I have a son that's 6' 3" and he is thin...could eat me out of house and home!!! And yes, I'd come in and find that he had already fixed the steaks that I was thawing for dinner and wondered what we were having for dinner!!! Some of his friends could make him look like he was snacking! Some people have a higher metabolism than others. The best thing your son could do is to work at a restaurant and get more food there.
About the lying...I always wanted my sons to tell me the truth no matter what. So they feel that they can tell me ANYTHING and now I wish I didn't know what I do! Does that make sense? Be careful what you ask for, you might just get it!
Swalker (covers ears sometimes! )