Shifting Waistline Syndrome

August 5, 2011

in Science

by Rob Schick

“My name is Johnny Hake. I’m thirty-six years old, stand five feet eleven in my socks, weigh one hundred and forty-two pounds stripped…”

From “The Housebreaker of Shady Hill,” a short story written by John Cheever in 1958.

In 1995, fisheries scientist Dr. Daniel Pauly, of the University of British Columbia, published a landmark paper in Ecology’s top journal entitled “Anecdotes and the shifting baseline syndrome in fisheries.”

The premise of the paper is that a scientist’s understanding of the decline of fisheries stocks worldwide is tied to when he or she started their career. For me, the key line in the article is:

“Each generation of fisheries scientists accepts as a baseline the stock size and species composition that occurred at the beginning of their careers, and uses this to evaluate changes. When the next generation starts its career, the stocks have further declined, but it is the stocks at that time that serve as a new baseline.  The result obviously is a gradual shift of the baseline…”

Dr. Jeremy Jackson, another prominent marine ecologist, characterized this well in a paper in 2007. (Tip of the hat to a nice article about this by Christine Ward-Paige.) While discussing what is “natural” for the coral reefs in the Carribean, Jackson says:

“The problem is that everyone, scientists included, believes that the way things were when they first saw them is natural.”

I propose that what we think of as “natural” or normal levels of obesity in this country is changing with each generation. When I read the John Cheever story quoted above, the weight caught my eye, as it seemed very light to me. Sure enough, the Body Mass Index (BMI) for the fictional narrator in Cheever’s story, published in 1958, is 19.8. According to the CDC, the average adult male in the US today has a BMI of 26.6 (26.5 for women).

What does a person with a BMI of 19.8 look like? Well, most people would look at Andy Schleck, professional cyclist and three-time runner-up at the Tour de France, and think he’s awfully thin. Certainly much thinner than average.

Andy Schleck

Photo credit: Andy Schleck Official Website

Schleck’s BMI? 19.7. I’m sure if I stood next to Schleck, he’d seem very thin in comparison. In contrast, if Schleck stood next to Cheever’s narrator, they’d look the same (well, save for the fancy biking outfit!).

Two recent news items caught my eye and reminded me of the parallels between the obesity epidemic that plagues America, and the idea of shifting baselines proposed by Pauly.

First, in March, the Federal Transit Administration published a proposed change to the assumptions for average weight in passengers on public buses. Specifically, they proposed changing the assumed average weight from 150 to 175 lbs.

They proposed the change because Americans are getting heavier, which means public buses aren’t built to accommodate the heavier load and, as such, are less safe as passenger vehicles.

Why should we care about this? Well, let’s run through a little thought experiment and imagine a bus got into an accident. If you remember your college physics (I don’t remember much; I got a C in mechanics – from Hans Dehmelt no less.) you’ll recall that force = mass * acceleration. So the more mass in the bus, the more force that might result in an accident.

Say there are 55 passengers on a bus. At 150 lbs each, that translates into 8,250 lbs. total weight, which is what the current safety regulations account for. At 175 lbs, 55 passengers equals 9,625 lbs, or a difference of 1,375 lbs. If we use the actual average weight of men today (~197 lbs.), the mass in the bus is even greater, and you can see where I’m going with this. If you are in a Honda Civic and you get hit by another Honda Civic, you’re better off than if you get hit by a Hummer.

If you don’t regularly read the Federal Register, the proposed weight change was widely covered. An interesting section of an article from USA Today highlighted the theme of Pauly’s article:

“Current federal guidelines on average passenger weight are based on surveys in 1960-62 of what Americans weighed then. Today, the Centers for Disease Control and Prevention says, the average weight is 194.7 pounds for men 20 and older and 164.7 pounds for women in that age range.”

So what’s happened? Our baseline has shifted – and so have our waistlines. What was a normal weight in the 1960’s is no longer normal – it’s very thin by today’s standards. To accommodate this increase, manufacturers either have to reinforce the existing buses, or remove seats to allow for the additional passenger weight.

The second news item, an article in the LA Times, covered the release earlier this month of a new report on obesity in America, and noted we’re changing our baseline about what defines obesity.

In 1991, the state of Colorado had one of the lowest obesity rates in the country. While this is still true in 2009, the rate of obesity has increased. In fact it has increased so much that if you put Colorado’s rate from 2009 back in 1991, it would be the highest in the whole country.

Again, the baseline has shifted. What appeared normal in Colorado in 1991 would be lean by today’s standards.

Below is a map that shows the percentage of people who are obese in each state over each of 4 years. Obese is categorized as a BMI over 30. The data are from the CDC.

Obesity Maps

I don’t intend this piece as an anti-fat polemic, what I intend is that we be aware of what baseline we use when we look at future obesity trends. We all know we should be leaner, as we are bombarded with that message in today’s popular press.

Instead of comparing our weight to our generation or our parents’ generation, we might want to shift our baseline to our grandparents’ generation. Instead of merely building bigger buses, we might want our government to urge the industrial food complex to make it easier and more affordable to eat whole foods instead of subsidizing hyper-palatable and hyper-caloric junk food.

A few more resources for you to read and use:

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