system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If it takes 24-72 hours for food to digest, how come sometimes you can eat bad food and get diarrhea 5 minutes later?
gpt
When the body detects something so bad that it needs to expel it ASAP, it can either go up (vomit) or down (poop). 

When you get sudden onset diarrhea, it isn't necessarily the food that you just ate that is coming out your butt.  The body is trying to get rid of the bad stuff in the gut....so all the stuff already in the system is hurried along.