You raise one of the most challenging issues of all. Which is how to know if the advice you're getting is reliable or not. That's one reason why I like to see what is or is not supported by the published research.
Of course, some research is backed by corporate interests and is therefore less trustworthy in my view. I mean, if the Sugar Board published a paper touting the benefits of sugar, I'd be highly suspicious. So that adds a layer of complexity to the whole thing.
One solution to that is to find someone whose work you come to trust over time and pay special attention to him/her (without turning your brain off, either).
Thanks for commenting, btw.
Gary