system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is fiber good for you, and what exactly does it do when you eat it?
gpt
Fiber=carb that body cannot digest.

soluble fiber can dissolve in water.  It can help regulate the amount of "bad" cholesterol in your body. 

Insoluble fiber can't be dissolved in water.  It helps move food through your digestive system and helps you form poops that are easy to pass so you don't get constipated.  Also, foods with a lot of insoluble fiber can help you feel full without as many calories because it's adding bulk to your food.

High fiber diets have also been associated with lower risk of some chronic diseases.