Because we’re all fatter, I guess.

CHICAGO (AP) - Want to spend less at the pump? Lose some weight. That’s the implication of a new study that says Americans are burning nearly 1 billion more gallons of gasoline each year than they did in 1960 because of their expanding waistlines. Simply put, more weight in the car means lower gas mileage.

Using recent gas prices of $2.20 a gallon, that translates to about $2.2 billion more spent on gas each year.

“The bottom line is that our hunger for food and our hunger for oil are not independent. There is a relationship between the two,” said University of Illinois researcher Sheldon Jacobson, a study co-author.

“If a person reduces the weight in their car, either by removing excess baggage, carrying around less weight in their trunk, or yes, even losing weight, they will indeed see a drop in their fuel consumption.”

The lost mileage is pretty small for any single driver. Jacobson said the typical driver - someone who records less than 12,000 miles annually - would use roughly 18 fewer gallons of gas over the course of a year by losing 100 pounds. At $2.20 per gallon, that would be a savings of almost $40.

Outside experts said that even if the calculations aren’t exact, the study makes sense.

“If you put more weight into your car, you’re going to get fewer miles per gallon,” Emory University health care analyst Kenneth Thorpe said Wednesday.

I’m a bit skeptical about the impact this is having.

The example notes that if the “average” driver lost 100lbs he/she would save about $40 in a year, burning 18 fewer gallons of gas.  Yet...how many Americans are actually 100lbs overweight?

If the average American drives 12,000 miles a year and getting 21.4 miles per gallon (according to numbers from September of 2001, which were the latest I could find) that means we’re burning about 560 or so gallons of fuel per year per driver.  Burning eighteen additional gallons a year is a 3.2% increase.

That’s going to vary quite a bit, though, considering that some of us drive quite a bit more than 12,000 miles a year (I’ve nearly put up that much in a month before) and not all of us get 21.4 mpg.  Some get more, some get less.  Also, the impact weight has on the amount of fuel you burn is going to vary by vehicle, I’d imagine.  Extra pounds probably aren’t going to matter as much if you’re driving a big GMC Yukon as opposed to a little hatchback or something.