The gut microbiome is a crucial factor for good sleep: lots of deep + REM sleep https://www.derstandard.at/story/3000000300353/warum-guter-schlaf-im-bauch-beginnt Good sleep starts in the gut https://theconversation.com/good-sleep-starts-in-the-gut-270487 The gut is involved in the conversion of serotonin to melatonin. The calming neurotransmitter GABA is produced in the gut