Like many women, I've always been self-conscious about my weight. (This is going somewhere writing related, I promise: bear with me.) Even at my thinnest, I knew I would never be down to slender - there's a point at which bone structure intervenes, and I have healthy doses of Italian and German in my genetic background.
So when I started writing, if I ever considered my characters' weight and bone structure, they tended to be slender, thin ... and in a few cases, even borderline unhealthy. I was even uncomfortable writing a heavier character. I was pretty rocked when I read Pigs Don't Fly, and the main character Summer suddenly breaks down about her sizable weight. Wait (no pun intended), what?
Fairly obvious this was wish fulfillment for me, but how many wishes does one need? I started working on recognizing this tendency and varying it ... when it comes up in the story. My RPG characters tend to still follow this mode, because gaming - especially MU* gaming, which is more immersive - is more of a lark, more an opportunity to "be" exactly who you want, rather than telling a specific story.
I had a similar pattern with the height of my characters. When I was little, I was told that I would probably end up around 5'11". Having maxed out at 5'6.5", I was for a long time irrationally furious at the world. Oh, the angst! It's no coincidence that (again, particularly in RPGs) my ladies tended to be very tall ... or, because I was intrigued by the logistics of it, very short.
Recognizing the pattern is the first step to changing it, of course, but I still indulge in it now and again. It's a bit like having a bowl of fictitious ice cream. And isn't all fiction wish fulfillment, in the end, even if it's for something shallow and superficial?