One of the most ambitious assessments yet of our global food system calculates the health, environmental, and economic losses of business as usual. It also outlines what governments can do to reap trillions of dollars’ worth of benefits by producing food more sustainably. All in all, the damages caused by the current system — how food is produced, marketed, and consumed — add up to $15 trillion in losses a year. That includes health costs associated with poor nutrition, biodiversity loss, climat...