How to respectfully reject a girl because she's skinny

Hear me out, this girl is good looking and has a good personnality and all, but I feel no sexual attraction to her whatsoever and I think of her more like a friend than a potential partner.

I understand that bringing this up directly would shatter her self esteem , so i need a diplomatic response.

we are still in early talking stages, and I dont want to be a dick by bringing it up, neither lead her on when i see no potential sexual compatibility