Usually we heat the food second time to make it hot and eat. As it is our habit to eat most of the food hot.
In some cases we cook the food beforehands and after finishing some work we reheat it again and eat it. Or we reheat leftover foods to eat.
But if you have such habit, be careful now. Studies have shown that reheating some foods can be fatal.
When food is reheated, the nutrients in these foods are destroyed.
There is also a risk of food poisoning when reheated or heated for the second time.