Because I am clever and quick on my feet, I of course answered right away: "Buh?"
When we go on vacation, people often tell us to be careful what we eat or drink, because our stomachs might get upset. So what would it be like going to another planet?
Everything we eat is current or former living matter, with the possible exception of that cheese stuff that comes in a spray can. Anyway, it all (is/was/came from) a living thing, and all of it is native to Earth. If we went to an alien homeworld and scarfed down a Blargburger-with-splenge(TM), the bacteria in our guts might not have the faintest clue what to do with it.
(top row) Blargberger with splenge
(bottom row) Splengeburger with blarg
Not my image. I got it from Pinterest. No idea where they got it.
Perhaps they've developed something new. People around here talk about so-called 'superfoods', like kale, or quinoa, or (in my case) pizza. Maybe the aliens have developed a One Perfect Food that satisfies all their nutritional requirements, tastes awesome, and is made in an environmentally-sustainable food extruding apparatus.
Maybe it comes in a spray can. I'd try it.