(In reply to A Guess
by K Sengupta)
The last line suggests, that the answer may be a poisonous food
substance , or it is equally probable that the answer is related to an absence of food.
The former theory is not reinforced in terms of the 3rd and 4th line, while in consonance with the thir line, it is true that the rich
have quite a lot of money, what they do not have is an absence of money at any given point of time, while the poor have very little money and will almost certainly experience a total absence of it at some point of time.
Thus, the 3rd through 5th line suggests, "nothing" as the common theme that connects them.
This is in consonance with the first and the second line, and
accordingly, the required answer to the given riddle is "nothing".