ENERGY
VALUE OF FOODS
The energy in various foods is
measured by calorimetry. Calorimetry is the measurement of heat loss.
An instrument for measuring heat output of the body or the
energy value of foods is called a Calorimeter. In measuring the calorie value
of foods, Bomb calorimeter is used. The maximum amount of energy that the
sample is capable of yielding when it is completely burnt or oxidized is the
energy value of that food, also known as heat of combustion.
The energy measured using a Bomb Calorimeter is as follows
1g
of Carbohydrate - 4.1 kcal
1g
of fat - 9.45 kcal
1g
of protein - 5.65 kcal
When samples of Carbohydrate, Fat, Protein are burned, the
amount of heat produced is always the same for each of these nutrients.
In the bomb calorimeter
carbohydrates, fats and proteins are completely oxidized whereas in the human
body the process of digestion and absorption does not proceed with 100 percent
efficiency. The extent of digestion varies from one nutrient to another.
The Coefficient of digestibility is
used to express the proportion of an ingested nutrient that ultimately becomes
available to the body cells.
The coefficient of digestibility for carbohydrate, fat and
protein are 0.98, 0.95 and 0.92 respectively. It is observed that carbohydrate
and fat are metabolized almost completely, Whereas protein metabolism is
incomplete due to the presence of nitrogen. The physiological energy value of
carbohydrate, fat and protein are 4, 9 and 4.
These
values are known as Atwater Bryant factors or physiological fuel values as
given in table-20A.
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