We've always known that our government's diet advice was variable. We learn in retrospect of this problem's root cause in a battle waged in the '70s.
personal correspondence
The research which led to the low fat diet was centered around the search for the causes of heart disease.
The science was around in the 1970's when the low fat diet was proposed as opposed to low sugar (John Yudkin). Just the wrong person (Ancel Keys) who proposed low fat won.
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John Yudkin vs. Ancel Keys. search 
A bumper sticker popular among Hoosiers of the era read, "Vote Republican or Lose Your Butz". wikipedia
I recently had the opportunity to dine with Deans from the Illinois Institute of Technology. My wife who traveled back to the midwest with me was a little concerned when we were seated with a woman leading research of public health in aging. When the subject did come up I glanced briefly at the walls, acknowledging where I happened to be, and said, "corn syrup". Nothing more to say.