So I m probably going through puberty or something, but I ve always been skinny, which is a good thing, and about 75ish lbs, and may I remind you I m almost 12. I can eat pretty much anything, then about thirty mins- hour later, I m hungry again. Fast metabolism? My doc hasn t said anything about me being underweight, but I do consider myself athetlic considering my dad and I go on bike trail rides often. I m about 4 11, if that helps.