Steve Rubel of Micro Persuasion explains how he uses Google Reader to data mine RSS feeds for trends and other information:
"Google Reader recently added a powerful search functionality that has made me infinitely better at studying people and their social patterns. Using Google Reader you can now search an individual feed, tag or a folder and get back a total item count, all sorted by date for as long as you have been a subscriber to that feed.
Now that my reader shows a huge cache of posts, I am subscribing to tons more feeds, stuffing them into a folder solely for the purpose of data mining them. It's worth noting that I don't actually read these high volume feeds. Rather, I mark them all as read so they get logged in my feed database and can be searched for insights."
Steve gives a few examples of using this approach on his blog.
I have not had the time to figure out how to use this for health-related research but hopefully I will.
How to Data Mine Google Reader Feeds for Trends. Micro Persuasion.