After their biggest meal of the year, Americans might reflect on the fate of those moldering Thanksgiving leftovers. Nearly 40% of the food supply in the United States goes to waste, according to a new study, and the problem has been getting worse. “The numbers are pretty shocking,” says Kevin Hall, a quantitative physiologist at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) in Bethesda, Maryland. Food waste is usually estimated through consumer interviews or garbage inspections. The former method is inaccurate, and the latter isn't geographically comprehensive. 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 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. “We called it the missing mass of American food,” says co-author Carson Chow, a mathematician at NIDDK. In 2003, some 3750 calories were available daily per capita; 2300 were consumed, so 1450 were wasted, comprising 39% of the available food supply, the team reports in the November issue of PLoS ONE. This figure exceeds the 27% estimated by the U.S. Department of Agriculture (USDA) from interviews with consumers and producers.