Wednesday, November 01, 2006

Overweight? Don't Blame Suburbia

I've had a bone to pick for a long time with folks who feel that our rapidly growing waistlines are attributable to a lack of exercise.

I have an even bigger bone to pick with those who say our lack of exercise is due to growing rates of urban sprawl.

Fact is, the numbers for me just don't add up.

It's a very unfair thing - the number of calories burned through exercise isn't anything to write home about. Therefore I struggle with the notion that weight in society is going up due to a lack of exercise let alone a lack of simply being able to walk to your corner store.

Many studies have reported that the less walkable neighbourhoods of suburbia contribute to obesity and they conclude that by reporting that the percentage of those who are overweight or obese are higher in areas of urban sprawl.

The problem with that argument is that we really don't know if it's cause or effect.

That is perhaps, until now.

In a paper that came out of my alma matter, Lawrence Frank at the University of Toronto has published a very nice piece of research. In a paper entitled, Fat City: Questioning the Relationship Between Urban Sprawl and Obesity he does just that (question the relationship).

Basically what Dr. Frank hypothesized is that perhaps weight in fact impacts on choice of neighourhood, rather than neighbourhood impacting on weight.

He and his team took data from the very unsexily named Confidential Geocode Data of the National Longitudinal Survey of Youth 1979. They followed 6,000 individuals during a 6 year study period. They tracked these individuals' residential addresses and weights over time. What they were looking for was whether or not individuals gained weight when they moved to a more sprawling neighbourhood or lost weight when they moved to a less sprawling one.

To summarize a fairly complicated paper is Dr. Frank's conclusion,

"Overall we find no evidence that neighbourhood characteristics have any causal effect on weight"
I also agree wholeheartedly with their statement,
"It follows immediately from our results that recent calls to redesign cities in order to combat the rise in obesity are misguided."
That's not to say there's no value in improving the "walkability" of neighbourhoods - I'm all for that, but I'm for it to encourage fitness, a very important determinant of health. What it won't do is affect weight.

The math's just not there.