My theory is fairly broad and vague, but your comment has taken those two things to an extreme.

I'm just pointing out that your theory is trivially disproven.

An excess of comfort is probably still bad, but I doubt it's the main cause of obesity.

It all hinges on how we define comfort. A comfy villager 500 years ago, with fruits and meat nearby was probably never really hungry, but, I'd argue:

- never the amount of processed calories at hand - had to consume these calories on a regular basis.. no vehicles, no powered tools except the occasional mill, most things required walking of lifting

Obesity in the US didn’t really start taking off until the 1970s. There are plenty of people still alive from the before times. I believe that studies have been done, and people aren’t generally less active now than they were then.

But the generations prior didn't necessarily have a car. And a lot of jobs were manual labour.

I know that since I dropped using a car I'm living very different days. Less fat, better cardio, more calm.