I've noticed that she tends to joke about getting fat a lot, like in this video where she's talking about making the "California Gurls" music video and says "I'm obsessed with all things edible. First it was fruit, and now it's cotton candy and cakes. And I'm gonna be fat probably by my fourth record."
Then of course there was this tweet where she posted a weight gain morph of herself:
I know it probably doesn't mean anything, but if she WAS a closet feedee she'd probably make the same jokes knowing that most people would just laugh and not catch on.