The agricultural complex has given us rampant obesity,
That's one of the major causes. The other major cause has to do with the de-industrialization of major sectors in Western economies. What I mean by that is that the majority of workers have jobs that involve very little to no physical activity.
I've got a great example!...
When I was 16 I moved in with my aunt (father's sister) and uncle who became my legal guardians, mainly so that I could attend the high school in their town (my aunt helped raise me and thought a change might do me good...bless her). They were both unusually slim even for the 80's. He had acquired a small belly, man loved his beer but mostly blamed his evolving job.
He was a long-time dispatcher at a concrete company. He sat in an elevated room and manually calculated the proper mixtures and loads for each job/truck, then had to manually push and pull levers to load the trucks. What I remember was that he was always on the move in that little room.
By the time he retired he was in the same room sitting behind a screen, keyboard and mouse, entering numbers. The loading process had become fully automated, he never needed to leave his chair.
You can't stop progress nor would you want to, you just have to recognize that you may not be as active with everyday tasks as you once were, which is why we have gyms these days.