## Study: Weight Gain of US Drivers has Increased Nation’s Fuel Consumption

##### 01 November 2006

Researchers at the University of Illinois at Urbana-Champaign and Virginia Commonwealth University have concluded that the weight gain of Americans since 1960 has resulted in increased fuel consumption.

In a paper to appear in the October-December 2006 (Vol. 51, No. 4) issue of the journal The Engineering Economist, the scientists conclude that each extra pound of body weight in all of today’s vehicles results in an increase in gasoline consumption of more than 39 million gallons each year.

As a result, Americans are now pumping 938 million gallons of fuel more annually than they were in 1960 as a result of extra weight in vehicles. When gas prices average $3 a gallon, that results in additional aggregate expenditures of$7.7 million a day, or $2.8 billion a year. The numbers are added costs linked directly to the extra drain of body weight on fuel economy. The reason we looked at this issue was that gas prices hit an average exceeding$3 per gallon in September 2005. This was the highest recorded level in the United States. We thought there must be some way that we could determine how to quantify the effect of being overweight on fuel consumption. We felt that beyond public health, being overweight has many other socio-economic implications.

—Prof. Sheldon Jacobson, University of Illinois

Jacobson presented the challenge to Laura McLay, who was a doctoral student in his laboratory at that time and is now on the faculty at Virginia Commonwealth University, and they pursued the issue through his funding with the National Science Foundation.

Their conclusions are based on mathematical computations drawn from publicly available data on US weight gain from 1960 to 2002, a period in which the weight of the average American has increased by more than 24 pounds, according to data from the US Department of Health and Human Services.

By 2002, 62 percent of adults were overweight with a body mass index of between 25 and 30; more than 30 percent were considered obese with a BMI exceeding 30.

The fuel-consumption calculations apply only to passenger vehicles, including cars and light trucks driven for non-commercial reasons. Ruled out were other factors such as increasing the weight of cargo or decreasing fuel efficiency through poor maintenance. Driving data collected in 2003 were used to gauge fuel consumption based on weight gains during the last four decades.

The researchers used three different scenarios that considered not only heavier drivers behind the wheel but also their passengers, accounting for individual characteristics such as ages, numbers of people in the vehicle, and expected weights.

Since 1960, McLay and Jacobson said, the consumption of no less than 938 million gallons of gasoline annually can be attributed to weight gains of drivers and passengers. Of that total no less than 272 million gallons are consumed annually as a result of weight gains since 1988.

The key finding is that nearly 1 billion gallons of fuel are consumed each year because of the average weight gain of people living in the United States since 1960—nearly three times the total amount of fuel consumed by all passenger vehicles each day based on current driving habits.

Although the amount of fuel consumed as a result of the rising prevalence of obesity is small compared to the increase in the amount of fuel consumed stemming from other factors such as increased car reliance and an increase in the number of drivers, … it still represents a large amount of fuel, and will become even more significant as the rate of obesity increases.

The conclusions, Jacobson said, should be considered conservative because they do not consider many indirect consequences of obesity nor the increase in the number of vehicle miles linked to more people living in the United States and owning cars.

(A hat-tip to Rafael Seidl!)

No doubt extra weight causes the use of extra fuel but I have trouble with any study that uses BMI ... It's a load of crap. It doen't differentiate between fat and muscle. I'm 6'1", 230lbs giving me a BMI of over 30. According to BMI I'm actually obese! I have a 36" waist and swim 2k per day (Only a Canadian would mix imperial with metric). Sure, I could stand to loose about 15lbs, but I'm not obese.

Very few people will admit that they are over-weight but the facts remain that a very high percentage (the majority) of North Americans are either over-weight or obese.

One trillion gal/yr may not be much but if you add in all the extra energy consumed to produce and prepare all the extra food and drinks to get there, the over-sized cloths, extra wear and tear (shoes, tires, brakes etc) and all the extra medical cares and expenses required, the total extra energy and resources consumption may be 2 to 3 times as much as really required.

If you add the \$85/Ton for the extra GHG/CO2 produced by excess body weight + the extra air-conditionning + larger gas guzzlers etc etc, you may get..... some of the reasons why North Americans consume 2+ times the energy per capita than Europeans do.

My observation is that there seems to be a high correlation between heavy people and SUVs. Overweight people feel more comfortable in a larger car. Cramming themselves in a smaller car would just draw attention to your weight. I admit this is anecdotal but it would be interesting to see a study. It is not just about the weight of the person but the additional weight on the vehicle driven by the overweight person.

The irony is that if people would get out of their cars and walk more, they could save fuel two ways -- one way not using the car and the second way, using less fuel when they get in the car.

SUVs were sexier/cooler than big cars during the 90's. Sitting high above the traffic was also attractive.

Consume less
Emit less

Wow, take two disparate elements and try to draw a correlation...

How about this: The increase in average wages has caused an increase in fuel use. Track wages over the years and fuel use and then draw a correlation. I guess this concludes that we should make less money (because then we couldn't afford SUVs and wasting gas) to save fuel.

How about the studies conducted (by either NHSTA or IIHS) which showed that underweight and overweight people suffer more serious injuries in vehicular accidents and only those with slightly above average bodyweight suffered the least injuries. It was also found that the underweight people tended to suffer worse injuries than the overweight. The study focused on adults. I guess if you want to be safe in an accident you should focus on a BMI of around 25-27.

Personally, I'd have to go to extreme measures to get my bodyfat lower or lose muscle mass to get my BMI below the overweight area (5'11" 210).

Wow, take two disparate elements and try to draw a correlation...

Weight has nothing to do with fuel economy? Try again.

Sure, if we were talking about the weight of the vehicle... but when talking about the weight of the people:

20lbs of flesh in a 3000lb + vehicle will not make a difference in fuel economy that you could detect without precise laboratory equipment.

20lbs of flesh in a 3000lb + vehicle will not make a difference in fuel economy that you could detect without precise laboratory equipment.

Perhaps you should read the report instead of considering it to be as simplistic as you're characterizing it to be.

The point I made had to do with you claiming that weight and fuel economy are "disparate elements". Weight is a fundamental driver of fuel economy - exactly the opposite of your characterization that the study is somehow linking two things which have nothing to do with one another.

Personally, I'd have to go to extreme measures to get my bodyfat lower or lose muscle mass to get my BMI below the overweight area (5'11" 210).

The BMI for those dimensions is right on the border of obesity. It's hard to believe that it would take "extreme measures" to trim down from that size.

Track wages over the years and fuel use and then draw a correlation.

There is none.

Most of us 'Mericans would look much different and some might say unhealthy if we followed these charts. I scored a borderline overweight (never been accused of that) but I could see myself being leaner if I was more active. I guess these charts represent a balance between eating right and exercise.

BTW the BMI site I looked at

http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm#limitations

Clearly stated athletic people would have an overestimated BMI (never been accused of that before either!)

Pizmo,

Show where the report indicates that those who weighed the most also consumed the most fuel. If a given vehicle weighs more than the same vehicle would consume more fuel. If a 250lb person drives a Honda Civic and a 100lb person drives a Honda Pilot the Civic driver consumes less fuel for the same distance regardless of the Civic driver being heavier.

The data does not indicate whether or not heavier drivers choose vehicles which are less efficient it just draws a correlation between the weight of people and increasing use of fuel when they are disparate because a heavy person could very well drive a fuel efficient vehicle and a light person could just as easily be driving a hummer.

If you spend any time in the gym, lifting weights, you would understand that unless you are genetically gifted it would take extreme measures to get your bodyfat much below the 12-13% range while maintaining muscle and strength. I don't feel like sacrificing my health or significant amounts of time to do that as I have no desire to do so (I see no need to be below 12-13% bodyfat as I am not a bodybuilder or a model). Note that I said it would take extreme measures to get my bodyfat lower. I'm not about to purposely lose muscle mass that took years to develop (while maintaining my current level of leanness).

Show where the report indicates that those who weighed the most also consumed the most fuel.

Have you read the report yet? Yes or no? I haven't, nor am I defending its thesis. What I am doing is contesting your claim that weight and fuel economy are "disparate elements".

If you spend any time in the gym, lifting weights, you would understand that unless you are genetically gifted it would take extreme measures to get your bodyfat much below the 12-13% range while maintaining muscle and strength.

I've been lifting weights my entire adult life. If you spent any time reading up on BMI, you'd know someone who weighs 210 lbs and is 5'11" has a BMI of 29.3 -- right on the boundary of obese. My BMI is 22.5 -- right in the middle of the normal range. And I'm more than sufficiently strong.

I am not saying that weight is disparate from fuel economy in and of itself but the weight of the driver is if you are not comparing the same vehicle and even then the percentage difference in overall weight is not significant enough to impact fuel economy to a measurable degree. If the report had discussed the weight of vehicles increasing and consequently leading to an increase in fuel consumption I would not have any problems with it as that is true.

Your BMI is 22.5 and you say you are strong but that is relative to each person. What do you bench, squat, deadlift, clean & jerk, and snatch? What is your BF%? This information would tell me much more about you "physically" than your BMI. My BMI leads one to believe that I am close to being obese yet my waist is 33.5", and I can do an easy set of 5 reps at a little over double my bodyweight for squats and 3 reps at 1.5 times my bodyweight for benchpress...yet BMI indicates I am an unhealthy slob.

pizmo:

"The BMI for those dimensions is right on the border of obesity. It's hard to believe that it would take "extreme measures" to trim down from that size."

My point about BMI is that is that it's definition of obese is rediculously low for certain kinds of regular activity. No one has ever accused me of being anything more that a little overweight. When I was down to 195 due to illness my doctor told me to put on some weight to stay healthy. According to the BMI charts I'd have to weigh in at 185 to not be overweight. I'd be a rake at 185. My point is that BMI can't differentiate between muscle and fat. Swimming tends to put a lot of weight on the shoulders.

According to BMI Ian Thorpe (sure wish I swim like him) is "overweight" at a BMI of 27.4! ... give me a break

If the report had discussed the weight of vehicles increasing and consequently leading to an increase in fuel consumption I would not have any problems with it as that is true.

I believe they considered that.

What do you bench, squat, deadlift, clean & jerk, and snatch? What is your BF%? This information would tell me much more about you "physically" than your BMI.

Well, first of all, the study in question is about overall trends. Such generalizations don't account for all individual situations. Consequently, this whole line of dicsussion is not relevant, nor am I going to start talking about the degree of my strength or whatever. I'm more than strong enough.

yet BMI indicates I am an unhealthy slob.

No, it indicates you are overweight relative to norms. Being overweight and being strong are not mutually exclusive. Usually, one's cardiovascular conditioning is more directly related to relative mass, and even then some people are just big boned type of people. But in general, specific variations wash out, and then one can find overall relationships, as covered in the study these folks did.

According to BMI Ian Thorpe (sure wish I swim like him) is "overweight" at a BMI of 27.4! ... give me a break

Remind me again of what percentage of the populace are professional athletes.

These are tools to use, not universal arbiters of some hard truth. Again, the larger the population base, the more relevant the measuring tool is. Unless of course the thesis is that Americans are just all big boned, not big tubs of lard.

The only factors they considered, as represented by the summary, would be weight of cargo and poor maintenance. I'd like to see the entire report to see if they also took into account the weight of the vehicles, the horsepower of the vehicles (per ton weight and absolute), emissions equipment, addition of accessories (a/c and p/s were not common in the 60s), efficiency changes of the vehicle (consumption per ton weight), etc.

Add to that list driving distance and congestion as well.

"These are tools to use, not universal arbiters of some hard truth. Again, the larger the population base, the more relevant the measuring tool is."

I'd say any tool that is as limited and faulty as BMI needs to be thrown out and replaced with a better tool. Its use in this report makes me wonder about the accuracy of the rest of its results.

The only factors they considered, as represented by the summary, would be weight of cargo and poor maintenance.

Read again. It says those are examples of things they factored out.

Again, you are assuming this paper to be much more simplistic than it almost certainly is. Not a good assumption to make.

...and those are the only examples they cite and thus why I mentioned "I'd like to see the entire report to see if they took into account..."

I want to know exactly what they took into account for their mathematical model. On the surface this seems very *sensational* without very much substance. I want to know if it has any *meat* to it when I get a chance to digest the actual report.

..and those are the only examples they cite and thus why I mentioned "I'd like to see the entire report to see if they took into account..."

Great. Then stop speculating, as I asked you to do far upthread. You're leaping to all sorts of conclusions without even knowing what they said.

I want to know exactly what they took into account for their mathematical model.

You'll have to wait for that, won't you? Until then, you're just speculating -- in a way that presumes they're all flaming idiots instead of PhDs.

On the surface this seems very *sensational* without very much substance. I want to know if it has any *meat* to it when I get a chance to digest the actual report.

And your qualifications for judging whether it has meat are...?

Get back to us once you have a chance to read it. Until then, any speculation about details is superfluous.

"The conclusions, Jacobson said, should be considered conservative because they do not consider many indirect consequences of obesity nor the increase in the number of vehicle miles linked to more people living in the United States and owning cars."

So, increase in vehicle miles is not considered. Does that mean the data is "corrected" for vehicle mile differences or does that mean it is not taken into account and thus the increase in fuel consumption could be related to people driving more miles. That is a question I have. How does the number of people and the vehicle miles driven make the obesity driven fuel consumption numbers seem conservative? Do obese people have more kids and drive more miles?

Why not track a statistical sample. Find out their average weight every year and their fuel usage. This, would seem to me, to be more useful in the context of this research.

Fleischman and Pons have PhDs...they were not idiots but they let a goal overshadow the basics of the research rather than let the research achieve a goal.

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