What are Calories and Kilojoules?
Calories and kilojoules are both units of energy contained in food. They measure the same thing and the only difference is the system used. Calories are the official system of the USA. In Australia, New Zealand, and other parts of the world, we use the metric system of kilojoules.
How to Convert Calories to Kilojoules?
1 calorie = 4.184 joules.
If you know how many calories are in a food you multiply by 4.184 to get kilojoules.
If you know how many kilojoules are in a food you divide by 4.184 to get calories.
So where do food kilojoules come from?
The main food components or macronutrients all provide a different number of kilojoules per gram:
- Fat – 37 kilojoules (9kcal) per gram
- Carbohydrate – 17 kilojoules (4kcal) per gram
- Protein – 17 kilojoules (4kcal) per gram
- Alcohol – 29 kilojoules (7kcal) per gram
The ratio of macronutrients in a food or meal is what gives the total kilojoule value.
What does this mean for weight loss?
If you’re trying to lower your kilojoule intake, what is important is the amount of kilojoules in a portion of food or the “energy density”. Foods with a high energy density have lots of kilojoules in a small serving and are typically low in water content. Foods with a low energy density have fewer kilojoules for the same weight or portion and are good choices for weight loss.
Take grapes and sultanas as an example. For the same amount of kilojoules you can eat roughly ¼ cup of high energy density sultanas or close to two cups of lower energy density grapes! Which would leave you feeling more satisfied?
If you add more fat to a recipe, you’ll raise the energy density or kilojoules per portion even with healthy types. So still enjoy your goat’s cheese salad but practice a little portion control when you crumble it on.
And if you add water (like in the grapes example), you’ll in effect dilute the kilojoules and lower the energy density (think soups, smoothies, tajines). Fibre in wholegrains, legumes, fruit and vegies are also great additions, as they add bulk to bust hunger and lower the energy density without providing kilojoules.
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