Should I come out to my parents ?

I am transgendered. To be precise I'm androgynous in mind, but I can't stand my distinctly feminine body and the stigmas that come attached to it. Being reminded I'm a girl makes me cringe, because deep down, I know I'm not. My identity issues aren't the subject here, so I'll cut to the chase. I want to begin dieting and exercising to make my body more masculine, but if I don't explain to my parents why, they certainly will think I'm being excessive. But, I refrain from telling them, because I'm afraid they won't take me seriously. They might dismiss it as just a phase, or, more probably, as a joke. You see, I don't dress in a masculine way, to fit in. I'm kind of ashamed of being such a coward. Should I take steps to look more masculine on my own first, or should I come out anyway ? (Tolerance and transphobia are not issues. My parents are quite openminded.)