As a long-time host, I've learned to ask up-front of someone has any food preferences or limitations...perhaps that should be in the profile, although to be honest, I usually get called on the phone and do not check the profile before inviting them on in, and do not usually know their username.
Of course, that brings up the second part of this: How you either bring it up without looking like you're assuming you're invited for dinner (which you always are at my house), or risking offending your host and going hungry by announcing "I'm vegan" over a steaming plate of spaghetti and meatballs; this actually happened to my wife one night when I was out of town, the kid was just lucky that she had some Ramen noodles and mushroom soup handy. Moral is, if you have any sort of food restrictions, find some way to let the host know that...whether it is religious, ethical, or allergy-related, I know that we will be more than happy to accommodate a reasonable deviation from our normal diet as long as we know in advance and I'm sure that at least some others feel the same way.
The other part of this issue (and hte part which I will be dealing with as a newbie guest) is how to ascertain your supper plans without being pushy or making any assumptions. I've only dealt with this once and was curious about how others deal with finding out if you should eat before you get somewhere. The one time we've stayed with a CS host, I called her on the phone and asked her for a good place to eat on the way to her house so that we didn't all show up starved. I figured this would give her a good opportunity to either invite us to eat with her or gracefully not invite us without saying so or being put on the spot...which she did as she told us about her favorite Chinese buffet. To be honest, considering that we had 5 hungry teenagers with us, I don't blame her! LOL
I would think that as a cyclist, asking for directions to the grocery store on your way to their house and for permission to use their microwave would accomplish the same result of broaching the subject without anyone feeling awkward...until I'm told otherwise, I would assume that I'm not invited and proceed accordingly.