Gut serotonin levels, distinct from brain serotonin, influence gut motility and health and communicate with the brain via the vagus nerve.

“Gut 5HT (made possible by tryptophan, short chain fatty acids & microbes) activates your vagus which in turn increases brain serotonin levels.”

“Now, also within the gut, you have chemical information. There's information about for instance, and we'll talk more about this later, how much serotonin is in the gut. You may have heard that 90% of the serotonin in your body is manufactured in the gut. And indeed, it's manufactured in your gut. It plays an important role in gut motility and gut health. The serotonin in your gut is distinct from the serotonin released in your brain. Later, we'll talk about how the levels of serotonin in your gut are conveyed to the brain by way of, you guessed it, the vagus nerve, and your brain in turn, makes different levels of serotonin to impact your mood.”