Question

how food is known as fuel for our body? explain

Answer 1

our body needs energy to doing work and this energy is obtained from food

Answer 2

Just like the fuel i.e petrol or diesel we put in our vehicles so that they can run or the fuel like woods we use for combustion, similarly the food we eat provides us energy to do our work. Hence it is called the fuel for our body.
Hope that helps you :-)