Erik Stokstad reports that a group of researchers has found that Americans waste about 40% of their food:
Food waste is usually estimated through consumer interviews or garbage inspections. The former method is inaccurate, and the latter isn't geographically comprehensive. [Kevin] Hall and his colleagues tried another approach: modeling human metabolism. They analyzed average body weight in the United States from 1974 to 2003 and figured out how much food people were eating during this period. Hall and [Carson] Chow assumed that levels of physical activity haven't changed; some researchers think that activity has decreased, but Hall and Chow say their assumption is conservative. Then they compared that amount with estimates of the food available for U.S. consumers, as reported by the U.S. government to the Food and Agriculture Organization of the United Nations. The difference between calories available and calories consumed, they say, is food wasted.
(Hat tip: 3QD)