There are many studies on "gut bacteria" and behaviour/mood or state of mind/brain (neuriscience perspective)/... I read some but am confused whether 'we' as a 'sentient being' (In Buddhists term with 'sati') are the master of our body (parts) and mind or 'they' (the lives that live on us) are very much influential on us -- in much the same way we human impact our "world".

We have seen how the tools 'we' created can change 'us' - including the 'view' we created can change societies.