Serotonin Starts in Your Gut

Most of your serotonin is made in the gut by specialized gut-lining cells, not by the brain. That serotonin matters for digestion and gut signaling, but it does not simply cross into the brain and become your mood.

The food-to-mood route is more indirect: gut microbes, inflammation, the vagus nerve, and dietary tryptophan all shape the gut-brain axis. Tryptophan still has to cross into the brain before brain serotonin can be made.

That is the real comfort-food effect. Refined carbs spike then crash, leaving you lower than before.