In the song, she talks about everyone being beautiful no matter what size they are. She does not hate on skinny people and even goes so far as to say, 'I know you think you're fat, but I'm here to tell you, every inch of you is perfect from the bottom to the top'. In now way is she telling people to go out and stuff their faces with whatever they can get their hands on. She's saying that you shouldn't let the opinions of the 'famous magazines' that claim only 'size 2' is sexy, get you down. She's telling everyone to happy with who they are and that they CAN be sexy no matter their weight. That those 'famous magazines' don't have to set the standard for us.
In the end, she says if you can't appreciate her for who she is, then you can 'move along'. And she's right. Weight doesn't define who we are, it's our character. Many people could take a lesson or two from this song. And the skinny people who are too stupid to read the words which are clearly printed above, shouldn't even bother. If you don't understand it, then don't bother commenting in the first place.