> Americans ate more calories in 1909 than in 1960
They also did A LOT more manual labor back then. Heavy construction projects (roads, dams etc.) were still performed by thousands of people literally swinging a pick-axe 10 hours a day, slowly chipping away at the hill that stood in the way. That must have required couple thousand of extra kcal per day. Meanwhile, in 1960, a lot of most energy-consuming work was already performed by machines.
Some of them just worked at desks. Actually quite a few. And they were thin too. You can find pictures of the typical city office-worker if you hunt through the Library of Congress archives.
They also did A LOT more manual labor back then. Heavy construction projects (roads, dams etc.) were still performed by thousands of people literally swinging a pick-axe 10 hours a day, slowly chipping away at the hill that stood in the way. That must have required couple thousand of extra kcal per day. Meanwhile, in 1960, a lot of most energy-consuming work was already performed by machines.