojoules |
| Dairy |
1 glass of skim milk, or ½ a tub of low fat yoghurt, or 40g low fat cheese |
400 kilojoules |
| Meat |
120 grams of raw lean meat or chicken |
600 kilojoules |
| Healthy fats |
3 teaspoons of margarine, 2 teaspoons oil, 2½ tbsp avocado, 10 nuts |
350 kilojoules |
| Drinks |
1 glass ( 250 mL ) of fruit juice, cordial,
Water, diet soft drinks and diet cordials |
450 kilojoules
0 kilojoules |
Kilojoules burnt in activity
The other side of the energy equation is energy expended through exercise. For a general guide on the amount of kilojoules burnt during activity try visiting www.fitness2live.com.au/energy-expenditure
Overall, to maintain energy balance in the body, keep active every day, make healthy food and drink choices and watch your portion sizes!
1 Wahlqvist ML (ed). Australia and New Zealand Food & Nutrition. 2nd edition, 2002.
2 Xyris software, 2004. Foodworks version 3.02
