A casual look at where people live the oldest, what they eat, and what's recommended tell you all you need to know about food recommendations then and now.

It's a field where actual long term controlled experiments are impossible, confounding variables are everywhere, and multiple lobbies have vested interests in the outcomes.

I take everything with a grain of salt apart from studies of harm when sources are credible and numerous and even then, I'm not fully confident.

The only current advice I follow is avoiding industrially processed food. That sounds like a sound one as this kind of food is basically terra incognita. It's just applying the precaution principle.