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Green Wheels

Green Wheels: Can obesity affect fuel efficiency?

Published October 26, 2012

Carmakers are struggling to meet tougher fuel economy standards.

They’re working hard to squeeze more energy out of engines, employ lightweight materials and tweak designs to cut wind resistance.

Could this effort be undone because I, like most Canadians, enjoy doughnuts and fries?

More: Lose weight to save gas? Not so fast

Allstate, the insurance giant, claims that’s the case. At least, it’s the gist of an infographic posted under the company’s name.

It’s based on American figures, but we do tend to follow their lead.

The main message: The average American’s weight is at a record high, and they’re burning more gas to haul that poundage around in their cars.

More than one-third of Americas are obese. Last year, their average weight hit 160 pounds for women, and 196 for men.

Just two decades ago, no U.S. state reported an obesity rate of more than 19 per cent. Now, they’re all above that figure.

“High gas prices and increased pressure from federal regulators are pushing car manufacturers to create lighter, more fuel-efficient vehicles,” the infographic states. “However, the growing … obesity adds unexpected weight to vehicles, making it difficult for consumers to realize fuel-efficiency gains.”

Every 100 pounds of excess passenger burden cuts fuel efficiency by two per cent. Every pound in total passenger weight adds about 170 million litres to the United States’ annual gasoline consumption

That’s just 0.7 per cent of the total, but still significant.

Perusing these numbers compelled me to sit down with a coffee and chocolate croissant to digest this news. And the blast of caffeine and sugar gave me enough energy to dig deeper.

It turns out that the blog — just like a good Boston cream — is mushy and gooey inside.

Most of the figures come from a 2010 Consumer Reports item, which, in turn, cited “a detailed study published in 2006 at Entrepreneur.com.” Consumers Reports helpfully added a feature on the five top cars for fatties.

Although the results of the 2006 study are widely quoted, I haven’t yet found any details of how they were reached.

But Consumer Reports also refers to a 2009 study by non-profit group Resources for the Future that blames most of the higher fuel consumption on the fact obese people buy bigger vehicles, which consume more fuel.

It’s a simple statistical match: As the obesity rate increases so do purchases of vans, SUVs, and pickup trucks.

But just because numbers rise and fall with each other doesn’t prove cause and effect. And the study does observe: “Other factors helped drive this market change, such as those crude, commercial-type vehicles becoming more refined and better tailored to commuter duties.” Not to mention that, inspired by their hefty profit margins, carmakers promote them heavily. And drivers, big and small, simply like them.

That’s not in the infographic.

This reminds me of a study three years ago by a prestigious British research institute that concluded — this was a newspaper headline — “Fatties cause global warming.”

It claimed obese people gobble energy because they eat more and walk less; with the additional driving in big, heavy gas-guzzlers.

Those assumptions failed even mild scrutiny. As do some of the infographic’s numbers.

Of course, the more weight in a vehicle the more gas it will burn, but I wonder why Allstate felt compelled to publish stuff largely based on a basic statistical fallacy.

A spokesperson insists it’s not an attempt to alter public policy or individual behaviour. “There’s no call for change other than to say, ‘hey, you may not be aware of this … this is something that could apply to you.’”

That’s fine and useful. And there are plenty of reasons to avoid obesity.

But this effort left me feeling manipulated, and, contrarian that I am, that drove me to a second chocolate croissant.

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