A calorie is a unit of energy that originated from the obsolete caloric theory of heat. There are two main definitions of "calorie" in wide use. The large calorie, also known as food calorie, dietary calorie, or kilogram calorie, was originally defined as the amount of heat needed to raise the temperature of one kilogram of water by one degree Celsius. The small calorie, or gram calorie, was defined as the amount of heat needed to cause the same increase in one gram of water. In nutrition and food science, the term calorie and the symbol cal may refer to the large unit or to the small unit in different regions of the world. It is generally used in publications and package labels to express the energy value of foods in per serving or per weight, recommended dietary caloric intake, metabolic rates, etc. The precise equivalence between calories and joules has varied over the years, but in thermochemistry and nutrition, it is now generally assumed that one small calorie is equal to exactly 4.184 J, and therefore one kilocalorie (one large calorie) is 4184 J, or 4.184 kJ.
In practical terms, calories are important for providing the energy needed for the body to function properly. The amount of energy in food or drink is measured in calories, and the body uses this energy to function properly. To maintain weight, the calories used by the body should be the same as the amount of calories consumed. If more calories are consumed than used, the body stores the extra energy as fat, leading to weight gain. Conversely, if fewer calories are consumed than used, the body uses its stored fat for energy, resulting in weight loss. Calorie information is often given in kcals, which is short for kilocalories, and can vary based on factors such as age and weight. For example, an average man needs 2,500kcal a day, while an average woman needs 2,000kcal a day.
In summary, a calorie is a unit of energy that is essential for human health. It is important to be mindful of calorie intake and expenditure to maintain a healthy weight and overall well-being.
