Certainly if you want to take a break and enjoy a holiday treat, do so. But watch your portions. Just because you decide to have a piece of cake, it does not mean you need to have a quarter of the cake. Take a small bit, a toddler food portion, if you will.
And feel free to stand your ground and keep your eating to your usual routine. Simply say thanks, but no thanks right now. Usually there is something to eat off of the host's menu. If not, feel free to bring your own and quietly eat that food.
Before and during approaching challenging situations, take stock and review why you are making the changes you are making. This time to review your goals can give you the ability to reset and stay on your path.