Here's another thing to blame on Americans' expanding waistlines: Fat people use more gasoline.

That's the conclusion of a study out of the University of Illinois at Urbana-Champaign, which says 938 million gallons of gas go into vehicles annually because drivers and passengers are considerably heavier than in 1960.

"Our nation's hunger for food and our nation's hunger for oil are not independent," said computer science professor Sheldon Jacobson, who co-wrote the study scheduled to appear in an upcoming issue of The Engineering Economist.

The project, which looked only at noncommercial travel, was based on the simple fact that heavier cars use more gas.

"We took today's cars and driving habits, and substituted people of average weight in 1960," said co-author Laura McLay, who was a doctoral student working with Jacobson and now is an assistant professor of statistical science at Virginia Commonwealth University. "I was surprised at the impact."

In 1960, the average adult male weighed 166 pounds and the female tipped the scale at 140. In 2002, those averages were 191 and 164, according to National Center for Health Statistics.

Jacobson, who has done numerous studies of how engineering principles can be applied to health issues, said the research wasn't meant to be nagging.

"There are many health benefits for losing weight," he said. "An unexpected benefit is that we would use less fuel."

Any savings wouldn't be significant, said John Felmy, chief economist for the American Petroleum Institute. "It's an interesting calculation," Felmy said. "But we use about 140 billion gallons a year. The savings would be less than 1 percent."

A representative of the Southern California Automobile Club, which has long preached that changes in driving habits can dramatically reduce gas consumption, said the human weight factor is far overshadowed by others.

"The difference between someone who diets and someone who doesn't is not much," said the club's chief automotive engineer, Steve Mazor, "compared to the golf clubs you put in the trunk."