As a complete non-expert, as far as I can tell, the only true agreement out there is that certain very specific substances are bad for you if you consume them too often. That's tobacco, alcohol, painkillers...and that's about it for consensus ones, with alcohol having wiggle room among the public thanks to some poor studies.

Just about every other piece of nutrition advice out there can easily be categorized as controversial. Not in the sense that one side is obviously stupid or malicious, but in the sense that both sides earnestly think they are right.