The 'Hairspray' actress talks about her former body image issues.

BRITTANY SNOW is one of 14 celebs, along with ASHLEE SIMPSON and FERGIE, who have signed the Seventeen Body Peace Project Treaty that asks girls to pledge to stop obsessing about the shape of their bodies.

In the issue of Seventeen magazine, now on newsstands, Editor in Chief ANN SHOKET has launched the year-long project to help girls turn off the negative voice in their heads, get some perspective on skinny celebrities, and be more accepting of their own bodies.

So many girls feel awful about themselves," Shoket tells ET in an exclusive interview, "and this [treaty] is a goal that says, 'Just make peace with your body.' Vow to treat it better. Stop obsessing about what it looks like and appreciate it for what it can do."

Brittany, who tells ET she suffered from anorexia, exercise bulimia and suppression, says she always was conscious of her body, especially since she started acting at age four. But it didn't become a serious illness for her until she was 16 or 17 years old.

"I got help when I was 17," she admits. "It was a process and still is a process, but I am 21 years old now, and I have done a lot of hard work. It is a daily thing, but I am 100 percent better than where I was in just little things, like not hating myself in the morning and wearing jeans, and even if they are tight, being okay with myself."

Seventeen is hoping to get one million girls to sign the treaty, but Brittany says speaking out on the issue is important, even if she only gets one girl to get help.

"My main thing that I want to say to girls is that you are not alone in this," relates the 'Hairspray' star, who had two friends who died of an eating disorder. "You are not crazy. The things that you are thinking, and the way that you feel, are not out of the ordinary. So many people are going through this. Celebrities included. There is a way to get help and feel better."