If it causes lots of metabolism, one plausible side-effect might be increased cancer risk. But you have to balance that against all the risks of obesity.
Or you could, you know, eat less in quantity, better in quality? Have a look at what your ancestors from a few generations back - not so far that they were chasing deer with clubs, far enough that they weren't eating so much heavily processed stuff - were eating and take a clue from that. This also has side effects but you'll end up liking them instead of having to go to the doctor for yet another prescription to combat them (which has side effects, which causes you to... rinse and repeat).