First of all, I agree that gaining weight for individuals is a globalized issue (or at least, first world issue).
And I've never seen so many "gigantic" people as I have in the USA, except maybe in a Sumo game (please, a little bit of humor
).
Anyway, I've also never been to the Samoa islands
I can't talk for all of Europe ( although I also know quite well the culture of Belgium and Italy, having lived on the very near border of both) so I'll stik to my country.
There is a factor really pregnant here, that (unless I missed it) hasn't been mentionned at all in the whole thread.
We still and continually do what Americans call "
fat shaming". It will start as soon as you have 3/5 pounds too much, even as a kid or a growing teenager Not in a mean way, more in a joking way, but you can't ignore the real meaning. It starts with your parents but even a total stranger may stop you in the street and tell you to lay that croissant off.
While I understand that it makes/ccan make for a weird relationship for your body, it also means that there is a "standard" that is not to be lost and having only 5 pounds to lose is WAY EASIER than 150. You don't even have to make an effort actually, just be careful for a few weeks.
I also think, as in Italy, we eat more seasonnally, still cook much more often at home, fresher produce and a lot of the crap that is sold in many places is simply forbidden here (the crap that is actually sold IS OBLIGED BY LAW to tell very clearly on their label what it contains).
Another cliche : nobody has cars so we walk everywhere.
Not true. Almost everyone has a car (except single people in big cities), we city people just tend to use them less because there's always a baker or butcher not far and public transportation is quite efficient so we walk without noticing or use one of the free-renting bike more and more cities are offering as a system. Cars are for the week-ends.
I would tend to think that city people walk much more as it's more convenient than driving but cook less as they have bigger hours to fill (commutes, etc). Country people walk less, they need their car for errands, but they tend to have more time in the day to keep a vegetable garden for example and cook both meals of the day rather than eat a quick sandwich at lunch.
It balances that way between city and small towns/country people.
But really, the fat shaming is also a if not THE major factor. French women are supposedly amongst the thinnest in Europe but would you believe more than 3/4 of them think they could lose a few?
Is that a good thing or not, I don't know, it's so ingrained in my system. All I can say is it never made me ill at ease, or just enough to rectify my ways when subjected to it. But if not the truth, at least it's my truth.
I think Italian people have a culture that resembles it so maybe someone would like to chime in?
Also children canteens are not at all the same. Children eat for 40 minutes with no choice in what they get (except when you're an older teenager and then it's only a choice between two courses equally verified by a dietetician), "lunch ladies" showing them how to use a fork and knife from the age of 3, taking their time ad only water served. Salad is always served, some kind of meat, starch and vegetables, and then either cheese (my 3 years old niece loves brie and roquefort) or dessert, unless it's a yogourt and fruit.
Not to give lessons because I can't ignore that obesity is also growing here but I think there are more reasons to French don't get fat than a nationality of origin, it's cultural.
I also believe we're all to face this (monsanto and all) worsening of our food in the next decades. Let's learn from each other rather than oppose rivalries.
Have fun!
ETA : as others have mentionned, these stats aren't really accurate as they don't distinct between the levels of obesity.