re: Medieval farmers ate 7000-9000 calories a dsy

No idea what the calories per day were, but I do know it took a huge amount of food to supply the crews building the transcontinental railroad. Which was all manual labor at that time. No steam shovels or track laying machines.

eta-Hell, I worked a summer on a section crew for a shortline railroad back in the 80s and we did everything by hand and I at like a horse and never gained weight. Got pretty damn powerful though.

A lot of those "skinny" farmers are a lot stronger than they look for the same reason.