reply to post by Dr Expired
You're assuming that any alien that shows up will be even remotely biologically compatible such that it/they could metabolize anything on earth,
There's lots of things on this planet, that are native to earth, that we people of earth can't even metabolize.
Not every bit of earth life can be eaten by other earth life.
How then would it even be remotely logical for some other form of life that's evolved on an entirely foreign biosphere and environment to be capable
of eating even the most mundane and safe of earth foods?
Lettuce to aliens could be deadly toxic universe killing poison.