A large part of the issue comes down to funding, and a lack of resources to do the kinds of studies that would help answer some of our most pressing questions. Our insistence on making recommendations — without having the proper research to back them up — has unintended, harmful effects.
This seems sort of crazy. Properly understanding what makes for a healthy diet would go a long way in reducing health issues.
I imagine that nutrition research just isn't as sexy as, say, mapping the human brain.