U.S. scientists have come up with another reason for obese people to lose weight -- excess driver and passenger weight results in excess fuel consumption.

In a 2006 study, University of Illinois Professor Sheldon Jacobson and doctoral student Laura McLay estimated the amount of vehicle fuel consumed as a result of overweight and obese passengers.

Now Jacobson and doctoral student Douglas King have updated the estimates of weight-based fuel consumption and compared them with those reported in 2006.

They said the results aren't good news.

"Growing overweight and obesity rates in the United States continue to increase fuel consumption by adding extra passenger weight to vehicles," said Jacobson. "More than 1 billion gallons of fuel consumed each year can be attributed to this excess weight."

In 2006, Jacobson and McLay found cars and light trucks consumed up to 938 million additional gallons of fuel each year as a result of average weight gain that had occurred since the 1960s. In the new study, Jacobson and King found the amount of additional fuel had jumped by nearly 200 million gallons, to 1.137 billion gallons a year, an increase of about 21 percent.

The study has been accepted for publication in the journal Transport and Environment and posted on its Web site.