May I ask what are the actual symptoms,I know he is vomiting and Diarrhea has he a fever , is he sick enough not to go to work ?There are some virus's going around ..I think he should be checked out if it is still happening.Make sure he drinks plenty of water .
You can't rule out food poisoning. If he is and keeps vomiting, diarrhea take him to urgent care/ dr.
My husband is on a very strict diet too (because of me), and he does finds that if he really indulges in all the fatty food I never make (eg eats a whole meat lovers pizza by himself) he feels really bloated, nauseated, and then has one really bad poo. It's mainly because he's not used to eating so much fats and his body seems to overcompensates for it. However he has to go out of his way to eat that amount that makes him sick, so I doubt your husband's problem is because of his new diet. (Unless he went crazy on the beer/dairy).
Although I guess it is possible that he himself had gluten issues that was ignored. After not having them for a while, his body becomes less irritated until it sees it again and then it over reacts. Maybe he needs to be tested for food intolerance?