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…
Almost everything that isn't a single ingredient whole plant or animal food contains industrially processed oil or sweetener/starch.
Still worth doing imho but I understand why it's not easy for most people.