Recent research from the Karolinska Institutet in Sweden has shown that gut bacteria has a significant influence on the production of neurotransmitters and in neural development.
Genes and signaling pathways involved in learning, memory and motor control were affected by the absence of gut bacteria, highlighting the profound changes that developed in the absence of microorganisms. This suggests that, over the course of evolution, colonization of the gut by microorganisms (roughly 1.5 kilograms) in early infancy became integrated into early brain development. The data suggests that there is a critical period early in life when gut microorganisms affect the brain and change the behaviour in later life. Not only are signal substances like serotonin and dopamine subject to regulation by bacteria, synapse function also appears to be regulated by colonizing bacteria. While this research is still preliminary, what this means is that probiotic supplementation, and consumption of probiotic foods such as yogurt, sauerkraut, miso, kefir, tempeh and others, likely provides significant benefits to our mental health as well as our physical health. Reference R. D. Heijtz, S. Wang, F. Anuar, Y. Qian, B. Bjorkholm, A. Samuelsson, M. L. Hibberd, H. Forssberg, S. Pettersson. “Normal gut microbiota modulates brain development and behavior.” Proceedings of the National Academy of Sciences, 2011.