Kilojoules are a more modern way of measuring energy (in the same way that kilometres are a more modern way of measuring distance). Kilojoules are shortened to kJ on food labels. One kilocalorie equals 4.2 kilojoules so the amount of kilojoules in a food will always be a much bigger number. New labelling laws means kilojoules, as well as kilocalories, are now often shown on the front of food labels.
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