On Friday, June 11 this blog featured two postcards from the Imperial War Rooms which were replicas of public service posters from WWII. One encouraged citizens to use potatoes instead of bread: "Save bread and you save lives. Serve potatoes and you serve the country." A few readers speculated that the use of potatoes over bread might have something to do with the additional resources needed to produce and process wheat or referenced food shortages and bread lines.
One reader provided a link to a BBC article on rationing in Englad during WWII. It doesn't say why goods were in short supply, but it is an interesting description of what was rationed and how rationed goods were distributed.
Another reader provided a link to a NY Times article from WWI, announcing Hoover's request for voluntary reductions in wheat consumption due to the need for a steady supply of bread for soldiers, the stockpiling of wheat by pro-German sympathizers, and the hoarding of wheat by wheat brokers/profiteerers hoping for prices to go up. She speculates that the same dynamics were occurring in WWII.