How to talk to parents?

So, I think I have an ED. I had to do a summer health class (no room in my schedule) and a lot of the signs and symptoms show up in me? I either binge or I fast, excersize like crazy, and have a huge adversion to gaining weight. I don't want to go through this. I know I need help, but my parents don't think EDs/mental illnesses are a real thing. How do I talk to them about this?