Britney Spears SM50cover_230.jpg Britney's back on stage, looking trim and toned, so it must be those gym sessions and dance rehearsals right?

Well, Star reports that Brit's ab-solutely fabulous figure is the result of her starving herself, "abusing a prescription drug," and twice weekly colonics. Yikes!

A source for the magazine reveals that Brit was "having trouble losing the last five to 10 pounds," so she started going to extreme measures to stay slim. The source adds that sometimes the pop princess will go for days without eating any solid food.