Poor people have it, rich people need it, and if you eat it you will die. What is it?

Explanation

The word “nothing” fits every part of the riddle. Poor people often have nothing, rich people feel they need nothing, and if a person literally eats nothing, their body cannot survive. For example, if someone refuses to eat for many days and takes in nothing at all, they eventually become weak because the body needs food to stay alive. This is why nothing is the only answer that matches every clue in the riddle.