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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 (thermochemical calorie) is equal to exactly 4.184 J, and therefore one kilocalorie (one large calorie) is 4184 J or 4.184 kJ.
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]
Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. [1] It is reported in energy units per unit time ranging from watt (joule/second) to ml O 2 /min or joule per hour per kg body mass J/(h·kg).
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.
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]
The joule (/ dʒ uː l / JOOL, or / dʒ aʊ l / JOWL; symbol: J) is the unit of energy in the International System of Units (SI). [1] In terms of SI base units, one joule corresponds to one kilogram-square metre per square second (1 J = 1 kg⋅m 2 ⋅s −2).
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.
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.