Editor's note: This is part of an occasional series on financial what-ifs.

In the United States today, 66% of adults are overweight. Almost 33% of adults are obese, and 4.7% are morbidly obese, or more than 100 pounds overweight. But . . .

What if nobody in America were fat?

We'd save billions of dollars in gas. Airlines would double their profits. A dearth of diabetes and other diseases would save billions of dollars more -- and put thousands of doctors on the street. McDonald's would sell not Big Macs but little steamed chicken snacks -- or watch its profits melt away. Productivity would rise, potentially creating tens of thousands more jobs or higher wages all around.

Add up the savings up on health, food, clothing and efficiencies, and you could buy a professional home gym for every U.S. household -- or hand each $4,270 in cash.

$487 billion in gas, sweat and stretch pants

First, let's put the meat on that $487 billion. The estimates below assume the average American adult is at least 20 pounds overweight, a figure nutritionists see as fair.

• Savings on fuel for cars and airlines due to their lighter loads would top $5 billion, according to industry studies. Researchers say each overweight driver burns about 18 additional gallons of gas a year, or just under a billion gallons altogether. Savings in the air are far greater: The jet-fuel savings alone could double North American airlines' forecast 2008 profits to $3.8 billion and maybe persuade them to stop stranding passengers because they can't afford the fuel for flights. As for oil imports, they'd be dented by less than 1%.

• Plus-sized clothing costs 10% to 15% more, so shoppers would save $10 billion on shirts, pants and dresses. And clothes might fit better too. Cynthia Istook, an associate professor in textile apparel at North Carolina State University, says the economies of making fewer sizes would be tremendous. Clothing makers could then afford to offer more variety in hip and bust sizes, rather than asking every woman to squeeze into an hourglass shape.
• Because 3,500 calories translates into a pound of fat, somewhere along the way, America's 227 million adults have eaten 16 trillion calories too many. That's 14 billion Big Mac meals, with fries and a soda. Eliminate those and you wipe out $81 billion, or McDonald's past four years of sales.
  • If Americans were slim and maintained their weight by eating 150 fewer calories a day (half a slice of pizza), that could snip roughly 6.5%, or $20 billion a year, off U.S. farmers' sales (assuming no extra exports). Bob Young, the American Farm Bureau's chief economist, says farmers would cope. They'd switch some land from fattening seed oils and sugar beets to fruits and vegetables. Or they might grow corn for ethanol, or even open a hunting resort.
• • The medical costs of obesity-related problems such as diabetes, stroke and heart disease run near $140 billion, or more than 6% of all health-care costs. That ballpark figure was calculated by Joel Cohen, an economic researcher for the Agency for Healthcare Research and Quality, using data from a 1998 Centers for Disease Control and Prevention study. Cohen reckons that if no one were fat, medical insurance costs would fall -- to everyone's delight -- and doctors and drug makers could do more preventive care. That sounds good, but Roland Sturm, a senior economist for Rand in Santa Monica, Calif., doubts anyone would pay for preventive care. More likely, he says, some doctors would be on the street. "They could drive cabs," he suggests.
  • Productivity in the workplace would jump as people took fewer sick days and spent less time at work feeling unwell. Ross DeVol, the director of health economics at the Milken Institute, says the loss of productivity due to people showing up at work sick is "immense." Using a recent Milken report on the subject, he calculates that if no one were obese, the added output from workers and their caregivers would give the country a $257 billion boost. That's 1.8% of GDP, enough extra output to allow businesses to hire tens of thousands more workers or to raise wages, economists say. Or at least, that's the theory. Given bosses' love of expanding their profits and their own pay, you can count on some of this being spirited away. Just look at 2000 to 2005, when worker productivity rose 16.6% while median wages rose less than half that amount.
  • "Jenny Craig would be very unhappy" if everyone were slim, says Rand's Sturm. And so she would, along with the rest of the $55 billion weight-loss industry. Trimmed-down citizens would be swapping their diet pills for bikinis and their gastric-banding for nose jobs.

What to do with all that money?

On top of these savings would be billions of dollars more. Manufacturers and builders wouldn't have to make doorways bigger, car seats wider, furniture stouter. Some even argue that global warming would slow a mite, as consumption of gas, energy, fertilizer and methane-producing cattle decreased.

Even without those extras, the $487 billion reshuffle of the economy would put us on the spot. Exactly how would we spend all this freed-up cash? Optimists sing about improving education or medical research. Others figure we'd fritter away the money.

It seems, in fact, that economists have a word for our usual behavior: suboptimal. That's what we do. We suboptimize. We think short term instead of long term, reducing our chances of living healthily and happily ever after.

So assuming we didn't behave like angels, the net effect on the economy of a slimmer population would be a lot of reshuffled resources, with a nice rise in productivity that should take our living standards up a notch.

The social gains are more difficult to predict. Research has shown that people who are not obese marry more, are paid more, are promoted more, sleep better and have better sex lives. We don't yet know whether people earn less because they're fat, or whether they're fat because they earn less. Researchers suspect it is the former because there's some evidence of discrimination against the obese.

Either way, a slimmer society would, arguably, seem to be more secure and content.

But, of course, then we have the awful question: Can we all be paid more and promoted more and marry more? Only to a limited degree.

Jay Zagorsky, a sociology researcher at Ohio State University, is convinced that society would adjust. We might lose an awful lot of people to pick on, but he concludes: "They will find something else. If it's not the size of your waist, it may be the size of your nose."

Published April 23, 2008

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