What's making us fat?

CALL IT Fattergate. Americans are getting scandalously big for their britches (and shirts and skirts and dresses and suits). And scientists would like to know why, so they can make it stop. After all, this sharp trend toward a well-rounded population has some pretty hefty (and heinous) consequences for public health.

There's a simple explanation for the weight gain, of course: People consume more calories than they burn. The favorite explanation: They eat bigger portions of less nutritional foods at easier-to-get-to fast food places, even as they hunker down more and more faithfully in front of their TV and computer screens. "Most of us say it is a combination of reduced energy expenditures plus dietary intake not declining enough," says Barry Popkin, a nutrition professor at the University of North Carolina at Chapel Hill.
But why does that happen far more often now than 30 years ago? It's not obvious, says Susan Roberts, a senior scientist at the Human Nutrition Research Center on Aging at Tufts University in Boston: "There is definitely no definitive answer on 'what went wrong.' "

Even as researchers try to refine the eat-too-much-move-too-little theory, some are entertaining other ideas (obesity virus, anyone?). Read on for some of their theories, as well as a weigh-in from our panel of obesity researchers.