The theory being that kiwi’s have serotonin and tart cherry juice has melatonin that help you sleep.

The serotonin in your kiwi gets mostly destroyed in you stomach acid. Any remaining amounts that do get absorbed into your bloodstream will never make it to your brain to do anything because of the blood-brain barrier. Only specific compounds can cross this. Your brain can only use serotonin that it synthesizes. Most of it stick in your gut helping to regulate bowel movements.

It might be the antioxidants lowering inflammation, a hit of vitamin c or some sugar leaving you satisfied that helps.