Washington, May 12 (IANS) The biggest public health enemy may very well be the one staple of modern life most Americans can't do without - the automobile. But it looks like obesity has been fuelling increased use of automobiles in the US since the 1950s.

"You can think of obesity as an energy imbalance," said Sheldon H. Jacobson, University of Illinois professor of computer science.

"People consume food, which is a form of energy, and then they expend it in their activities," the journal Transport Policy reports.

To analyse the link between obesity and vehicle use, Jacobson and students Douglas M. King and Rong Yuan looked at annual vehicle miles travelled per licensed driver as a surrogate measure for a person's total sedentary time, according to an Illinois statement.

Previously, Jacobson studied the effects of extra driver and passenger weight due to growing obesity trends in the US causing excessive fuel consumption. Jacobson said this new study reverse engineers the relationship between weight and driving.

"What we did before was based on physics: You add more weight to a vehicle, it consumes more gasoline, and we burn more gasoline on an aggregate level," he said.

"This then raises the question, 'Is the reverse true?' If we drive more, are we going to become heavier as a nation?"

After analyzing data from national statistics measured between 1985 and 2007, Jacobson discovered vehicle use correlated "in the 99-percent range" with national annual obesity rates.

"If we drive more, we become heavier as a nation, and the cumulative lack of activity may eventually lead to, at the aggregate level, obesity," he said.

"When you are sitting in a car, you are doing nothing, so your body is burning the least amount of energy possible," he said. "And if you are eating food in your car, it becomes even worse."