That’s true, the gut and the brain are tightly linked and are in constant communication with each other, an obvious example is hunger for example.

I felt the need to comment this because serotonin and dopamine produced in the gut have completely different functions from the dopamine and serotonin in the brain. On top of that the body keeps those completely separate with the blood brain barrier so it can regulate those different functions individually.

The gut does play a part in tryptophan production and extraction which passes the blood brain barrier and the brain uses to make serotonin so the gut does affect serotonin levels. But that’s just “eat healthy, feel good” type of stuff.

I’m just not a fan of oversimplified version of this where people say “90-95% of serotonin is made in the gut, serotonin is the feel good hormone so gut affects happiness”. I mean, most people are aware that what you eat affects your mood but saying the gut is responsible for producing the hormones for the brain is just wrong when talking about dopamine and serotonin.