system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does the body do to suppress the appetite when food is not available?

I ate a normal breakfast this morning but was in a work meeting from 11-6 where food was not available. Instead of being hungry for lunch at 12 or 1 like usual, I wasn't hungry at all. I recall other unexpected situations where food wasn't available yet it seems like my body did something to suppress my appetite. What is my body doing, and how does it know to do it?
gpt
This may not fully explain the matter, but one element at play is your body’s sympathetic nervous system, also known as your fight or flight response. It’s counterpart is the parasympathetic nervous system, also known as the rest and digest response. 

These two are always competing with each other and neither is a simple on/off switch, they’re spectrums. So when your sympathetic system is winning the tug of war your body doesn’t care much about eating or signaling hunger. 

Sympathetic activation does not only occur in emergencies. It kicks on with any stress- even just a really busy day at work.