The human microbiome, which consists of trillions of symbiotic microorganisms, plays a fundamental role in human health. These microorganisms are particularly active in the gut and are responsible for functions such as digestion, production of short-chain fatty acids, and regulation of immune system function (Fig1). Researches have shown that the gut microbiomeplays an important role in mental health, and changes in its composition can be associated with mood disorders, including depression.