Calories and kilojoules: What is the difference and what is recommended each day?
Calories and kilojoules (kJs) are actually the same thing – units of energy. Calories and kJs are simply the unit of measure, just like how centimetres and inches both measure length. In Australia, we generally use kilojoules when talking about how much energy is in food.
1 Calorie = 4.2 kJ
1 kJ = 0.24 Calories
If a food has 100 calories, you can times this by 4.2 to get the kJ amount (this equals 420 kJ). If a food has 1200kj, you can times this by 0.24 to get the calorie amount (this equals 288 calories).
When we talk about food containing ‘energy’ it can be easy to get confused by what this means, perhaps thinking that if there is a lot of ‘energy’ in a food that this is a good thing. The energy in food that we put in our bodies is like the petrol that fuels a car. It is important to remember though, that if you consume more energy than you use, weight gain will result.
Calories and kilojoules in food
Food packaging will always state how many kJs are in the food.
Things that influence the amount of kJs in the food you eat include:
- The ingredients in the food
- How it is prepared e.g. frying in oil versus microwaving
- How much you eat (your portion size)
How many kilojoules are recommended per day?
Many packaged and takeaway foods display an average number of kilojoules recommended per day, as 8700 kJ. This number is an average, calculated using a large number of men and women across all age groups. You may need more or less than this.
The amount of kJs you need depends on many things including your age and gender, your weight and your BMI, whether you are trying to lose or gain weight, and how much physical activity you do.
Prepared by Kara Vogt –Accredited Practicing Dietitian