If America is at war with obesity, then obesity is winning. Three out of 10 adults are obese—72 million people with a condition associated with diabetes, heart disease, some cancers and other chronic illnesses. The belt-busting American waistline is becoming as much a political as public health question—and if some politician hasn’t already introduced the No Buffet Left Behind Act, he will after this week’s big “Weight of the Nation” report from the Centers for Disease Control and Prevention.

It’s almost quaint that government hasn’t tried to do more to deter weight gain. Perhaps it’s because the politics of fat are not easily digestible: Unlike traditional illness, obesity is largely the result of individual choices about diet and exercise. Still, maybe taxpayers really should care, given that they’re footing most of the medical bills.

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The singular feature of American obesity is its steep, out-of-nowhere rise. For most of the 20th century, U.S. obesity rates were stable, with a slight upward trend through the late 1970s. Suddenly, they spiked across all demographic groups and have continued to rise unabated. In sheer body mass, the entire population is heavier than it used to be, and the heaviest are much heavier. Just between 1998 and 2006, obesity rates increased by 37%, according to the CDC.

The costs are nearly as startling. In a study published this week in the journal Health Affairs, CDC researchers estimate that obesity now accounts for 9.1% of all medical spending—$147 billion in 2008. The Milken Institute estimates that chronic disease costs more than $1.2 trillion every year. On top of the medical resources devoted to preventable illness, a fatter and sicker work force is a drag on economic growth. In effect, we’re eating money.

Not to mention the entitlement programs, which pay for more than half of all obesity-related illness. The CDC puts the annual per capita increase in Medicare spending attributable to obesity at 36%. Medicaid comes in at 47%. An earlier Health Affairs paper notes that if the prevalence of obesity were merely at 1987 levels, Medicare spending would be at least $40 billion a year lower.