The giant portions thing is a cultural left over in a lot of ways, food used to be cooked in a far more communal method and often combined supper and lunch then a snack later at night. For example apparently my 2x great grandfather ensured a small feast for him, my great grandfather, his wife (remarried technically not my ancestor), and all the temp workers during harvest. That's not even getting into things like potlucks.

As for sugar I blame the post war period, arguably the amount of sugar in shit has been decreasing slowly since the 90s but it's a slow generational thing.