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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).
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.
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 energy provided by macronutrients in food is measured in kilocalories, usually called Calories, where 1 Calorie is the amount of energy required to raise 1 kilogram of water by 1 degree Celsius. [27] Carbohydrates are molecules that store significant amounts of energy. Animals digest and metabolize carbohydrates to obtain this energy.
Food energy is chemical energy that animals (including humans) derive from their food to sustain their metabolism, including their muscular activity. [ 1 ] Most animals derive most of their energy from aerobic respiration , namely combining the carbohydrates , fats , and proteins with oxygen from air or dissolved in water . [ 2 ]
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]
Obese individuals burn more energy than lean individuals due to increase in the amount of calories needed to maintain adipose tissue and other organs that grow in size in response to obesity. [2] At rest, the largest fractions of energy are burned by the skeletal muscles, brain, and liver; around 20 percent each. [2]
≈ 1 food Calorie (large calorie) ~7×10 3 J: Muzzle energy of an elephant gun, e.g. firing a .458 Winchester Magnum [100] 8.5×10 3 J Kinetic energy of a regulation baseball thrown at the speed of sound (343 m/s = 767 mph = 1,235 km/h. Air, 20°C). [101] 9×10 3 J: Energy in an alkaline AA battery [102] 10 4 1.7×10 4 J