Our food system churns out enough to provide every man, woman, and child with 3,800 calories a day. But only 2,550 of those calories get eaten. With 70 percent of adults and 35 percent of children overweight or obese, we’d be better off eating even less. Even so, those 1,250 wasted calories lead to greenhouse gas emissions, thrown-away resources, and higher prices. What can we do?