When hosting pot-luck meals involving friends /other family members, I haven't told anyone what NOT to bring. So whatever healthy/unhealthy stuff they bring, I let them. I don't like being controlling in terms of what food is complementary, etc. As long as we don't up with too much of potato chips or potato salads from multiple folks.

However for serious allergies where a guest would land in the hospital, I would tell invitees, not to bring the "danger" food for the allergic sensitive person(s).

It's just alot easier as a host not to deal with the possibility of any emergency situation at dinner.