Americans eat 25% more calories since 1961. It's that plain and simple, no need for monsters hiding under the food.
As a proxy, 47.7% of children walked or biked to school in 1969, and that fell to 12.7% by 2009. https://archive.cdc.gov/#/details?url=https://www.cdc.gov/po...
This mirrors general commuting changes in the Census.