A calorie is a unit of energy that measures how much energy is in a particular food or drink. It is a way of describing how much energy your body could get from eating or drinking it. The amount of energy in food or drink is measured in calories. The term calorie has been in use since the early 19th century, when it was used to define the amount of heat required to raise the temperature of a kilogram of water from 0 degrees to 1 degree Celsius. There are two main definitions of calorie in wide use: the large calorie or kilogram calorie, which was originally defined as the amount of heat needed to raise the temperature of one kilogram of water by one degree Celsius, and the small calorie or gram calorie, which was defined as the amount of heat needed to cause the same increase in one gram of water. Thus, 1 large calorie is equal to 1000 small calories. In some parts of the world, such as parts of Europe or Australia, people use the term kilojoules instead of calories. One calorie is equal to 4.2 kilojoules.
Calories are important because we need them to give us enough energy to move around, stay warm, grow, work, think, and play. Even our blood circulation and digestion need the energy gained from calories in order to function well. However, eating too many calories and not burning enough of them off through activity can lead to weight gain. As a guide, an average man needs 2,500kcal a day and an average woman needs 2,000kcal a day, but this could be different based on factors such as age, weight, and activity level. To manage calorie intake, one can plan their meals, look for calorie information on restaurant and takeaway menus, and be aware that the more energy spent doing an activity, the more calories will be used.
