We can show that food contains energy by burning some food in oxygen. For example, when a maize cob is burnt, the energy in it is set free as heat and light.
We can measure the energy in food accurately by using a food calorimeter. In this device, a known mass of food is burnt. The heat released warms the water in the calorimeter. From the rise in Temperature of the water, we can calculate the amount of energy in the food sample.
The energy rich nutrients in food are carbohydrates, lipids and proteins. Their energy contents are as follows :
Carbohydrates 1 g contains 16.7 kJ
Fats 1 g contains 37.6 kJ
Proteins 1 g contains 16.7 kJ
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