From the Cunard website-
We will make every effort to meet your dietary requests for low-sodium, low-fat, low-sugar, lactose intolerance, dairy free, gluten free, wheat free and vegetarian diets. However, please be aware that our chefs are not medically trained.
Please ask your travel agent or contact Cunard customer contact centre directly on 0345 355 0300* to inform us of other special dietary requirements. Whilst every effort is made to ensure that special dietary requests are met, this cannot be guaranteed.