I am sure that in the past, good or bad food was more about conservation and food borne diseases than it was about nutrition. At least, that's the attitude that would make the most sense. That would explain sugar good / fish bad. There is probably a political aspect too, local food is seen as better than the rival neighbor food.

The modern, first world attitude must be very unusual towards history. We basically solved conservation and food born diseases are now uncommon and mostly treatable, and we have an abundance of anything, so nutrition is the only thing that remains when discussing healthy food.

What didn't change is the made up theories surrounding food. Despite all our science, we still have a lot of these today, in some for or another.