system
Given the following post, respond as if you're commenting on Reddit:
human
How can an almond help with digestion but also be indigestible?

Apparently it's called "roughage". It is "fibrous indigestible material in vegetable foods which aids the passage of food and waste products through the gut" which for example can be an almond. How come there are so many whole grains, nuts, seeds, legumes, fruits, and vegetables, that your body can't digest, but also helps digestion? To the uneducated mind, it sounds like an oxymoron.
gpt
Fiber helps with digestion by absorbing water, which softens/loosens feces.

There are three basic components to digestion in the body:  Propulsion, chemical/physical digestion, and absorption. Fiber helps with propulsion, but cannot be broken down properly by the body and thus can't be absorbed. Which means that it aids in the digestion of other nutrients, but can't be digested itself.