Calories are a measure of the energy contained in foods as proteins, fats and carbohydrates. Our bodies use this energy to keep things running, and store any excess as fat for future use.
When we expend energy it is said that we are burning calories, and when we burn more calories than we eat our bodies turn to our fat stores to find the additional energy they require. Thus when we eat more calories than we burn we gain weight, and when we burn more than we eat we lose weight.
Calories and Kilojoules
Depending on what country you live in, you will find nutrition data listed in calories, kilojoules, or both. Our calculators give you the option of calculating in either calories (kcal) or kilojoules (kJ).
A calorie is a unit of measure of the energy required to raise the temperature of 1 gram of water by 1ˇăC. A joule is a unit of electrical energy, commonly used in the physical sciences, equal to the work done when a current of one ampere is passed through a resistance of one ohm for one second. Of course we don't use energy to raise the temperature of water or pass current through resistance, but similar processes maintain our body temperature and perform other bodily functions.
Because calories and joules are so small, when referring to food and energy expenditure it has become common practice to refer to them in multiples of 1,000. The term for 1,000 calories is kilocalories or kcal, and the term for 1,000 joules is kilojoules or kJ.
1 calorie = 4.184 joules
1 kilocalorie (kcal) = 4.184 kilojoules (kJ)
In the scientific and educational communities, it is also common practice to refer to kilocalories as Calories with an uppercase C. However, outside these communities, it has become common practice to simply refer to kilocalories as calories. Therefore when you read 500 calories on a food label it actually means 500 kilocalories, and the same holds true when you calculate an activity that burns 500 calories.
