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.
The general practitioner that has followed me since I was born whenever I was ill or hurt is someone who has nearly stopped reading anything about medicine since he finished his study and got his job. On his own admission he doesn't even use computers much and doesn't read the research you can find on places like pubmed. He's nearing retirement and I'm going to change my physician (in France you have to declare one to prevent people from hopping to one place from the other whenever they're ill and "paranoid" and save costs to our health care) once I get done with the paperwork, since I am very lazy when it comes to anything that has to do with paperwork. Btw I know all this about him because he's rather talkative and love to waste time once he's done with the check up. One thing that enforced my laziness in looking for another one is the fact that it can be good to have a physician who knows all your health history from the start, even if he's somewhat incompetent.
When you end up with that kind of "doctor" the internet doesn't look so bad.