It's the brain, silly. Silly brain!
Fluctuations of Body Images in Anorexia Nervosa
It was not until I'd lived in eating disorder world for a while that I realized that my own body image fluctuates. I see someone different in the mirror and carry around a different body day to day. It is generally a lunar cycle, actually - and not surprisingly as part of it must be hormonally influenced - I also note that stress, screwing up, the meanness of others, and bad news cycles play havoc as well . Pre-ED world, I would do like most women and look at myself sideways and say "hey, girlfriend, looking good today!" and spend the day sashaying happily through my day. Or, on those bad days, I'd see this lumpy, ugly, frumpy person and resolve to go buy a product or do more time on the exercise bike or skip dessert in an attempt to correct the miscreant mirror. The greatest thing about learning about body dysmorphia and body image schema was to realize that while I saw these changes I was really the same person throughout and that others saw that same person - I wasn't going to change her, and she was - gosh darn it - "good enough." I have the self-esteem, most of the time, to believe others see the Laura I prefer and give a mental snub to those blind to her charms. It's saved me buckets of money on beauty products!
P.S. I dare you to say that Miss Piggie is the one with body image problems!