It seems like every culture expects guests to want to eat regardless of their circumstances, and if you refuse, you’re automatically rude and insulting.
If I offer you food and you refuse, I’m going to be quite happy. It means I get to save money and have more food to myself. I ain’t offering a second time if you say no the first time :maduro-coffee:
you can refuse but doing so you should say that you are too full and performatively bemoan the offered food.
at least that works in my experience