Caloric values of food

Caloric values of foods (physiological fuel values) are enthalpies of combustion but with an opposite sign, (-AH ), and corrected for energy lost in urine (e.g., as urea) and feces. While enthalpies of combustion of foods are all negative, the caloric values are given as positive numbers. Caloric values for proteins are... 

Any serious effort to lose weight usually leads to a study of the caloric values of foods. Where do the numbers quoted on food labels come from ... 

Fats and carbohydrates are the principal sources of energy in foods. Pure fat has a caloric value (heat of combustion) of 4080 kcal per pound, and pure carbohydrate (sugar) a caloric value of about 1860 kcal per pound. The caloric values of foods are obtained by use of a bomb calorimeter, just as was described above for fuels. The third main constituent of food, protein, is needed primarily for growth and for the repair of tissues. About 50 g of protein is the daily requirement for an adult of average size. Usually about twice this amount of protein is ingested. Tliis amount, 100 g, has a caloric value of only about 400 kcal, the heat of combustion of protein being about 2000 kcal per pound. Accordingly fat and carbohydrate must provide about 2600 kcal of the 3000 kcal required daily. 

Table 6-2 of Some Physical Constants Caloric Values of Food Components... 

Adiabatic bomb calorimeters or isoperibolic calorimeters are used to determine the heat of combustion of foodstuffs. Although the values may be important in the context of process safety, they are mainly used to calculate caloric values of food for human nutrition or when foods (usually oils) are used as energy sources for engines. 

By 1900 the caloric value of foods had been carefully determined. Between 1890 and 1900 efforts were made to study food requirements by statistical methods. Dietary studies were conducted in several parts of the world, diets being evaluated for energy and protein according to standards developed by Voit and Atwater. Data collected by Atwater in the United States represent, as stated by McCollum, an epoch in development of knowledge of human nutrition. ... 

Also see BOMB CALORIMETER CALORIC VALUES OF FOODS CALORIE [Energy] EXPENDITURE and METABOLISM.)... 

The phenomenon of interchangeability was discovered by physiologists more than 50 years ago and has been the basis of calculations of the caloric value of food intake. Problems of nutrition connected with these interrelationships will be discussed in Chapt. XXI. 

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