As someone with celiac disease myself, food allergies and intolerances should be traits, but food and vegetable choices that don't depend on getting sick or not getting sick, should be likes and dislikes, including strongly like, like, neutral, dislike, strongly dislike. Vegans would be strongly dislike meat, and would get related moodlets just like the child of the ocean if they accidentally ate it. Vegetarians would dislike and avoid meat, but there are also subgroups of vegetarians: ones that eat dairy, ones that eat eggs, a few that only eat seafood (nothing with a face). Then there are those on the no-red-meat diet. And the ones on the no-sugar diet. And the ones on the low-sodium diet. Considering certain actual health conditions, there could be a chance card that a doctor advises a certain diet is needed for the Sim to stay healthy. After that, side effect moodlets show up after eating the banned foods, but if it is a food the Sim likes, the Sim will also get a mild sad moodlet when they have not eaten it for awhile (similar to the ones that the materialists have when they haven't bought anything new for awhile).
On the other hand, foods like soy milk, kale, protein smoothies, watermelon sweet pickles, veggie burgers, or other disliked foods would give a "that's disgusting" moodlet, or if eaten the first time, "what did I just eat" just like the neighbor's fruitcake.
