system
Given the following post, respond as if you're commenting on Reddit:
human
Why do you not feel hungry after not eating for a long time?
gpt
In short, adrenaline and cortisol. If you haven't eaten in a long time, your body doesn't relax, it instead increases stress hormones which induce the metabolism of energy stores (ie, fat tissue, glycogen) and help mobilize you so that you can find food or fight for it. 

Once you eat, stress hormones decrease, blood flow to the intestines and visceral organs is restored, and you feel hungry again (this is why appetizers induce appetite).