The problem I have with diet research is that the studies (and the internet commenters) are always looking for one thing that everyone can do and get good results.

The body is a complex system, and different people's bodies work differently. Really, what I want to know from a diet study is were their negative effects, and did it work for a significant amount of the people. Ideally, for those who it seems to work, do a longer term study to look for negative effects and long term results for people who stick to to it. If you get enough of these studies, and I'd like to change my diet to control my weight, I can try things until I find one that seems to work for me, and have some confidence that it works long term for people who it works for.

One diet to rule them all is the same thing as everyone should run the same HTTP server. I love apache, but different systems work better with different servers.