What if we have it backward? What if the 310-pound man trying to jam into the middle seat and the 225-pound woman breaking into a sweat halfway up the stairs aren't the undisciplined miscreants of modern American life but the very emblems of it?
What if fatness, even obesity, is less a lurking danger than a likely destiny? What if the surprise isn't how many seriously overweight people are out there but how few?
Those are among the unsettling questions raised, at least implicitly, by "The Weight of the Nation," an ambitious multiplatform project that takes the full measure of our girth, its genesis and its toll.
A book with that title will be published next week by St. Martin's Press, and it boils down information from a more sweeping, four-part documentary to be shown next month on HBO, which produced it with input from the Institute of Medicine, the Centers for Disease Control and Prevention, and the National Institutes of Health. HBO also will make the documentary available on many websites, including its own.
Distilling many decades of research, "Weight" chronicles how we've eaten our way into disease and sometimes despair. About two-thirds of American adults now qualify as overweight or obese, according to the CDC.
But here's the scariest (and trickiest) part, which deserves much more attention than it has received and must be factored into our response: We may be doing nothing more or less than what comes naturally to us. Our current circumstances and our current circumferences may in fact be a toxically perfect fit.
Following in the heavy footsteps of "The Omnivore's Dilemma," "The End of Overeating," "The End of Food" and much else, "The Weight of the Nation" makes an especially persuasive case that gluttony isn't Americans' problem. Agriculture and abundance are.
Over the past century, we became expert at the mass production of crops like corn, soybeans and wheat -- a positive development for the most part.
We also became expert at feedlots for livestock and at processing those crops into salty, sweet, fatty, cheap and addictive seductions. This has downsides.
Densely caloric and all too convenient food now envelops us, and many of us do what we're chromosomally hardwired to do, thanks to millenniums of feast-and-famine cycles. We devour it, creating plump savings accounts of excess energy, sometimes known as love handles, for an imagined future shortage that, in America today, doesn't come.
"We're simply not genetically programmed to refuse calories when they're within arm's reach," said Thomas A. Farley, New York City's health commissioner. He is one of dozens of leading physicians, academicians and public-health experts who appear in "The Weight of the Nation."
John Hoffman, an executive producer of the documentary, told me: "Evolutionarily, there was no condition that existed when we were living with too much fat storage. We've only known a world of plenty for maybe 100 years. Our biological systems haven't adapted to it."
This is probably summed up best by Michael L. Power and Jay Schulkin in their book "The Evolution of Obesity." "We evolved on the savannahs of Africa," they write. "We now live in Candyland."
Our systems aren't just rigged to gorge. They're also rigged in many cases to rebound from weight loss and put pounds back on, as Tara Parker-Pope explained in a cover story for the New York Times' Sunday magazine last year. So we're fighting against that bit of nature, too.
Then there's this: The battle is perpetual and maddeningly nuanced.
"When it comes to smoking or drinking, people generally have to go cold turkey," notes David Altshuler, an endocrinologist and geneticist, in the documentary. "But fundamentally we have to eat."
Every meal is a surrender that can be only partial, a feat of calibration.
"We underestimate how hard it is to change your behavior not once -- not for a week or a month until you're cured -- but to change it every day for the rest of your life," Altshuler says.
If we're going to wage a successful war against unhealthy weight gain and obesity, we need to understand all of that. We need to stop vilifying obese people, who aren't likely to be helped by it.
And we need to rethink and remake our environment much more thoroughly than we seem poised to do.
The kind of consciousness-raising and corporate prodding being done by Michelle Obama -- laudable as it is -- won't be nearly enough. Neither will the extra green space for exercise that cities like Nashville have commendably created, or New York City officials' admirable exile of sugary sodas from public-school vending machines.
These important steps, plus others under consideration, are just the start. Let's move, yes. But let's do it a whole lot faster, because what we may be trying to hold back is a near inevitable tide.
Frank Bruni is a New York Times columnist. He chronicled his struggles with weight in the book, "Born Round."