Talk to your Dad and tell him how you feel. It doesn't have to be a 5-hour conversation but make sure to get it all out. I wouldn't expect him to stop and change right away. It'll take some time but it will definitely be worth it. Your Dad seems to love you and I'm sure that he will understand - despite his own perception of women and their size. It's a really bad coincidence that his wife - who he's around most of the time - is so tiny. She seems to have no problem keeping up what she's been doing to look like that which is probably why he makes mean comments towards you thinking in his head "it's really not that hard", if so-and-so can do it, so can my daughter! So, on top of being worried about you, your health and looks, he's got that in his head as well.
Just don't forget - you're awesome!