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03 December 2008

Calories, kilojoules: which is it?

If you're confused about the difference between calories and kilojoules, or the amount of food you need to cut out of your diet to lose weight, this article is for you.

If you're confused about the difference between calories and kilojoules, the amount of food you need to cut out of your diet to lose weight and the whole concept of "negative-energy foods", this article is for you.

Calories = kilocalories
Strictly speaking, the non-metric unit of energy is the kilocalorie or kcal, which equals 1000 calories. South Africans are used to the idea of kilojoules (kJ) and use the term when we speak of the amount of energy in foods or when describing how much energy we've used during exercise.

The scientific definitions are:
  • Calorie: The amount of energy required to raise the temperature of 1 millilitre of water by 1 degree Celsius at 15 degrees Celsius.
  • Kilocalorie: The amount of energy required to raise the temperature of 1000 millilitres (or 1 litre) of water by 1 degree Celsius at 15 degrees Celsius.

Kcal vs kJ
Both a kilocalorie and a kilojoule are a measure or unit of energy. If you say that a food contains 100 kcal or 420 kilojoules, this means that if the food is completely metabolised, 100 non-metric units or 420 metric units of energy will be released for use by the body. Apart from needing energy for physical activity, the body uses energy to keep the basic metabolic processes (digestion, breathing and so forth) running.

How many kcal/kJ must I eat if I want to lose weight?
Generally speaking, we need to reduce our energy intake by 500 kcal or 2100 kJ a day to lose between 0.5 and 1kg a week – a rate that will help to keep the weight you lose from being regained.

Is food X fattening?
Most foods and drinks are potentially fattening if consumed in excess. This means that even if you only eat healthy foods (yoghurt, fruit, vegetables, vegetarian etc), you'll still put on weight if you take in more energy than you need. The fact that a food or beverage has excellent nutritional properties doesn't mean that it doesn't have the potential to make you fat.

Any questions? Ask DietDoc

 
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