The hundred trillion bacteria living in an adult human, mostly in the intestines, making up the gut microbiome, may have a significant impact on behavior and brain health, according to a new paper.

The many ways gut bacteria can impact normal brain activity and development, affect sleep and stress responses, play a role in a variety of diseases, and be modified through diet for therapeutic use are described in a review article ("The Gut Microbiome and the Brain") in Journal of Medicinal Food.

Leo Galland, Foundation for Integrated Medicine (New York, NY), outlines understanding of the relationship between the proteins produced by intestinal bacteria and the human central nervous system - but tread cautiously when dealing with integrative medicine and other forms of non-science based medicine. Just because the US government spends $100 million on it and other forms of complementary and alternative medicine at the National Center for Complementary and Alternative Medicine does not mean you should risk your health on it. However, because probiotics don't seem to do anything, they won't harm you - just don't spend too much money on them.

In the review of other papers, the author outlines current beliefs about how the various mechanisms of the microbiome are believed by other 'wellness' proponents to impact brain function: by stimulating and over-stimulating the immune system, producing neurotoxic agents, releasing hormones or neurotransmitters identical to those made by the human body, or through direct neuronal stimulation that sends signals to the brain.

"The microbiome has become a hot topic in many branches of medicine, from immune and inflammatory diseases, such as Crohn's and IBD to cardiovascular diseases," says Co-Editor-in-Chief Sampath Parthasarathy, MBA, PhD, Florida Hospital Chair in Cardiovascular Sciences, University of Central Florida, Orlando. "Scientists are not only aware of the 'good' and the 'bad' microbes in the gut but are becoming increasingly aware of how they could alter the metabolism beyond gut."