I would hypothesize that whether or not one has a job or hobby that makes you sit still all day is a much more relevant determinant than which country one is from.
Japan is full of those kinds of jobs, yet their obesity rate is only 3.6%, compared to america's 32%.
Diet is more important than exercise when it comes to weightloss because the majority of our metabolism is resting metabolism. Even when someone exercises like hell, it only makes a small dent in their overall metabolism. That's why body builders have to starve themselves to achieve their picturesque forms.
Usually when we see regional differences in weight gain, it's due to differences in food regulation and culture. Stuff like the maximum amount of
sugar or salt that can be put in certain types of food (america's standards are the laxest), maximum
serving size (Have you heard of 7 eleven's
Big gulp? Good luck finding that outside of the States), as well as how freely companies can
advertise junk food.Depending on the country you live in, obesity can either be something you have to actively put in effort to avoid, or something that is so hard to achieve that you have to basically be trying to get fat.
Here is a
video that nicely outlines all of the forces that make it hard to get fat in japan as an example.
It's frankly amazing how much you can learn by looking at laws and customs of cultures outside if your own. Chile's
food labeling reforms are a beautiful example of an effective weight-loss policy that can be adopted by other countries. Obesity is a big burden on a country's healthcare system, so it's important to find effective ways to tackle it.