The concept of a "hunger artist" is real and something that does exist.  This was the realm of professional fasting, whereby individuals fasted and there was a public fascination with it.  Yet, I think that Kafka is striving to make a larger statement about how the artist can become trapped with the public voyeurism into the creation of their art.  In this sense, Kafka is making the argument that there is a certain trapping of fame and this is something that creates the cage that binds the artists.  Kafka is arguing that the hunger artist is one that is trapped by the perception of others and the outside world.  In this, the hunger artist is one that is not in control of his art, but rather find himself controlled by either the art or the public fascination with it.  Kafka's conception of the hunger artist is really enhanced with the advent of reality television and the constant presence of the web.  He seems to be ahead of his time in sensing that the modern artist is one ensnared in a cage whereby others view him in the most sensationalist of ways.  Art is sacrificed to sensationalism and notoriety, or even this becomes the art.  In this way, the modern hunger artist is one that no longer travels in a carnival, but rather is around everywhere, indicating that the freakshow is actually what is seen as "normal" society.  In this, Kafka has taken a historical reality that actually existed and made a metaphor out of it.