A few reasons.
An easy thing to understand is that it breaks up your poop giving it a good consistency. Stops your poop from being either pasty, or rock hard.
The other part is that while you can’t digest it, the bacteria in your intestines can. They actually help regulate the production of chemicals in your brain in the long run, so it’s good to keep em healthy!
The above is also one of the reasons why fermented foods are good for you as well, and really why diet is important to your over all health (mental and physical) in general; help that gut biome help you!
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