Sci rather wishes this study were done in mice, if only so she could write "the city mouse and the country mouse" in her title. But it was done in humans, which was really probably a good thing.
This post has some background. Sci was sitting around with her lab one day, shootin' the breeze like you do when it's Friday and science has you cross-eyed, and we were talking about going to meetings in exotic locales. We were talking about one especially large city, and one person in the group said "you know, what's amazing about cities is how THIN everyone is". And everyone in the group nodded sagely and said it was always shocking to go to large cities and realize how skinny everyone was.
But, being a scientist, Sci wondered...is this really true? Are people thinner in the city and thicker in the country, and if so, why? Is it just our perception, due to some cities featured on TV being full of starving artists and lots of plastic surgery? Is it universal? Is it just among the upper class? What about the urban poor? And is it due to all the walking, or is it just because of increased populations of starving artists?
And that's not all. Sci just hopped up and moved to a new, Very Large City, and for the first week or so, my feet DEFINITELY noticed the walking increase. The blisters on my feet especially. Apparently every other female on the planet knew about those gel insoles to help you wear pretty shoes, but Sci apparently flunked that part of her "how to be a girl" exam.
So relationships between physical activity and obesity? Sci shot off an email to Travis of Obesity Panacea. Travis sent her a paper citation. Let's do this.
Frank et al. "Obesity relationships with community design, physical activity, and time spent in cars" American Journal of Preventative Medicine, 2004.
(Put on your walking shoes! Sci hates those obligatory pictures of obese people next to pictures of people who are obviously models. This one is better.)
The hypothesis behind this study was simple. Are people more physically active, and are they less obese, when they live in environments which promote physical activity. This isn't just living next to a gym or a park. Rather, it's living in a place that facilitates activity. This doesn't have to be extreme, it's as simple as being able to walk places.
You might say, being able to walk places IS simple! Not always. In the case of many rural and suburban neighborhoods, walking is something you do specifically for leisure or exercise. You don't walk TO places, because you CAN'T. Every place you want to get to is a good 15 minute drive. In contrast, in urban settings it's often easy to walk places, things are nearby, and there are often sidewalks. But not all urban settings are easy to walk in, due to problems like crime and traffic safety.
So for this study, the authors surveyed over TEN THOUSAND people living in and around Atlanta, Georgia. And they looked for some interesting things. While they looked at age, ethnicity, income, and education, they ALSO looked at the number of hours spent in a car, the distance walked, and the LAND USE of the places the people lived. By land use, they checked for what the land was used for (residential vs otherwise), the density of people living there, and the connectivity of the streets. Were there lots of sidewalks? How easy was it to walk around?
And then they put it all together and churned out some correlations.
They found correlations between age and obesity (if you're older you're more likely to be obese), and car time and obesity (the more time you spend in a car, the more likely you are to be obese). They also found negative correlations between education and income and obesity (the more education and money you have, the less likely you are to be obese), and a nice negative correlation between walking distance and obesity (the more you walk, the less likely you are to be obese).
And then they put it all together and mixed it up with some land use data.
What you can see above (if you can get past the cheesy, somewhat difficult background to the figure, yeesh people, that doesn't help!) is the subjects, divided by ethnicity and sex, and curves representing land use. The "mixed use" term refers to when land is devoted to more than one thing (residential and commercial as opposed to purely residential or commercial or industrial). So on the left side of the graph you can see the average mixed land use of 0 (stuff is either residential or commercial, not both, this is relatively average), and as you go rightward on the x axis, you see the land use get more mixed, as in a more urban setting.
The curves are plotted as probability of obesity, and plotted over the land use, and you can see that residents of areas with low mix land usage have a higher probability of obesity than residents of high mix land usage.
Well, now we know land use, but does that necessarily mean that people living in high land mix settings are walking more?
This figure certainly shows that walking, across all demographics, reduces the probability of obesity. Sci would LOVE to see this laid over some land use data so you could see whether the people in the high mix land use areas were walking more and were also less likely to be obese. There was a significant effect of this, but they didn't graph it.
And finally, the rough one:
This figure shoes the relationship between probability of obesity and the number of minutes spent in a car per day. First of all, some of these people were spending 8 hours a day in a car (I really hope they were taxi or bus drivers, but that doesn't make it much better). But regardless, there was an increase in the probability of obesity associated with increased time spent in the car.
So, to recap:
1) The more the land use is mixed where you are, the less of a probability you have of being obese. This is presumably related to walking more, but the correlation was only effective for African-American females.
2) The more you walk, the less probability you have of being obese.
3) The more time you spend in a car, the MORE probability you have of being obese.
Sounds pretty simple, don't it? But this isn't the easiest thing. Many people HAVE to drive to work, and often do not have enough leisure time outside of it to make up the car time with other physical activity. In addition, many people will walk more when they have somewhere to go, and suburban residential neighborhoods don't really go in for that kind of thing. But it DOES provide some interesting data for people looking to plan new residential communities. If you make things more walkable (especially work and necessities), maybe people will walk more, and maybe that will translate to smaller probabilities of obesity and improvements in health. Maybe those people planning those overly picturesque walkable communities are on to something.
(Sci wonders if, when all communities are walkable, everything will magically appear in soft watercolor. We have sepia-toned memories, behold the watercolor future!).
FRANK, L. (2004). Obesity relationships with community design, physical activity, and time spent in cars American Journal of Preventive Medicine, 27 (2), 87-96 DOI: 10.1016/j.amepre.2004.04.011