Hm, I've never really used this, but I just took a look at it from your question.
I don't see a place to subscribe under "Recommended items," however you do have a button to subscribe to the individual feeds that are under "Recommended sources."
This may help you though, if you click "show details" in the upper-right corner when viewing "Recommended items" you get the "Feed URL," perhaps you are able to subscribe with this URL?