I think part of it was their work ethic. Old college roommates grandfather was throwing 50 lb hay bales in his 70’s. He was kicking my @$$ and I was in good shape.
My FIL lived to be 87 and ate everything listed including real butter.
I am 88 and have never watched my diet....always ate whatever I wanted....never a weight problem either. Good genes,I guess.
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They are all that food cooked with good butter and bacon fat. My mom used to have a Folgers coffee can in the fridge full of gross looking bacon fat. Scoop some out and cook it up. They eat and go work all day. I think some was hard work and also the food wasn’t filled with preservatives and pesticides and other harmful chemicals.