The change in Elie when he reaches the concentration camp is shown through his attitude to food. At first, when he reaches Auschwitz, he reports refusing his ration of soup, even though he was very hungry, because he was "still the spoilt child." However, when he arrives in Buna, he reports that his whole life was dominated by the thought of his daily ration of food:
At that moment in time, all that mattered to me was my daily bowl of soup, my crust of stale bread. The bread, the soup--those were my entire life. I was nothing but a body. Perhaps even less: a famished stomach. The stomach alone was measuring time.
Note how Elie describes how his entire life had shrunk down to nothing more than a "famished stomach." It is that alone that is used to "measure time." He presents himself as a character stripped of all hope, dreams and plans, and is nothing more than a disembodied stomach that seeks to satisfy its hunger by any means possible. This shows the dehumanisation experienced by those in concentration camps that is witnessed in numerous places in this disturbing account of what life was like for a prisoner in a concentration camp. Relating this to Maslow's Hierarchy of Needs, Elie and the other prisoners have had every level taken away from them, and struggle to meet even their most basic human needs of food and protection.