Spinach, that's interesting. Apparently, tryptophan + vitamin B6 + vitamin C converts to serotonin.
https://thomasmcgregor.wordpress.com/2013/06/07/cure-depress...
https://thomasmcgregor.wordpress.com/2013/06/07/cure-depress...
I most often eat it first thing in the morning as a shake: 90g spinach + 1 cup almond milk + half a frozen banana.
According to the article, I may want to add some strawberries or oranges for more vitamin C.