As rising gasoline prices are forcing many Americans to tighten their financial belts, it may lead to them tightening the belts around their waist.

"An additional $1 in real gasoline prices would reduce obesity in the U.S. by 15 percent after three years," said Charles Courtemanche, an economics researcher at Washington University in St. Louis. "In fact, about 13 percent of the rise in obesity between 1979 and 2004 can be attributed to falling real gas prices during the period."

Courtemanche's conclusions are based on a comparison of average state fuel prices with health behavior trends documented in government surveys covering two decades, 1984-2004. He provided evidence for two direct and causal links between gasoline prices and obesity.

"If the price of gas rises, the cost of driving also rises, which may affect body weight in two ways," Courtemanche said.

The first, he said, may lead people to drive less, leading to more exercise like walking or bicycling.

"If a person uses public transportation, such as subways, buses, trolleys, or rail services, the need to move to and from the public transit stops is likely to result in additional walking, again decreasing weight," he said.

The connection, he said, may lead people to eat out less, since the cost to drive to the restaurant is increased.

"People may substitute from eating out to preparing their own meals at home, which tend to be healthier," he said. "People may also eat out less in an effort to save money to pay for the increased cost of gas."

Courtemanche's study, "A Silver Lining: The Connection between Gas Prices and Obesity," touched off a lively debate in online economics groups this summer when findings from his working paper were cited in article published in The New York Times.

Some suggested that Courtemanche was politically incorrect to suggest a gasoline tax as a means of addressing a larger societal problem, such as an individual's obesity. He said he didn't mean to imply that additional gasoline taxes would be good for society, "just that additional gasoline taxes would reduce obesity."

Courtemanche said that his current study makes no attempt to determine if increased fuel costs would have a positive or negative net impact on social welfare.

"Research shows that reducing people's incomes would worsen obesity, so any increase in the gasoline tax should be accompanied by mass transit subsidies, payroll tax reductions, or some other policy that replaces the lost income," he said.

According to Courtemanche's analysis, the reduction in obesity caused by a $1 increase in gasoline prices would save 16,000 lives and $17 billion a year.

Despite the fact that eating and exercise are personal choices, intervention may be justified because an individual's obesity may have a negative impact on society, he argues.

"With obesity, the most obvious negative externality is medical expenses," he said. "Because of public insurance (Medicare and Medicaid), the medical expenses of obese people are often paid for by taxpayers. For people with private insurance, their medical expenses increase everyone's premiums."

"Again, that doesn't necessarily mean the gas taxes are the best policy," he said, "just that some obesity-reducing policy may be appropriate."