Keep an eye on all that leftover squash casserole and sweet potato souffle in the fridge. It would be a shame if it went bad, because Americans waste a staggering amount of food every year. Nearly 40 percent of the food supply is wasted in the United States alone, according to a new study, published in the journal PLoS ONE. Researchers Kevin Hall and Carson Chow 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