Calorie

A calorie is a unit of measurement for energy. In most fields, it has been replaced by the joule, the SIunit of energy. However, it remains in common use for the amount of energy obtained from food. Many different definitions for the calorie have emerged during the 19th and 20th century. They fall into two classes:

• The small calorie or gram calorie is the energy needed to increase the temperature of 1 gof water by 1 °C. This unit of energy is equivalent to about 4.185 J.

• The large calorie or kilogram calorie is the energy needed to increase the temperature of 1 kgof water by 1 °C. This unit of energy is 1000-times larger than the gram calorie and equivalent to about 4.185 kJ.

The kilogram calorie is today also called kilocalorie (symbol: kcal). The international standard definition of the term "calorie" (symbol: cal) refers today to the gram calorie; this way, the term kilocalorie can also be interpreted to mean 1000 calories. However, where the term "calorie" is used in nutritionand food labeling, it commonly refers to the kilocalorie.

Nutrition and food labels

Image:Nutrition-label.jpg

The "calorie" has become a common household term, because dietitiansrecommend in cases of obesityto reduce body weight by increasing exercise (energy expenditure) and reducing energy intake. Many governments require food manufacturers to label the energy content of their products, to help consumers control their energy intake. In Europe, manufacturers of prepackaged food must label the nutritional energy of their products in both kilocalories ("kcal") and kilojoules ("kJ"). In the United States, the equivalent mandatory labels display only "calories" (meaning kilocalories); an additional kilojoules figure is optional. The energy content of food is usually given on labels for 100 g and for a typical service size.

The amount of food energyin a particular food could be measured by completely burning the dried food in a bomb calorimeter, a method known as direct calorimetry[1]. However, the values given on food labels are not determined this way, because it overestimates the amount of energy that the human digestive system can extract, by also burning dietary fibre. Instead, standardized chemical tests and an analysis of the recipe are used to estimate the product's digestable constitutents (protein, carbohydrate, fat, etc.). These results are then converted into an equivalent energy value based on a standardized table of energy densities:

Other substances found in food (water, non-digestable fibre, minerals, vitamins) do not contribute to this calculated energy density.

Recommended daily energy intake values for young adults are: 2500 kcal/d(10 MJ/d, 120 W) for men and 2000 kcal/d (8 MJ/d, 100 W) for women. Children, sedentary and older people require less energy, physically active people more.

Versions

Three definitions of the calorie are today recognized internationally:

Other historic definitions include

• the 4 °C calorie, and
• the mean 0 °C to 100 °C calorie.

Of all these, what is most commonly meant by calorie in contemporary English text is the 15 °C calorie. Since these many definitions are a source of confusion and error, all calories are now deprecated, especially for precise measurements. The International System of Units (SI)unit for heat (and for all other forms of energy) is the joule(J).

In nutrition, the difference between these calorie definitions is of no practical relevance, because nutritional calories are not measured amounts of energy, but are calculated from food composition. This calculation uses internationally agreed conventional conversion factors, which are generously rounded values that roughly approximate the average energy density of a large number of different food samples. The exact composition of agricultural products varies far more than the less than 0.1% difference between the above definitions of the calorie as a physical energy measure.

Trivia

• Unicodehas a symbol for "cal": (㎈), but this is just a legacy code to accommodate old code pagesin certain Asian languages, and it is not recommended for use in any language today.

• The conventional value chosen to define a ton of TNT is equal to 1 billionthermochemical calories: 1 t_TNT ? 1 × 10⁹ cal_th. The actual energy liberated from the explosion is somewhat more; see megaton.

• Human fat tissue contains about 87% lipids, which store about 9 kcal/g energy. Therefore, to lose 1 kg of body-fat tissue, the energy of about 870 g pure fat has to be used up, which corresponds to about 7800 kcal (32 MJ), that is one has to create a ?7800 kcal deficit between energy intake and use. (In U.S. customary units, that is about 3500 kcal per pound.)

See also

• Food energy
• Empty calorie
• ISO 31-4

External links

• USDA National Nutrient Database for Standard Reference - Release 18Official publically available reference database and online search. Includes 7,146 foods and is free to download and use. This database is the one used by most websites that provide calorie information.
• CalorieFreak- Searchable and browseable nutrition database
• Calorie CounterSearchable calorie database of over 11,000 foods - Including fast food (website has pop-up ads)
• NutritionData's Nutrition Facts Calorie Counter
• Calorie Counter Database
• Calorie counter and calories burned databaseSearchable database of over 7,000 foods and calories burned for over 600 different activities.

References

• European Union regulations on nutrition labeling
• United Kingdom Food Labelling Regulations 1996– Schedule 7: Nutrition labelling
• United States federal food-labeling regulations 21CFR101.9
• NISTSpecial Publication 811, Appendix B8: calorie.
• Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.ca:Caloria

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This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Calorie Wikipedia article Calorie.