Kilojoules and calories are both a measure of the energy in food which fuels our bodies. Australia now uses kilojoules as the standard measure of energy in foods, but the old system was measured in calories, so its not uncommon to hear people use both terms. The important thing to remember is that they measure the same thing!
4.184 kilojoules = 1 Calorie
How many kilojoules do I need?
There are lots of different factors that go into determining how much energy we need each day – things like your physical activity levels, your age and your gender. As a rough guideline, an average adult needs about 8700kJ per day (2080 Cal).
How many kilojoules do I need to gain/lose weight?
When we eat more energy than our body burns as fuel, the excess is stored as fat. To lose a kilo of fat each week, you need to reduce your energy intake by about 4300kJ (1030 Cal). The maths works just the same in reverse – eating an extra 4300kJ a day will make you gain a kilo each week.