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Science: The amount of heat required to raise the temperature of a unit of water, at or near the temperature of maximum density, one degree Celsius (or Centigrade [C]); expressed as a "small calorie" (the amount of heat required to raise the temperature of 1 gram of water one degree C), or as a "large calorie" or "kilogram calorie" (the amount of heat required to raise one kilogram [1,000 grams] of water one degree C); capitalization of the word calorie indicates a kilogram-calorie. (Source: U.S. Department of Energy)
Food: Nutritionists measure the energy content of food today in both "calories" (large calories) or "kilojoules" (kJ), a usage widely known in the general population and (confusingly) often referred to as a "kilocalorie" as though small calories were being used. Sporadic attempts have been made, particularly in the United States, to write the kilogram calorie capitalized as Calorie and abbreviated as Cal, to alleviate the confusion with the chemical definition of the term "calorie" as a small calorie. This alternate notation has no legal standing, and is not endorsed by any standards body.
The amount of food energy in a particular food is measured by completely burning the food in a bomb calorimeter, a method known as direct calorimetry. For example, dietary fat has about 9 kcal/g, while proteins and carbohydrates have about 4 kcal/g. Recommended daily energy intake values for average adults are 2500 kcal/d (10 MJ/d) for men and 2000 kcal/d (8 MJ/d) for women.
The "calorie" has become a common household term, because dietitians recommend in cases of obesity to reduce body weight by increasing exercise (energy expenditure) and reducing energy intake. (Source: Wikipedia.org)
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