The thing is, its not as if r/fitness or /fit/ invented the low-carb diet or the paleo diet. They just spread it to people who'd otherwise never engage in debate/discourse about nutrition (which is of course commendable.)
> It's the perfect meritocracy of ideas, and the slow peer review process can't keep up.
I think Reddit and blogs have seen enough false witch hunts and outright lies to know that the internet is very, very rarely a meritocracy. Peer-reviewed processes aren't meant to serve as a proxy for the general population, or to spur rapid progress; in fact, their goal is serve as objective judges of validity and accuracy.
This is somewhat akin to when people complain about the difficulty in passing legislation in the U.S. Things like bicameral legislature and checks and balances were instituted specifically to slow down the passage of legislature and allow a more deliberate review process.