binge eating

i was watching this show about binge eating...what i do not understand is, how do they get thin by eating so much!? and how can they keep eating? i know its a psychological disease, as is anorexia...i just...i cant comprehend how someone can eat so much? look at this little girl in the video, she ate all that??? i believe there is a comfort in just going crazy and eating as much as you possibly can stuff in your belly, and then hopefully puking/purging it all out...ughh....sad...