Dinner invitation

Certainly this must happen to you. Tonight we are invited to dinner at a friends home. They have excitedly told me last night that they are serving their special pasta dish, a recipe passed down from their grandmother. Short of being rude…yes,
I know you wont agree it would be rude, what would you do? I know what I am going to do…be polite and eat a small portion and keep my eating program to myself. The last time I Was at a friends and mentioned that I didnt eat certain foods I was told in no uncertain terms that when you go to someones home you politely eat what is served to you. It was very embarrassing. I turn down many invitations but cannot turn them all down. No, I wouldn’t smoke if offered but I don’t see this as the same thing. I am near my goal weight, most people tell me
I am looking “to thin”. I really dont want to appear like a zealot. Just curious as to how you handle these situations. Stay home?? Bring your own food? This needs to be a lifestyle not a diet. I need to know how to handle these invitations.