do the prisoners fast yom kippur? why ?

This happens after Elie and his father have been moved to Buna. Elie states,

"I did not fast. First of all, to please my father who had forbidden me to do so. and then, there was no longer any reason for me to fast. I no longer accepted God's silence. As I swallowed my ration of soup, I turned that act into a symbol of rebellion, of protest against Him. And I nibbled on my crust bread.