Since you mention Ancel Keys, and the fallout from his purely associative studies, I'd like to point you to an excellent and very recent post on dietary fat (https://medium.com/in-fitness-and-in-health/our-understanding-of-dietary-fats-is-evolving-are-you-up-to-date-73eb53ceecac) authored by Dr. BenJones. There is not much left of those cholesterol and fat myths that plagued our diet in the 70s-90s.