Advocates who want to reduce the use of fossil fuels through improved mileage for gasoline and diesel vehicles have a new target—human fat.
No, they're not talking some macabre new biofuel. They're simply pointing out that it takes more fuel for big-bellied, broad-butted Bubba to drive around in his full-size pickup truck than for skinny Minnie in her small economy vehicle.
"One socioeconomic implication of obesity is that it reduces passenger vehicle fuel economy," said Sheldon H. Jacobson, director of the simulation and optimization laboratory in the computer science department at the University of Illinois.
In 2006, Jacobson and doctoral student Laura McLay found US cars and light trucks consumed as much as 938 million gal/year of additional fuel due to the increased number of overweight and obese motorists since the 1960s.
In a follow-up study in 2008, Jacobson and doctoral student Douglas King found the amount of additional fuel escalated some 200 million gal to 1.137 billion gal/year, said a University of Illinois article on the web site, www.physorg.com.
Jacobson estimates more than 39 million gal/year of fuel are necessary to transport each additional 1 lb of average gain among US motorists.
Just as smaller, lighter alternative vehicles are coming on the market, US residents are getting bigger.
"Without taking into consideration the growth trend of overweight and obesity and its impact on vehicle demand, long-term government interventions are likely to miss the intended policy goals in reducing gasoline consumption and carbon dioxide emissions," said Shanjun Li, Yanyan Liu, and Junjie Zhang in a 2009 discussion paper for Resources of the Future, Washington, DC.
They said, "Our simulation results suggest that if the rate of overweight and obesity in 2005 had stayed at the 1981 level (20 percentage points lower), the average mpg of new vehicles demanded would have been 24.04 instead of 22.99. This implies a 4.6% saving in gasoline consumption over vehicles' lifetime."
Size offsets engineering
Obesity is offsetting automobile engineering for better fuel economy. The auto industry has a fuel economy target of 24 mpg for 2011 model light trucks that is expected to save more than 250 million gal/year of fuel. But according to Jacobson and McLay, that savings will be eliminated by increased fuel consumption due to an average weight gain of 6.4 lb among US residents.
A motorist who can barely squeeze his broad bottom into a booth at his favorite all-you-can-eat buffet isn't likely to shoehorn himself into a fuel-efficient mini-vehicle that looks like it might crumple like an aluminum can under his weight. Portly drivers are more likely to opt for full-size vehicles that provide more room and comfort. And even then, they may not click on seatbelts that aren't designed for people their size.
In addition to getting fatter, US residents also are getting taller, up an additional inch since the 1960s, Jacobson reported. "To address this, our new study looked at the distribution of body mass index, instead of the distribution of weight," he said.
CDC weighs in
The Centers for Disease Control and Prevention in Atlanta said in August the US overall estimated prevalence of obesity was 26.7%, up from 25.6% in 2007, 23.9% in 2005, and 19.8% in 2000.
CDC reported the prevalence of adult obesity ranged from 18.6% in Colorado to 34.4% in Mississippi. No state met the Healthy People 2010 minimal obesity target of 15%, but nine had obesity prevalence greater than 30%, compared with none in 2000.
US problems with obesity and fuel-dependency are so inner-twined "we cannot hope to tackle one without also tackling the other," Jacobson said.
"The growing obesity problem is a major symptom of our nation's addiction to oil. We prefer to ride when we should walk."
Nor is the problem limited to the US.
Jacobson cited "a recent surge in overweight and obesity rates in China" that he claims correlates with increased automobile ownership, indicating the problem will become international as more nations become affluent.
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