What does one do in this situation?

I’m attending a catered for dinner party tomorrow night. Several of my friends are going. One of my friends has invited himself over for lunch; so I’m reheating my best diet dinner, for his lunch, chicken parmigiana with potatoes and mixed vegetables. My friend is a big eater. I’m less so. However they weren’t specific about the amount of food we’re getting at the party. I’m also trying to watch my weight. Should I eat a big lunch, too, or have a smaller lunch, wait for dinner?

What does one do in this situation?
Post Opinion