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Encyclopedia > Calorie (food)

Food energy is the amount of energy in food that is available through digestion. Digestion is the process whereby a biological entity processes a substance, in order to chemically convert the substance into nutrients. ...


Food energy is typically measured in units of calories, although the International System of Units unit kilojoule (1000 joules) is becoming more common. In some countries (Australia, for example) the use of kilojoules is de rigueur. Some types of food contain more food energy than others: fats and sugars have particularly high food energy levels. A calorie is a unit of measurement for energy. ... The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ... The joule (symbol: J) is the SI unit of energy, or work. ... Fat is one of the three main classes of food and, at approximately 38 kJ (9 kilocalories) per gram, as compared to sugar with 17 kJ (4 kcal) per gram or ethanol with 29 kJ (7 kcal) per gram, the most concentrated form of metabolic energy available to humans. ... Magnified view of refined sugar crystals. ...


Note that the "calorie" unit used by dieticians for food is equivalent to 1000 times the "calorie" unit used in chemistry (hence it is sometimes called a kilocalorie). One of these "nutritional calories" is approximately equal to 4.1868 kilojoules.


Measuring food energy

In the early twentieth century, the United States Department of Agriculture (USDA) developed a procedure for measuring food energy that remains in use today. The U.S. Department of Agriculture, also called the Agriculture Department, or USDA, is a Cabinet department of the United States Federal Government. ...


The food being measured is completely burned in a calorimeter so that the heat released through combustion can be accurately measured. This amount is used to determine the gross energy value of the particular food. This number is then multiplied by a coefficient which is based on how the human body actually digests the food. A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes. ... A red-hot iron rod cooling after being worked by a blacksmith. ... Combustion or burning is a chemical process, an exothermic reaction between a substance (the fuel) and a gas (the oxidizer), usually O2, to release heat. ... In mathematics, a coefficient is a multiplicative factor of a certain object such as a variable (for example, the coefficients of a polynomial), a basis vector, a basis function and so on. ...


For example, pure sugar releases about 3.95 kilocalories per gram (16.5 kJ/g) of gross energy but the digestibility coefficient of sugar is about 98% in humans, so the food energy of sugar is 0.98 × 3.95 = 3.87 kilocalories per gram (16.2 kJ/g) of sugar.


Energy content

  • Protein contains about 4 nutritional calories per gram (17 kJ/g)
  • Carbohydrates contains about 4 nutritional calories per gram (17 kJ/g)
  • Fat contains about 9 nutritional calories per gram (38 kJ/g)
  • Alcohol contains about 7 nutritional calories per gram (29 kJ/g)

A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Carbohydrates (literally hydrates of carbon) are chemical compounds that act as the primary biological means of storing or consuming energy, other forms being fat and protein. ... Fat is one of the three main classes of food and, at approximately 38 kJ (9 kilocalories) per gram, as compared to sugar with 17 kJ (4 kcal) per gram or ethanol with 29 kJ (7 kcal) per gram, the most concentrated form of metabolic energy available to humans. ... In general usage, alcohol (from Arabic al-kukhul الكحول, al meaning the and kukhul meaning spirit, the chemical) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ...

See also


  Results from FactBites:
 
In Depth - What will be China's food demand in 2025 and 2050? (3173 words)
I have therefore calculated how much China's food commodity demand would increase if the average calorie food intake were to increase to the level of Japan, South Korea, and the USA, and to the average of all developed countries.
The food demand difference between the low and high UN 1998 population projection is in the range of 50 million tons of grain in 2025.
If we compare these food demand scenarios with projections by other authors (see Table 2), we find that estimates from Scenarios A and B are a little lower, but well within the range of their estimates for 2020.
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