> are people in Colorado leading such hugely different lives from the rest of the nation?

Yes, absolutely. I've spent time in very obese locations in the midwest, and spent time living in Colorado and have relatives there.

The lifestyle differences are exceedingly stark. Drastic even. It's clowned on for the hippie/health conspiracy nutjobs meme for a reason. You immediately realize why people look different.

> And are people in Colorado leading lifestyles more similar to those in California than those in Kentucky?

Yup. Again, this is obvious simply from spending time in both locations. You will find places in CA that are nearly as obese as many places in KY, and find that the lifestyles look quite similar between the two. Louisville lifestyle is quite similar to Bakersfield for example and the obesity rate just so happens to coincide with that observation.

I don't know enough about Tonga vs. France to comment, but I imagine if you spent a few months living within the populations of both and living a typical lifestyle/eating a typical diet you'd likely find immediately obvious differences. In this case, genetics is also a very plausible front-line explanation - where in western countries it simply is not due to similar demographics changing so drastically over a generation or two while removing the immigration confounder.

> To me, the much more plausible explanation is that there is some aspect of modern life

Yeah, it's the diet combined with a relatively fast switch to sedentary lifestyles. Mostly the diet and food environment. Participation in adult casual sporting leagues and other outdoor activities is right behind it. Changes in the average activity levels while at work. Just 12,000 steps a day makes a drastic difference in weight for many people.

Technology plays a major role - screen time went from minutes a day to double-digit hours for the majority of the population. Hard to be active while staring at a screen of any sort.

Like I said - I'm also open to some environmental variable not explained by much simpler facts like the food environment, but I think that's exceedingly less likely than what is smack dab obviously right in front of our faces that for some reason we ignore in pursuit of near-conspiracy level stuff. The obvious thing usually ends up being true, and I see no reason in this case to believe otherwise.

Again though - exceptions abound. Humans are complex creatures. They average out quite well though at population scale.