alt Hacker NewsI'm about to say something that is easy to dismiss as bullshit, so feel free to, but you're right, people were healthier in terms of weight in the 60s, and right around that is when we changed dietary guidance to be carb-focused, low fat, etc. Since then, obesity has skyrocketed. The book Obesity Code covers this.
As sibling comments have pointed out, 3800 is availability, not consumption, so it's not an indicator of how much people do eat, just how much they could eat.
You can see it if you watch any US documentary filmed before the late 70s that shows ordinary people in the street. They're much fitter, and exercise for weight loss wasn't really a thing yet; people didn't jog. That's not far enough back that everyone was a farmer or laborer; there were plenty of fairly sedentary office workers. They also weren't starving; it was a prosperous time. They were generally eating meat-and-potatoes diets with plenty of animals fats (I have a 1960s barbeque cookbook that tells you to put a pat of butter on pretty much everything). And obesity wasn't a problem.
And since we started letting the government tell us how to eat healthy, not only has obesity skyrocketed, but so have diseases connected with it.