A summary of the diet/nutrition literature which sorts the well-established points from the chaff would be extremely useful. Is there already a comprehensive online user-friendly treatment, written by extremely rational thinker(s) who have done thorough research? I would be surprised. The area is a minefield of cleverly disguised bad research.
How will people be able to tell that you've done the job well?
My feeling is that there is generally very impressive rationality on the market in fields of endeavour where you will quickly get a clear answer on whether you were right, and so it's hard for rationalists to show off their skills there. But when you start to compete outside of those fields, no-one can tell that you're doing better.
Holden Karnofsky of GiveWell.org interviewed Jasen Murray of SIAI and published his notes (Edit: PDF, thanks lukeprog!), with updates from later conversations. Lots of stuff to take an interest in there - thanks to jsalvatier for drawing our attention to it. One new bit of information stands out in particular: