How do you bring up an eating disorder to a friend?!

How do you bring up an eating disorder to a friend?

i did a research paper over anorexia nervosa and i learned a lot about it. and now when i think of all the things i learned.. im afraid that one of my friends might be anorexia. but i dont know how to bring it up with my other best friend. i dont even know if i should, or how or even when. i mean, i have talked to my family about it, because family will never let you down. but it still worries me, however, im just got sure.. im no doctor.
shes always been really skinny.. about 5 11 and probably under 120. im worried about her though, because i have noticed that she only eats crap food.. like cookies, cakes, sweets. no actual real food, and i have also noticed that i can not only see 2 ribs but now 4. i just dont know what to do.

ah, the age old question..
sit down with them and just start off by saying "is there anything you wanna talk about..i've noticed you've been acting different"..it can go off into you saying that you are worried about their eating habits...just don't push the matter too much. if they at least listen to what you are saying, at least you have planted a seed in their heart...with time, they'll come to you..just let them know that you are there..you wanna talk...but you want to listen more. a person with the disease is going through so much mental torment..just be careful, dont rush things..but keep an eye on them. best of luck and God Bless...