I am of long life
What I eat:
One of my foods is deadly to you
Another food is healthy for you in small quantities. However, it is in a way necessary for your daily life activities
My most important food, you cannot eat, but is indispensable to both of us
I don't eat exactly like you do (guess that is pretty obvious, he he)
This is my first one, so it might be really easy, but if not, don't hesitate ask for hints.
Cheers : )