People who find pleasure in doing so many other things eat to live, but there are a few others who live to eat. Not because they might not have anything else interesting to do in life, but it is because of their love for food. Junk food can always build up fat in your body. This is completely unnecessary for the body, and when it crosses a limit, it becomes a liablity, your heart would need to pump blood to the useless fat in your body as well, and your legs would need to support its weight while walking.
It is not advisable to let fat collect in your body, and it is advisable to burn it away as soon as possible.
There are so many artificial and synthetic fat burners out there that can be chosen, but you never know if its burning only the fat and what all side effects it might have. So, the best thing to go for would be natural fat burners.