In this day and age of extremely restrictive fad diets and allergies, it is important to think about these things when you are picking a menu. Half the battle is knowing. So the first step is to throw it out there and see what you are working with. The best way to do that is to add a written section on your invitation, asking not only if your guest wants chicken, beef, or a vegetarian meal. Also, are they gluten-free, dairy-free, allergic to lemons, or whatever is the new thing or personal restriction. Knowing this ahead of time, you and your cater can make adjustments to the menu. So let us say if most of your guests are gluten-free. For one of your sides, you could choose polenta (corn) instead of risotto (pasta) and a gluten-free sauce. This will eliminate one substitution this way any surprise restrictions will already be covered.