I got a letter in the mail..(how do they know all this information) ?

I got a letter in the mail today for an offer to do " plus size modeling". 1) That is offensive. 2) How do they know my body shape and size? ( This is damaging on so many levels, I do not shop in plus size, nor do I need to, but I am a teenage girl and this kind of stuff could (it won't but hypothetically) turn me to be bulimic or anorexic, is this even allowed?)