Such is the scenario suggested by a new study projecting that 42 percent of American adults will be obese by 2030. That’s 32 million more than today’s 78 million. Of course, they probably won’t be waddling. They’ll be in their cars in the fast-food lane, as they are now. Recall that independent filmmaker Morgan Spurlock (“Super Size Me”) gained 24.5 pounds after one month of eating exclusively at McDonald’s.

Nothing less than a “major public health intervention” is needed, according to Eric Finkelstein, a health economist with the Duke University Global Health Institute and lead author of the study.

What this means is anyone’s guess, but it isn’t far-fetched to infer that a government-mandated health-care system eventually would necessitate a government-mandated diet to control costs. In another study, Finkelstein and the Centers for Disease Control and Prevention estimated that obesity costs about $147 billion per year, accounting for about 9 percent of all medical expenses. An obese person, defined as carrying an extra 30 pounds, costs about $1,400 more in medical expenses per year than a person of healthy weight.