Ken Rogoff and David Ludwig have a piece in the New York Times detailing how obesity is such a cost to us all that something must be done. They make a mistake which Rogoff, being an economist and a good one to boot, should know not to make. He fails to look at opportunity costs and thus believes that obesity costs healthcare systems money.

This is not true, obesity saves money. Obesity reduces the costs of running the healthcare system (and pension and retirement systems) precisely because it does indeed kill people.