Whether you're in Manhattan or Montana, a visit to the local shopping mall reveals one painfully obvious fact: Americans are fatter than ever. Obesity-related illnesses and complications are now responsible for nearly one-tenth of the nation's annual health-care costs. It's therefore vital to understand what's behind our country's "obesity plague" and how best to solve this major public-health problem. Health economics can help on both fronts.

The rise in obesity is attributable primarily to changes in the price of consuming, and the cost of expending, calories—changes that are byproducts of otherwise beneficial technological advances.

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