Body image is something many of us struggle with. Some of us think we're too fat. Others think they're too thin. Some take these images to an extreme, which is where we get eating disorders. These are illnesses that need to be treated as such. As far as I know, those of us who have fought them don't ever truly recover. There's a chance that we could relapse. Our body image issues can be brought back by as simple a thing as a comment that feeds into our insecurities.
If you have body image issues, if you aren't happy with how you look, change it. Talk to your doctor. See what he/she/ze says. If you don't agree with them, say so. Don't be afraid. The only thing stopping you from getting help is yourself. Sometimes they'll do something you don't appreciate. Other times their advice will help you.
Eating disorders are nothing to consider as a passing phase. They can lead to a person's death. You need help. If you know someone who has one, talk to them. Encourage them. Try to give them as much support as you can. If you can, talk them into getting help. Tell them to talk to their doctors. Don't tear them down about their appearance. Don't tell them you wish you were as thin as they were. Don't tell them they're fat and need to lose weight. Just support them as they come to a place where they can resolve their issues.