Followup: How much energy is wasted hauling around U.S. body fat?

April 27, 2012

Dear Cecil:

Recently someone asked about the amount of energy Americans are storing in body fat. A more pertinent question is how much energy is wasted hauling that fat around. Cars, planes, and trains have to burn extra fuel to move the excess pounds. How many barrels of oil would America save if not for all that lard?

Cecil replies:

Good point, Scott. Considered individually, the cost of hauling Joe and Mary Chub from point A to point B is relatively small, and in fact could have a positive socioeconomic impact if airlines, for example, were to wise up and charge by weight. From a macro perspective, however, we need to realize Americans collectively are carrying an extra 4.6 billion pounds of fat, one more reason the lean, hungry nations of the world are gaining on us fast.

Getting a handle on what fat drayage costs us is a bit of a project. According to a study sponsored by the Aluminum Association, a 20 percent reduction in a small car’s weight can result in a 10 percent increase in fuel economy. However, clearly what the aluminum people had in mind was making cars out of lighter materials (presumably aluminum), not getting the occupants to lose weight. A typical small vehicle weighs 2,900 pounds, so a driver carrying an extra 20 pounds adds less than 1 percent to the car’s overall mass.

That doesn’t tell you the whole story, though. A 2009 paper by the environmental research group Resources for the Future suggests fat drivers tend to buy fat cars — that is, ones that are larger and less fuel-efficient. The authors estimate that if overweight and obesity rates had stayed at 1980 levels — 20 percentage points lower than now — consumers in 2005 would have bought vehicles whose fuel economy on average was 1 MPG better than the ones they did. This is useful information. Rather than scolding people for buying SUVs because they’re bad for the environment, one might more effectively advance the argument that an SUV proclaims the owner is a blimp.

Getting back to fuel mileage, another 2009 study found that a one-pound increase in the weight of the average car occupant drives up gasoline demand by 40 million gallons per year. To put that in perspective, the researchers calculated that Americans during the Bush II era used an extra 473 million gallons of gasoline each year compared to their predecessors during Bush I, 758 million more than the unhappy ex-hippies of Carter's day, and 1.1 billion more than the trim veterans of the Eisenhower epoch. Imposing as all that sounds, however, we’re only talking about 1 percent of gasoline consumed by U.S. autos.

In search of more frightening statistics, we turn to a transportation mode where weight really matters — flying. The Centers for Disease Control put the average weight gain of American adults from the early 1990s to 2000 at 8.5 pounds for men and 11.4 pounds for women. Hurling that bulk through the skies meant burning an additional 350 million gallons of jet fuel costing more than a billion dollars annually.

There are safety issues to consider as well. In the wake of a 2003 plane crash where a suspected factor was excess passenger weight, the FAA ordered airlines to assume an extra 10 pounds per occupant when estimating aircraft loads. All that having been said, 350 million gallons isn’t really that much extra fuel burned — roughly 1.3 percent.

Let’s try greenhouse gas emissions. Yet another 2009 study considered how much extra energy is needed to sustain a fat populace versus a skinny one. Comparing typical average weight distribution in 1970 to now (body mass index 25, 4 percent obesity rate then; BMI 29, 40 percent obese now), the researchers calculated that a hypothetical population of 1 billion fat adults contributes to global warming as follows:

  • 270 million more metric tons of greenhouse gases stemming from extra food production needed for the 19 percent more calories we’d be eating overall.
  • 170 million tons of gases due to increased auto fuel consumption.
  • 2 million tons for extra plane fuel.

These are low-end numbers. If one assumes obese people mostly live in developed countries using more energy per capita, obesity results in as much as 1 billion extra tons of greenhouse gases per billion population annually. This gives us the desired conclusion: fat people, by their very existence, are imperiling the planet.

There’s more. The animals and plants required to produce the additional food consumed by an overweight population also boost emissions — worldwide production of animal feed contributes 18 percent of GHG, more than all forms of transport. Larger people require larger clothes and often larger furniture, cars, homes, and offices, and that means more GHG too.

Finally, a recent George Washington University study assessed the annual per-person cost of obesity as $4,879 for women and $2,646 for men, mostly due to higher medical costs and lost job opportunities. So listen to what science is telling you, America: don’t be fat.

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References

Casadei, Anrico and Broda, Richard “Impact of Vehicle Weight Reduction on Fuel Economy for Various Vehicle Architectures” Research Report, Conducted by Ricardo Inc. for The Aluminum Association Project FB769, RD.07/71602.2, 2008.

Dannenberg, Edward L. et al. “Economic and Environmental Costs of Obesity: The Impact on Airlines” Am J Prev Med 27.3 (2004): 264.

Dor, Avi et al. “A Heavy Burden: The Individual Costs of Being Overweight and Obese in the United States” The George Washington University School of Public Health and Health Services Department of Health Policy 21 September, 2010.

Edwards, Phil and Roberts, Ian. “Population Adiposity and Climate Change” International Journal of Epidemiology 38 (2009): 1137–1140.

Jacobson, Sheldon H. and King, Douglas M. “Measuring the potential for automobile fuel savings in the US: The impact of obesity” Transportation Research Part D 14 (2009):6–13.

Li, Shanjun; Liu, Yanyan; and Zhang, Junjie. “Lose Some, Save Some: Obesity, Automobile Demand, and Gasoline Consumption in the U.S.” Resources for the Future: Discussion paper RFP DP 09-33 August, 2009.

Powles, John. “Commentary: Why diets need to change to avert harm from global warming” International Journal of Epidemiology 38 (2009): 1141–1142.

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