I think I now exactly how you feel.
It's strange that I am about in the exact same predicament as you. I've had eating disorder problems for about the last 6-7 months (and body image problems since before that). I am a vegetarian for the animals, but I am not going to lie when I say that being a vegetarian does help keep an ED a secret.
Anyways, about the last 3-4 months I've been going CRAZY on carbs and sweets. Like, seriously. Cereal is also a big thing for me. I eat like 4 bowls in one setting. Thats when I started throwing up. I couldn't handle eating all of that crap and keeping it in me. (For example, today I ate 2 1/2 twinkies already, UGH.)
But, yeah, I know what you mean when you say your parents won't understand. I know tons of people say that their parents don't understand them, but I can honestly say that my mom DOES NOT understand me at all.
I basically flat out told her that I had eating problems. I told her that it would kill me to be over 100 pounds and all that jazz. So, then, you might ask, why am I still here, under 100 pounds, with a full-blown ED? Well, I'm not exactly going to complain, but I don't have an answer for you.
Supposedly, we do not have enough money to put me in one of those 'anorexic houses'. Also, I think my mom is embarrassed of me. If I STRONGLY hint to her that I might need to talk to a counselor or something I'm automatically ungrateful and a spoiled brat. Oh, thats because I have a PERFECT life and I should just be a happy little Barbie doll. Ugh, give me a break.
Haha. Anyways, that was my rant about my mother. Now, I'll give you some advice.
Obviously I couldn't talk to my mom about anything. Or, if I did she just blew it off. So, I did the next best thing; I talked to the school counselor. Well, actually I didn't technically talk to him, I /emailed/ him. I didn't tell him who I was, I didn't tell him anything about me. I just basically told him that I thought I could be in trouble and just need someone to talk to. It has worked wonders these past couple of weeks. I mean, I didn't feel like I was being overwhelmed by everything anymore.
But, yeah, just believe me. It is a TON less uncomfortable when you've talked to him for a while than to just be forced to go in there and explain yourself. And yeah, we've talked, kind of. I haven't really talked to him in person about everything, yet. He's not pushing my though. I'm sure they won't. When I need to talk someone will be there for me. Maybe not my parent's this time. But, at least I'm not alone. (that sounded like a cheesey movie).
Anyways, just do something like that. Be anonymous. Don't make yourself feel trapped just because you don't think you have someone to talk to. Someone will always be there for you.
PS: Sorry for writing a whole novel, there.