A new study reveals that US life expectancy is falling even further behind other industrialized countries. As of 2007, the life expectancy of Americans is 75.6 for men and 80.8 for women, which puts us in 37th place internationally. On average, Americans live three years less than citizens in the top ten longest-lived countries, and those countries pull further ahead of us every year.

Or rather, those countries pull further ahead of some of us every year. The study also reveals huge disparities along racial and geographic lines. Some counties in the U.S. have third-world-level life expectancies as low as 65.6/73.5 while others rival low-mortality nations like Japan with life expectancies as high as 81.1/86.0.

At first blush, one might be tempted to blame our inequitable health care system for these dramatic disparities. The explanation has intuitive appeal. The health care system is designed to save lives. If people die younger in some places, it must be because they have poorer health care.

But what if the difference does not lie in any failure to save lives? What if people in some counties are just sicker?

Let's start at the international level. In what way does the US stand out among other industrialized countries when it comes to physical health? Easy. We are the fattest country on Earth. By far. 30.6 percent of Americans are obese. Among the long-lived Japanese, only 3.2 percent are obese. Among our Canadian neighbors, who outlive us by about three years, 14.3 percent are obese.

There is a well-established causal relationship between obesity and mortality, so the correlation does seem significant, but the international metrics are crude measures. Can we find a correlation at the county level?

Here is a representation of life expectancy by county as concluded by the new study:

Notice the long-lived regions in the Northeast, Midwest, West Coast, South Florida, and Hawaii. Contrast them to the red crab-claw shape that extends across the South from Louisiana to the mid-Atlantic.

And here is a representation of obesity by county:

See any similarities?

While the American health care system is certainly plagued by inequality and other problems, the data suggests that when it comes to mortality, the fault is not in our health insurance but in ourselves.

The good news is that the drafters of last year's health care reform were aware of the problem. Below the storm over insurance mandates and those mythical "death panels," the act required federal agencies to draft a plan to improve Americans' health outside the hospital.

In accordance with the requirement, the Obama Administration today released the National Prevention Strategy, which aims to reduce smoking, obesity, alcoholism, and other unhealthy behaviors.

The bad news is that the most of the strategies consist of unenforceable guidelines and vague recommendations to business and communities like, "Increase access to healthy and affordable foods in communities," and, "Help people recognize and make healthy food and beverage choices." Thanks for the tips, Mr. President.

The health care law does include $17 billion in local grants to support prevention programs, but don't expect it to make much of a dent in national life expectancies.

Obesity remains stubborn problem that no amount of recommending or cajoling is likely to solve. Unless governments get serious about limiting access to fatty foods and drinks through taxation and regulation, the US will remain the fattest country in the world with a shamefully high mortality rate.

Update: Reader Lamont has corrected my international obesity figures, which date back to 2002 and 2003. According to the latest data, Mexico has topped the US as the world's fattest country. Australia, which was nine percentage points behind us in 2002, is only three points behind us now. That contradicts the obesity hypothesis because Australians have significantly higher life expectancies than Americans.

But as it happens, my old data is actually more relevant. The relationship between obesity and life expectancy is delayed. Obesity today won't significantly impact life expectancy rates for years. So if anything, my data is too recent.