As many others here will no doubt tell you, and as disappointing it will be to read, I'm afraid magic doesn't work like that. Magic can't change your height, weight, eye color, sex, DNA, etc. At least not on the physical plain. Magic can indeed help change certain things, but it's on a subtle level and not an instantaneous process. What you desire to happen also has to be physically possible. Magic works within the laws of physics; it doesn't violate them.
I will like to add magic can defiantly help you lose weight or gain muscle. But it only can go so far sadly. It can make the destination but you still have to ride the bus. Meaning you will still have to eat better and exercise. I know the question was different from my response, but I just wanted to add my two cents.