The Gut Microbiome Affects Human Mood and Behavior

Gut microbiota, including bacteria, have been recently recognized to influence, not just human health, but also mood and behavior. The microorganisms can either produce or degrade chemical compounds involved in signaling pathways associated with happiness, depression, suicidal behaviors, or even aggressiveness. The connection between the composition of the gut microbiome and some of these mood disorders appears to be so strong that many researchers are describing a gut microbiome-brain axis, with projections to almost all the organs in the human body. This chapter includes some examples of mood-altering microorganisms, in particularly those promoting either happiness or aggressive behavior.