Disclaimer: I am fairly new to this; If I broke a rule or made a false claim just let me know and I can fix it ASAP!

This question is dealt with in Howard Smith's witness account, The Last Train to Berlin. Just as a pre-note, you must remember that the German people had suffered periods of massive inflation and unemployment rates (6million+) since the end of WW1, so shortages in resources were certainly not unheard of.

During the actual war, rationing of supplies began immediatly, although it started off as extremely livable. Smith notes that,"[f]or a people engaged in a life-and-death war ... the German people for two years of war ate amazingly well." This included 500g of meat per week, which was much better than the WW1 rationing under the Kaiser.

However, come Operation Barbarossa, this changed to 400g, and then dropped further, as significant rescources were expended with the Eastern advance. By late 1941, Smith writes, "for the first time ... the German people are undernourished", so I would say that is the point where the German people began to suffer for the war Hitler was waging.