In reality, when hosting, I find that food issues are very easy to accommodate. Most people take the stance that they can eat anything when they're a guest in some one's home. Some of my friends have actual food issues and we accommodate them without a problem - dairy, gluten, allergies, vegetarian, etc. Perhaps it's because we're an international couple and have a wide range of dishes we can make between the two of us, but I just don't find it to be that big a deal.
The people who truly can't eat much of anything usually bring their own food - my SIL's sister is on some raw food, all organic, vegan kick with categories of vegetables that are also excluded for I don't know what reason. She comes to our holidays, picks the few items she can eat of what we've made, eats plenty of whatever dish she's brought to the party, and seems happy about it. We don't consider her rude and she doesn't seem to think ill of us either.
But here on DCUM, or in theory, if you list out all the possible food issues a set of guests might have, it sounds impossible. I just don't find that to be the case. Most of the time, you can accommodate your guests and when it's not possible, the guests know that and they take care of themselves.