A new estimate says that of 378 metropolitan areas, many could actually exist on locally grown food - if the local area is up to 200 miles away, which means New York City could claim farms in Delaware, New Jersey, Pennsylvania, Rhode Island, Massachusetts, and Connecticut are local to New York.
Even then, diets would have to change, because progress has meant having diversity and choice, and if locally-grown were really necessary, the population would starve along the Eastern Seaboard and the Southwest of the U.S. And meat would only be for the rich.