I think the first I learned of transfats was an article in Gourmet magazine.
My aunt lived on a farm in Mississippi her whole life … I watched her make butter from milk from her cows. Later in life, no more cows, she bought margarine from the local store. I thought: how could she eat margarine after eating that delicious butter all her life.
I don’t remember any connection with healthiness! I don’t recall seeing butter in any kitchens (outer boroughs NYC sixties and seventies) until I moved away and was an adult.