At the wedding I was served chicken cordon bleu, asparagus, and rice pilaf. Great food if the diet wasn't an issue. But since it was, what does a person do? Well, first thing you need to know is that you alway have a choice on what you eat. In a case like this you should stick to the asparagus and chicken. The rice is something that you don't really need and its just added carbs. And guess what, it never hurts to ask your server. Most places like this can at least provide a salad. They want you to be happy at the event so that you tell your friends and the caterers may get more jobs in the future.
Just remember, If you can make it through the night you'll be in good shape. Just beware the cake. You will be surrounded before you know it.