Calorie

Calorie (pronounced kal-uh-ree)

(1) In thermodynamics (called also the gram calorie or small calorie), an amount of heat equal to 4.1840 or 4.1868 joules (depending on definitional table used); the standard abbreviation is cal.

(2) In physiology, a unit equal to the kilocalorie, used to express the heat output of an organism and the fuel or energy value of food.

(3) A quantity of food capable of producing such an amount of energy.

1819: From the French calorie, from the Latin calor (genitive caloris) (heat), from the primitive Indo-European kle-os- (a suffixed form of the root kele- (warm)), the construct being calor- + -ie (the noun suffix).  The suffix -ie was a variant spelling of -ee, -ey & -y and was used to form diminutive or affectionate forms of nouns or names.  It came to be used also (sometimes in a derogatory sense) to form colloquial nouns signifying the person associated with the suffixed noun or verb (eg bike: bikie, surf: surfie, hood: hoodie etc).  The now obsolete spelling was calory.  The phrase calorie-counting (or calorie-watching), describing a more “scientific” approach to weight-regulation, dates from 1908.  Calorie is a noun, caloric is a noun & adjective and calorific is an adjective; the noun plural is calories.

Rendered obsolete by experimental progress in the mid-nineteenth century, caloric theory held that the phenomenon of heat could be described as a self-repellent fluid (caloric) that flowed from hotter to colder substances or objects.  In fluid dynamics, caloric was also held to be a weightless gas able to pass in and out of pores in solids and liquids.  It was replaced by the mechanical theory of heat but didn’t completely disappear even from scientific literature until early in the twentieth century.  It’s that history which explains the duality of the meaning of the word “calorie”.  The kilogram calorie (known also as the food calorie, large calorie or dietary calorie) was originally defined as the quantity of heat needed to raise the temperature of 1000 grams (one kilogram) of water by 1^o Celsius (or one kelvin).  The gram calorie (known also as the small calorie) was the quantity of heat raise the temperature of one gram of water by the same 1^o; the relationship between the small & large calorie thus mirrors that of the gram & kilogram: 1:1000.  Both definitions of calorie are from the 1800s: the small in the early years, the large late in the century (recorded by 1866 in French & 1870 in German.

Until relatively recently, in science (mostly physics, chemistry and other fields in which fluid dynamics matter), the gram calorie was used as a unit of measurement (and in the vernacular was “the calorie”, the kilocalorie referenced when necessary) but it was never formally made part of the metric system (SI) and has for almost all purposes been rendered obsolete by the standard SI unit of energy: the joule.  For decades there were inconstancies in the way different bodies expressed the “conversion rate” between calories and joules but in both thermochemistry and nutrition, one small calorie is now held to equal to exactly 4.184 joules, one kilocalorie thus 4184 J (4.184 kJ as expressed by nerds).  Only in the industrial production of food is there still some attachment to the old (4.1840) value, reflected in product packaging although European Union (EU) legislation now insists on the use of “kilocalorie” on labels for consumer products.  In nutrition and food production, the term calorie (usually expressed with the standard abbreviation “cal”) refers almost always to the kilocalorie and is a (more-or-less) standardized expression of the energy value of foods (usually in terms of the (1) the whole packet or quantity in which it’s supplied, (2) a nominal “standard serving” or (3) a standardized metric (eg per 100 grams).  Although sometimes misunderstood, the unit is measure of the energy released by food as it is digested by the human body.

Lindsay Lohan during her early century, peak calorie-counting period.

Although it’s something of a blunt-force measure which doesn’t of necessity correlate with an ideal nutritional intake, the World Health Organization (WHO) and many national and sub-national bodies have issued guidelines for daily calorie intake based on age, sex, activity level, and other factors.  The WHO cautions their recommendations are merely part of the calculations which should be made when constructing healthy diets and calorie counts should be thought a framework for a nutritional model.  The WHO suggests that as a general principle, an average sedentary adult woman requires 1,800-2,200 while the equivalent man will need 2,200-2,700 although these approximations need to be read in conjunction with an assessment of an individual’s metabolism, body composition, and physical activity level.