| Revision as of 05:00, 16 November 2005 editR. S. Shaw (talk | contribs)Extended confirmed users, Pending changes reviewers, Rollbackers11,667 edits explain different calories; use common meaning in table← Previous edit | Revision as of 10:56, 23 November 2005 edit undo137.44.1.200 (talk) →Energy contentNext edit → | ||
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| * ''']''' contains about '''4''' nutritional calories per gram (17 kJ/g) | * ''']''' contains about '''4''' nutritional calories per gram (17 kJ/g) | ||
| * ''']''' contains about '''4''' nutritional calories per gram (17 kJ/g) | * ''']''' contains about '''4''' nutritional calories per gram (17 kJ/g) | ||
| * ''']''' contains about '''9''' nutritional calories per gram ( |
* ''']''' contains about '''9''' nutritional calories per gram (38 kJ/g) | ||
| * ''']''' contains about '''7 ''' nutritional calories per gram (29 kJ/g) | * ''']''' contains about '''7 ''' nutritional calories per gram (29 kJ/g) | ||
Revision as of 10:56, 23 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" 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 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 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)
See also
- Chemical energy
- Food chain
- Screaming jelly babies experiment showing food energy.