1950s Advice from "Diet and Like it": Just say "No, thank you."
I have a charming little diet booklet from 1957 called "Diet and Like it." In it I found this advice:
As a guest in a private home, you are somewhat at the mercy of your hostess. But no code of manners calls for accepting a second slice of cake and you can refuse without appearing ungracious. In fact, in this age of dieting, the ungracious one is the insistent hostess.
Have you ever had an awkward moment as a guest when you felt obliged to indulge beyond what you wanted to eat? Or maybe you are like me and have memories of wanting to eat (or actually eating) way more than beyond "polite!"