Fuel Values of Foods and Other Substances

The important difference between metabolism and combustion is that the latter is usually a one-step, high-temperature process. Consequently, much of the energy released by combustion is lost to the surroundings. 

Various foods have different compositions and hence different energy contents. The energy content of food is generally measured in calories. The calorie (cal) is a non-SI unit of energy that is defined as the amount of energy required to heat 1 g of liquid water by 1°C and is equivalent to 4.184 J. In the context of nutrition, however, the calorie we speak of (sometimes called a nutritional calorie or big calorie ) is actually equal to a kilocalorie, that is, 

Note the use of a capital C to represent the big calorie. The bomb calorimeter described in Section 7.3 is ideally suited for measuring the energy content, or fuel value, of foods. Fuel values are just the enthalpies of combustion (see the table). In order to be analyzed in a bomb calorimeter, food must be dried first because most foods contain a considerable amount of water. Because the composition of particular foods is often not known, fuel values are expressed in terms of kJ g rather than kJ mol .  

Fuel Values of Foods and Some Common Fuels 

Serving Size 6 cookies (28g) Servings Per Container about 11 

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