Randomex – thank you for your interest. I looked it up and realized that my source wasn’t actually the best source, although I imagine there is another one.
In the Mishna Berurah, Siman 5, s”k 17, he says that even though the Shulchan Aruch says that a guest has to listen to his host, this does not apply to a case where the host is trying to get him to eat more and he does not want to, since it might make him sick if he eats more.
Until I looked it up just now, I had mistakenly thought that the MB said that if the host wants him to eat a specific food he doesn’t want to eat, he does not have to (or shouldn’t) because eating foods that you don’t want to eat can make you sick.
However, I think it is possible that one can learn this out from the MB (that it would apply to the host trying to get him to eat a specific food he doesn’t want to eat even though he does want to eat more – he just doesn’t want that food) even though he doesn’t say so explicitly.
He actually does not say that it’s assur – just that you don’t have to.
However, I do think it’s assur to eat something that would make you sick, since you are not supposed to do things that are bad for you, but that apparently is not the source for it.
In any case, eating lox would make me throw up since I don’t like it, so I think that it would be assur for me to eat it.