system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we lose Appetite when we are anxious/Nervous?

Always happens and it would be awesome to dig a bit into the science of it as well.
gpt
Much like the 'Fight or Flight' response related to real-world dangers and how we react to them, the brain has a hard time telling difference between a physical threat or a psychological one. 

Anxiety and Nervousness can be as frightening mentally as a dark alley way or a guy with a knife across the street. 

When your body goes into 'Fight or Flight' blood is moved away from the stomach and to areas where it might be used to run or fight, such as the legs or arms. Less activity in the abdominal region and an increase in adrenaline are some of the many causes to losing your appetite. 

TLDR- Your body is allocating bodily resources effectively for a threat it perceives to be real and life threatening, but is really just mental anguish that it cannot differentiate.