I myself have to find a balance when accepting invitations to parties. Don’t be afraid to ask the host questions, are you having a sit down dinner or buffet? If it’s being catered will they make any special requests, most people are willing to work as long as you keep it simple.
As for a buffet you can always offer to bring a vegetable dish that works for you and ask what kind of protein dish will be provided or brought. Never feel bad if you have to bring your own food. Another option is to eat your dinner before hand and arrive after the meal has been served. I even suggest going to a restaurant that has options that work for you so you can still have a special evening.
Now for what I find as the hard part, (DESSERT). Now some of you won’t have any issues saying no to a dessert but I’m not one of them. I will often make something that I can take, and if that’s not possible I will settle for a hot cup of fruit tea. You can even try a flavored sparkling water if you crave a bubbly drink. Just remember that saying no to something you would enjoy is hard but it won’t be forever and you will be able to enjoy these foods again, remember that when you’re trying to keep on track that you will be proud of yourself for not eating something that will be counterproductive to your healthy lifestyle or weight loss goals. In the larger picture one or two evenings out of the year is a small sacrifice when choosing to eat healthy and stay on track.