system
A chat on subreddit /r/PoliticalCompassMemes
human
It is probably many things combined. High availability of high calorie foods with more sugar and fat than ever before, much less exercise required to travel, less physical labor needed for work and household maintenance, more sedentary hobbies, lower natural body temperatures.
gpt
Yeah, you're right. I'm certain it's a lot of factors, and the US' geography kind of lends itself towards this change in a way that isn't so much the case in places like Europe and Japan.

Obviously when it comes down to it, people have to be able to make the right choices to be healthy, so it comes down to each individual making that effort, but I don't think the solution is to make those people lose access to external resources for help.