8 XXX : NakedProgress

It's just fat. You lose it the same way you lose any fat, by having a caloric deficit. As everyone keeps saying, you can't spot reduce or choose where you lose fat (or where you store it when you gain it). They always say, "first on, last off" for that sot of thing. I'm not sure if there's any science to that but, anecdotally, it seems pretty sound. Cut calories and you'll lose it eventually.
You just have to burn more calories! You can't spot-treat a single area so just keep going until you get there and maintain it. You can do it! (: My core is one of my weaker parts, what are some of your routines for it?