system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come when you have an upset stomach, it’s looser or watery stool? You would think things are being digested less, leading to solid in, solid out.

I’m sure there is a lot more too it. However, why would something spending less time in your stomach lead to it being more broken down? It also seems that the more upset your stomach, the more rapid and liquified your BM is.
gpt
A lot of water is added to the food you eat during the initial parts of digestion. Saliva, stomach acid, and the small intestine all add liquid to the food.

The large intestine is where the water is absorbed back into the body, and that takes time. If you're sick, the body doesn't want whatever made you sick to stay in your system, so it gets sent out faster than normal, so there isn't time to absorb that fluid back.