Which contains all my thoughts about dietary fat recommendations and the lipid hypothesis, without too many distracting details.
I also want to supply a link to a most enjoyable book, Bertha M. Wood's "Foods of the Foreign-born in Relation to Health" from 1922.
https://archive.org/details/cu31924003579756
I think this is the first record of "dietary transitions", adverse changes to the traditional diets of migrants in a new land. It was written at the height of U.S. xenophobia (in the immediate aftermath of the Great War and the Bolshevik revolution) and can also be seen as a response to prejudice. Though the Hungarian child's diet below might not have helped much.
In 1922, diabetics were treated by restricting starch, especially from grains and legumes; this was replaced with non-starchy vegetables. Fat was not generally restricted (though this is said to be necessary in some cases, perhaps because sugar doesn't seem to have been reduced).
I learnt about Bertha M. Wood's book from The Old Foodie blog.