It seems like AN males used to have lower death rates from IVD than white males in the US, but as those rates dropped for white males they stayed the same for AN males.[1] This study is from a period where the AN male population over ~40 was still primarily eating a traditional diet. SO it seems like the traditional diet was better than mainstream diets from the 80s and 90s, but probably worse than a good diet today if I may extrapolate a bit.
[1] https://www.tandfonline.com/doi/abs/10.3402/ijch.v62i4.17579