Tell 'em to bring their own food
In all seriousness, a version of that suggestion might be the way to go. Even if it's only to suggest they provide you with menus, ideas, etc. The low/no carb area particularly is probably difficult for those that have no idea what it entails, as it does require research etc.
I don't think you can be expected (depending on your own skills, knowledge, etc) to provide such meals so a conversation of some form is probably a good idea. They might even be happy to wave their rules for their duration of stay with you. You won't know unless you ask.
Edit: I think I may have misread. We're talking one meal rather than a week of?