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In scientific contexts, the name "calorie" refers strictly to the gram calorie, and the unit has the symbol cal. SI Prefix es are used with this name and symbol, so the kilogram calorie is known as the "kilocalorie" and has the symbol '''kcal'''. Colloquially, and in Nutrition and food labelling, the term "calorie" almost always refers to the kilogram calorie. This applies only to English text; if an energy measurement is given using a unit symbol then the scientific practice prevails there. A convention of capitalising "Calorie" to refer to the kilogram calorie, with uncapitalised "calorie" referring to the gram calorie, is sometimes proposed, but neither recognized in any official standards, nor commonly followed. The conversion factor between calories and joules is numerically equivalent to the Specific Heat Capacity of liquid water (in SI Unit s). NUTRITION AND FOOD LABELS .]] The "calorie" has become a common household term, because Dietitian s recommend in cases of Obesity to 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 serving size. The amount of . 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 The energy needed to increase the temperature of 1 G of water by 1 °C varies depending on the starting temperature, and is in any case difficult to measure precisely. Accordingly there have been several definitions of the calorie:
The two perhaps most popular definitions used in older literature are the "15 °C calorie" and the "thermochemical calorie". Since the many different definitions are a source of confusion and error, all calories are now (J). In nutrition, the difference between these calorie definitions is of no practical relevance. This is, because nutritional calories are not measured amounts of energy, but are calculated from food composition. Such calculations use 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
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