"The China Study" was very famous but also pretty notorious for selling the idea that illnesses like Cancer exploded in China after their recent economic boom in the 90s-2000s, pointing to the rise in meat consumption as the source. That's about as observational/macro of a propositon as it gets. Especially with all the other stuff like mass urbanization.

This review explains both the book and the science better than I could

https://www.redpenreviews.org/reviews/the-china-study-the-mo...