Fat Boys' Prince Markie Dee Plans Not So Fat Comeback

43-year-old Prince says he's lost 175 pounds in the last six years ... down from 450 -- telling us, "I am not young anymore. I cant go eat a couple of Big Macs a day and not worry about it. I have to watch what I eat and care about my diet. I have kids to live for."

Prince -- real name Mark Morales -- says he's also planning a huge comeback after a 12-year hiatus ... and has even signed with a label called Uncle Louie Music Group to put out an album.