I'm lactose intolerant and allergic to pineapple and found that the option to order the night before was my best option because the chef could modify almost every dish to accomodate me. In addition, we've eaten at specialty restaurants on board and I found that as long as I spoke with the maitre d' at least a day in advance, they could confirm any modifications with the chef in advance (and they always had a special dessert available for me).