Diet definitely has a bigger impact than exercise, but isn't there still a correlation between more urban areas and lower obesity even when controlling for poverty?
There may be other factors to urban, non-car-based living besides the extra physical activity that encourages lower weight. It's maybe as simple as without a car you can't go to Costco and stock up on huge sacks of unhealthy foods in one go -- beats me, I'd be interested to learn more.
On my phone so I can't find the right metastudy but yes, there is an inverse correlation between urban lifestyles and obesity rates but it's a tenuous one. In cities like Atlanta, St. Louis, Montgomery, and San Antonio the difference in obesity rates from rural and suburban areas in the same state is almost nonexistent but Houston, Los Angeles, San Francisco, and New York see much lower rates in obesity. (within city limits, their metropolitan areas are a while different animal).
I have a feeling that it's mostly due to a hybrid peer pressure/economic effect. When you're in a group of friends and the majority want to go to a healthier restaurant or everyone in your neighborhood goes to the local mom and pop grocery store instead of Safeway, it becomes a self reinforcing pressure to eat healthy. More healthy restaurants will open and more small grocery stores will be built to serve individual neighborhoods while market share is slowly taken from unhealthy restaurants and chain groceries. Eventually, a significant portion of people who would otherwise have trouble controlling their weight stick with the healthier diet out of inertia or convenience.
I also saw a study (although not a very conclusive one) that suggested that discrimination could play a part. A higher cost of living in cities means that a lot more jobs that can support the lifestyle have a physical appearance component to them. Salespeople in high end boutiques, consultants, etc are economically more viable in denser areas and if clients or employers discriminate based on looks, there will be fewer job opportunities for the obese, making it harder for them to live in urban areas.
Do you know if there's a study that breaks this down by population density instead? My intuition (having lived for 6 years without a car in Atlanta) is that obesity levels aren't going to be significantly different in a sprawling, low-density city like Atlanta, where everyone drives, but in a dense, walkable, and public-transit friendly city like NYC you will see a difference.
Not off the top of my head but there are plenty of such studies. That still wouldn't give a clear picture because Los Angeles is also a low density car centric city but because it's in California, healthy eating is culturally more prevalent and fresh food is easier to come by.
All the factors matter, and obesity definitely has a social component.
The jobs not only have a physical appearance component, the performance expectations and constant competition may mean you need more endurance. I'm not fat, and I'm not ripped, but I sure as hell feel a major performance boost in my own work when I eating healthy and exercising daily vs when (years ago) I was sitting inside all day drinking soda. I can't imagine how I would feel or perform if I had kept that up post-30.
Chain restaurants share commonality with big box retail. In a major city taking a client to Applebees much less Mcdonalds isn't going to cut it. In some cases rent may be too high to even support their business model, replaced instead by small shops and food trucks and larger restaurants at higher price points.
If the car was less important, the parking lot didn't matter, and people walked, would everything collapse in to more centralized walking cores? If so, would they serve anything healthy, or are the big cities an outlier because of the wealth and performance pressure?
There may be other factors to urban, non-car-based living besides the extra physical activity that encourages lower weight. It's maybe as simple as without a car you can't go to Costco and stock up on huge sacks of unhealthy foods in one go -- beats me, I'd be interested to learn more.