In general though, it's not wise to discredit professionals just because they may disagree on certain things in their field. Unless the field is fully understood (I'm not aware of one which is!), you'll see that.
I'd say that the field is quite poorly understood. Here's an article (long!) that kind of sums it up.
http://www.nytimes.com/2007/01/28/magazine/28nutritionism.t....
What's the best advice to take? That from "multiple" doctors, dietitians, or nutritionists. Not some yahoos on the internet.
A second or third opinion reduces the likelihood of errors, while limiting received advice only from those educated and qualified to give it.
I found out that even after that, I'm tempted to try and do some of my own research, and then apply the advice to myself and see how well it works ...