For nutrition in particular, I actually think epistemic techniques would be useful. The whole diet/exercise/weight loss cluster is a bit Wild West. I've read commercial gurus (who tend to be unscientific) and peer-reviewed studies (which tend to show a lack of practical knowledge, typically in that the "test" diet or exercise is often nowhere near as intense as what actual fitness buffs do.) Being aware of cognitive biases and having some crackpot-detecting mechanisms would actually be useful.

Incidentally, since I realized that it can be hard to find suitable non-political examples for use here, nutrition might be a good substitute for climate change in examining how to look at "scientific consensus."

There's nothing wrong with basing your rationality on actual data, and I'd say it's a useful practice.

As LW gets larger, we may want a split between general theory of rationality, longterm speculation, and practical application, just to give people more tools for finding what they're interested in.

Sure, but nutrition claims to be a science, and they don't break obvious rules of rationality.

I don't agree with your assessment. That is to say, I accept the 'science' part but not the 'rationality' part. Nutrition is based on politics, with the rational-rule breaking that politics entails.

Now, I don't have any confidence in any of their conclusions, but to do better would require more than mere philosophical sophistication; one would have to go out and gather actual data.

There is quite a lot of evidence that they have been rather bad at updating based on the data that has been collected.