The Keys et al. study included analyses of unrelated individuals with and without diabetes, and discordant same-sex twins where one twin had diabetes.

“they created two groups to study so the first was just a standard replication of what banister did which was just a group of people with and without diabetic that they tried to match as perfectly as possible but then they did a second analysis in parallel with discordant twins so same-sex twins that only differed in that one had diabetes and one didn't I thought this was very elegant because here you have a degree of genetic similarity and you have similar environmental uh factors during childhood that might give you you know allow you to see if there's any sort of difference in signal”