Can you speak to the administrative staff person before you get there? There must be an admin person who is calling you and setting things up, right? the search committee isn't calling you directly are they? If so, could you call the admin person and just tactfully say you have some specific foods you can't eat (she/he will assume diabetes/allergies, vegan, whatever) and ask what is for lunch or suggest that a chef salad would work for you or a broiled chicken breast with ceasar salad (no croutons). Give a couple of options. Better to have it organized in advance than to fret about it or find out you are getting served a pasta dish or something else you can't eat for lunch.

Good luck!