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The calorie is a unit of energy that originated from the caloric theory of heat. [1] [2] The large calorie, food calorie, dietary calorie, kilocalorie, or kilogram calorie is defined as the amount of heat needed to raise the temperature of one liter of water by one degree Celsius (or one kelvin).
A kilocalorie is the equivalent of 1000 calories or one dietary Calorie, which contains 4184 joules of energy.The notion that "a calorie is a calorie" is related to the idea that weight maintenance is a result of equalizing calorie input and calorie output, [4] and may lead to the practice of calorie restriction.
The calorie is defined as the amount of thermal energy necessary to raise the temperature of one gram of water by 1 Celsius degree, from a temperature of 14.5 °C, at a pressure of 1 atm. For thermochemistry a calorie of 4.184 J is used, but other calories have also been defined, such as the International Steam Table calorie of 4.1868 J.
Kleiber's plot comparing body size to metabolic rate for a variety of species. [1]Kleiber's law, named after Max Kleiber for his biology work in the early 1930s, states, after many observations that, for a vast number of animals, an animal's Basal Metabolic Rate scales to the 3 ⁄ 4 power of the animal's mass.
In general, a gradual calorie deficit of 500 to 750 calories a day is considered safe and sustainable for most people, leading to a weight loss of about one to two pounds a week. Kateryna ...
This data is presented in kilojoules, as most countries today use the SI unit kilojoules as their primary measurement for food energy intake, [4] with the exception of the USA, [5] Canada, [6] and the UK, which use kilocalories or both. [7]
However energy can also be expressed in many other units not part of the SI, such as ergs, calories, British thermal units, kilowatt-hours and kilocalories, which require a conversion factor when expressed in SI units. The SI unit of power, defined as energy per unit of time, is the watt, which is a joule per second. Thus, one joule is one watt ...
A nutritional Calorie is equivalent to a thousand chemical or thermodynamic calories (abbreviated "cal" with a lower case "c") or one kilocalorie (kcal). Because food energy is commonly measured in Calories, the energy density of food is commonly called "caloric density". [ 7 ]