Energy values, of foods

Energy values of food can be estimated on the basis of the content of carbohydrate, protein, and fat ... 

The energy value of food is indicated in calorie unit. 

The unit used in discussing the energy value of food is the Calorie (Cal), equal to 1000 calories or 1 Idlocalorie (kcal). In the SI system, the unit of energy is the joule (J), and 1 calorie = 4.1868 J. 

Many years ago, chemists measured heat in calories instead of joules. A calorie is the heat required to raise the temperature of 1 g of liquid water by 1°C. A kilocalorie is a unit equal to 1000 calories. One calorie is equal to 4.184 J. One joule is equal to 0.239 calorie. Some nutritionists and dietitians still use Calories but are switching to kilojoules. The energy value of foods is measured in units called Calories. Note the capital C. 

Measuring Energy Changes Calorimetry Energy Value of Food Energy Economics MiniLab 20.2 Heat In, Heat Out CbemLab Energy Content of Some Common Foods 719... 

The SI unit of heat is the joule (J) (Table 1.4). The kilojoule (1 kJ = 1000 J) is a convenient unit to use to express energy values in laboratory studies. The metric unit of energy is the calorie (cal), equal to 4.184 J. Throughout the liquid range of water, essentially 1 calorie of heat energy is required to raise the temperature of 1 g of water by 1 °C. The calories that most people hear about are those used to express energy values of foods and are actually kilocalories (1 kcal = 4.184 kJ). 

As a consequence of their differing digestive systems and related metabolism, different systems are used for expressing the energy value of foods according to the type of animal concerned. Chapter 12 describes these systems and the methods used to predict the energy value of foods. 

Factors affecting the metabolisable energy values of foods... 

As stated above, until recently, the energy system used for pigs in the UK was based on DE. However, after extensive consultation with the industry and other stakeholders, an NE system was introduced in 2003 (see Further reading). In this system, both energy requirements and the energy value of foods are expressed in terms of NE. As explained previously (see Chapter 10), the NE value of a food is... 

The introduction of new methods of analysis, such as near-infrared spectrometry (NIRS), has speeded up the prediction of digestibility and energy values for a range of foods (see Chapter 10). However, it must be remembered that all laboratory methods of predicting the energy value of foods are dependent on the availability of reliable data obtained from properly conducted metabolism trials with animals. It is the systematic evaluation of many food samples in such trials that provides the regression equations that are subsequently used to predict energy values from laboratory measurements. 

The energy value of some foods is variable. Consequently, most systems include equations for predicting the energy value of foods from their chemical composition determined by laboratory analysis. 

The energy requirements of ruminant animals and the energy values of foods are currently expressed in the UK in terms of metabolisable energy (see Chapters 11 and 12). 

Livesey, G (1984) The energy equivalents of ATP and the energy values of food proteins and fats. Br. J. Nutr., 51, 15-28. 

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