The main problem with microwave ovens is that although it has a metal grid at the door to prevent the output of microwave radiation to the outside, in reality a person in front of a microwave oven is receiving a radiation of several V/m (Electric field strength),.and these radiations are harmful to health  http://www.bioinitiative.org/

That without going into evaluating the effects that microwaves can have on the food we consume, subject of which there is a wide debate.

For that reason it is not advisable to cook food (which means that it has been working for a long time and therefore radiating), but simply using the microwave oven to heat the food.

Regards

Dear Dr. Piyush Malaviya,

Please have a look at these useful links.

Thesis Effects of Electromagnetic Radiation from Microwave Ovens on...

Article Adverse Effects of Microwaves

Article Health Effects of Microwave Radiation -Microwave Ovens Healt...

http://www.vsan.org/rok-az/misc/HazardsOfMicrowaveCooking.pdf

Good luck!