I was at a seminar about gut bacteria recently and the book 'The Psychobiotic Revolution' by Scott Anderson, John Cryan and Ted Dianwas was highly recommended. It is up-to-the-minute research on the gut-brain axis. It is a wonderful insight on what is going on in our gut and how it can affect our mood. It also shows us how we can help ourselves when we are experiencing depression or anxiety by nurturing our microbiome. Although Cryan and Dinan have PH.Ds in the field, it is written so we can all understand it. I highly recommend it.