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Energy in Foods and Fuels


Our body requires energy for performing various functions. This energy mainly comes from carbohydrates and fats that we take as food. Carbohydrates are decomposed into glucose or its derivatives in the stomach. Glucose is soluble in blood. It is transported by blood cells to various parts of the body where it reacts with oxygen in a series of steps producing CO2, H2O and energy.


C6H12O6(s) + 6O2 (g)  à  6CO2(g) + 6H2O(g)

ΔH = – 2900 KJ

This combustion of glucose, in the human body, takes place at the body temperature because of the catalytic action of enzymes.



Just as the major source of energy in our bodies is the combustion of foods in the similar way, the major source of energy for industries is the combustion of fuels. The efficiency of foods and fuels is compared in terms of their calorific values. The calorific value of food or fuel is defined as the amount of heat produced when one gram of the substance (food and fuel) is completely burnt. The calorific values of some common foods and fuels are given below:

The normal human needs 3000 kcal ( =  14450 kJ) of energy per day. The food consisting of carbohydrates, fats, oils, vitamins, proteins, mineral salts which provide required calories is termed as balanced diet.