Dr. Michael Greger made this video talking about a study in which 2 kwiwi fruits at night helped with insomnia.
The supposed method of action was that kiwi contain serotonin. However, the video mentioned that serotonin should not be able to cross the blood brain barrier. But if most of the serotonin is produced in the gut, then how does it get to the brain? Perhaps serotonin has other actions outside of the brain?