My spouse has food sensitivities to things my parents frequently cook including tomatoes and nuts. These sensitivities don't put them into shock, but do cause sensations of pain and discomfort. In a lot of ways, my spouse comes off to my parents as picky, which isn't exactly the case. The only "picky" behavior is my spouse's aversion to shellfish, which is a texture thing. My spouse also doesn't eat much in the way of sweets, which my parents love.
My mom cooked a pot of gumbo which contains tomatoes and shrimp and is most likely going to serve bread with nuts as a side, start with a salad with tomatoes and dressing with items my spouse is sensitive to, and end with a desert of some kind. This would mean that my spouse wouldn't be eating any salad, not eating the gumbo, not eating the side, and not eating the desert.
How best can I convey to my parents that my spouse probably cannot eat any of the items being served without conveying pickiness?