Calorie Definition and Weight Loss

The food calorie is sometimes capitalized as Calorie to distinguish it from the chemistry calorie; however, this capitalization is rarely observed in practice.

The Nutrition Calorie

Nutritionists measure the energy content of food in "calories" (sometimes capitalized and abbreviated as Cal or sometimes C, or abbreviated kcal as if small calories were being used), where each food calorie represents 4,186 joules. This is equivalent to 1000 of the calories used in chemistry, and thus the food Calorie would be called a kilocalorie if small calories were being used. However, in chemistry calories have been deprecated as a scientific unit of measure in favor of joules, and therefore in common modern usage the word "calorie" usually refers to a food calorie.

This situation provides two ways of talking about the amount of calories in food which look quite different but that express the exact same amount of energy. One may say that dietary fat has nine kilocalories (kcal) per gram, while proteins and carbohydrates have four kcal per gram, or, one may say that fat has nine Calories per gram while carbohydrates and proteins have four Calories per gram.

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. Dieticians recommend counting calories to avoid obesity. The government of the United Kingdom recommends consumption of no more than 2000 Calories (2000 kcal) by women each day and 2500 Calories (2500 kcal) by men each day.

The Physics and chemistry calorie

In physics or chemistry, a calorie (abbreviated cal) is a unit of energy that equals the amount of heat necessary to raise the temperature of one gram of water by 1 degree Celsius, at a pressure of 1 atm. This amount of heat depends somewhat on the initial temperature of the water, which results in various different units sharing the name of "calorie" but having slightly different energy values:

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