In seeking to show that population growth threatens to exhaust the world's agricultural resources, the Worldwatch Institute has pointed out that in 1988, for the first time in its history, the United States ate more food than it grew. (b) If official trade accounts show that U.S. food imports exceeded food exports in any given year, this will mean that the dollar value of the imports was greater than the dollar value of the exports. Why would such figures not be persuasive evidence that the United States had lost the ability to feed itself