Gas and grease are longtime guilty pleasures of Americans, but research now shows expanding waistlines are partly to blame for our rising bills at the gas pump.

Two University of Illinois researchers estimate that as many as 1 billion gallons of fuel are consumed each year in the United States due to excess weight in the American population.

The recently published study in the journal Transportation Research Part D: Transport and Environment says between 734 million and 1.104 billion gallons of fuel could be saved annually through improved fuel economy if weights of all overweight, obese and extremely obese Americans could be reduced to their maximum normal body mass index. Quantitatively, that's a large volume of fuel, but compared to the 75 billion gallons consumed by passenger vehicles each year in America, it's a relatively small percentage.

The researchers, computer science professor Sheldon Jacobson and doctoral student Douglas King, modeled this relationship between obesity and fuel usage by combining BMI statistics of the American population with data on noncommercial vehicle use, passenger demographics and fleet fuel efficiency. An earlier study of theirs reported at Miller-McCune.com had come to similar conclusions, and, as predicted, this latest research just shows the problem is getting worse.

Jacobson and King recognize that the 1 billion gallons of gasoline translates to only about 0.8 percent of the fuel consumed annually by noncommercial passenger vehicles in America; however, this small amount equates to approximately 9.71 million metric tons of carbon dioxide released to the atmosphere each year. That's equivalent to taking 1.7 million passenger cars and light trucks off the road for a year.

As socioeconomic problems, high fossil-fuel consumption and rising obesity rates are often considered separate issues, but Jacobson and King's research pinpoints an inherent connection between the two. While Americans are currently enjoying their reprieve from $4 a gallon gas prices seen this summer, past research suggests a steady and maintained increase in fuel prices could render a reduction in obesity rates.

In 2008, Charles Courtemanche, an applied microeconomics researcher at University of North Carolina at Greensboro, estimated that a $1 increase in average gas prices would reduce obesity rates by at least 7 percent over a seven-year period. Theorectically, elevated driving costs would lead to better exercise habits through discouraged automobile usage and decrease the number of meals an individual eats at restaurants.

"If this prediction holds true, fuel consumption will be reduced by a twofold effect," Jacobson and King write in their article. "Passenger weights will shrink as obesity rates fall, while decreasing automobile use will reduce the number of miles each passenger is carried."

Who needs diets? Maybe we can just wait for gas prices to shrink our wallets and tighten our belts.