I'm gonna be fairly brief today and draw your attention to yet another systematic review and meta-analysis this time looking at how "probiotic supplementation can have a positive effect on mood and psychological symptoms such as depression and anxiety."  Probiotics by the way, include a variety of bacteria and related lifeforms that are thought to confer some health advantage.
The review/re-analysis by Jennifer McKean and colleagues found 7 studies on this topic in the peer-reviewed research literature, that overall "showed that supplementation with probiotics resulted in a statistically significant improvement in psychological symptoms... compared with placebo." Personally, I wasn't surprised at these findings having covered a few bits of science on probiotics and psychology before on this blog (see here for example). Some recent discussions on how probiotics might be a possible 'stress-reliever' (see here) also add to this area.
I know some people are still a little sceptical of the whole 'gut-brain' thing (i.e. what goes on in the gut might have the ability to influence what goes on the grey/pink matter floating in the skull) and all the associated 'hype' that has accompanied the new science around the gut microbiota including the use of probiotics. There is lots more to do in this area; also overlapping with how other interventions may more detrimentally affect the trillions of bacteria that call us home and onwards may have 'psychological consequences' too (see here).
But it is getting rather more difficult not to think that there may be some important processes at work in these times of psychobiotics ...
 McKean J. et al. Probiotics and Subclinical Psychological Symptoms in Healthy Participants: A Systematic Review and Meta-Analysis. J Altern Complement Med. 2016 Nov 14.
 Dinan TG. et al. Psychobiotics: a novel class of psychotropic. Biol Psychiatry. 2013 Nov 15;74(10):720-6.
McKean J, Naug H, Nikbakht E, Amiet B, & Colson N (2016). Probiotics and Subclinical Psychological Symptoms in Healthy Participants: A Systematic Review and Meta-Analysis. Journal of alternative and complementary medicine (New York, N.Y.) PMID: 27841940