No kidding! It may or may not surprise you that your intestines are full of bacteria but (and this is surprising) they weigh more than your brain! And equally surprising is their role in your mental health. The key lies in the fact that these bacteria produce a number of important chemicals as an byproduct of their metabolic processes, such as dopamine, serotonin and GABA. In experimental studies with animals it has been found that key mental processes are negatively affected when the animal has no gut bacteria – for example there are changes in memory and emotion.
You’ve heard of probiotics (bacteria with health benefit) but now the new development is psychobiotics. One study found that a combination of Lactobacillus helveticus and Bifidobacterium longum reduced anxiety and depression in healthy volunteers. This area of research is only just beginning so there are no magic cures as yet. What is interesting is that for a long time bacteria were seen as evil invaders that we needed to be cleansed of but now their health benefits are being recognised. Evolution is a wonderful thing.
You can read more here and in the New Scientist