[i_am_proteus]

>Sure, but that happened well before WWII, while the obesity epidemic started sometime around 1970-1980

This is not correct. Mass-scale industrialization of US farms didn't start happening until the 1930s. Remember that it was the internal-combustion engine (not the steam engine) that permitted the use of tractors and other machinery to supplant human and animal labor.

Now consider that it takes time for humans to become obese. The children raised during the beginning of the massive agricultural surplus were precisely the ones who were fueling the start of the epidemic in the 1970s.