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The food being measured is completely burned in a ] so that the ] released through ] 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 ] which is based on how the human body actually digests the food. The food being measured is completely burned in a ] so that the ] released through ] 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 ] which is based on how the human body actually digests the food.


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 .98 * 3.95 = 3.87 kilocalories per gram (16.2 kJ/g) of sugar. 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 .98 × 3.95 = 3.87 kilocalories per gram (16.2 kJ/g) of sugar.


== Energy content == == Energy content ==

Revision as of 04:06, 16 November 2005

Food energy is the amount of energy in food that is available through digestion.

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 has come to dominate. Some types of food contain more food energy than others: fats and sugars have particularly high food energy levels.

Note that the "calorie" used by some dieticians for food is actually a kilocalorie; it 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 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.

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 .98 × 3.95 = 3.87 kilocalories per gram (16.2 kJ/g) of sugar.

Energy content

  • Protein contains about 4 (nutritional) kilocalories per gram (17 kJ/g)
  • Carbohydrates contains about 4 kilocalories per gram (17 kJ/g)
  • Fat contains about 9 kilocalories per gram (32 kJ/g)
  • Alcohol contains about 7 kilocalories per gram (29 kJ/g)

See also

Category: