The Associated Press

A new study suggests that Americans are burning nearly four billion more litres 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.

"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 co-author of the study.

"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 19,000 kilometres annually — would use roughly 68 fewer litres of gas over the course of a year by losing 100 pounds.

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," Kenneth Thorpe, a health care analyst at Emory University, said Wednesday.

2 out of 3 Canadians overweight: StatsCan

The same effect has been seen in airplanes. Research from the U.S. Centers for Disease Control and Prevention found that heavy fliers have contributed to higher fuel costs for airlines.

The obesity rate among U.S. adults doubled from 1987 to 2003, from about 15 per cent to more than 30 per cent. Statistics Canada estimates that two out of every three adults in Canada are overweight or obese.

The study's conclusions are based on those weight figures and Americans' 2003 driving habits, involving roughly 223 million cars and light trucks nationwide.

It will appear in the October-December issue of The Engineering Economist, a peer-reviewed journal published by the American Society of Engineering Education and the Institute of Industrial Engineers.

Researchers found that estimated that nearly 148 million litres of fuel are used each year for every additional pound of passenger weight.

The amount of extra fuel consumption blamed on weight gain since 1960 would fill almost two million cars with gas for an entire year. However, that is only 0.7 per cent of the total amount of fuel consumed by U.S. passenger vehicles each year, Jacobson said.