Gut bacteria have been linked to mental well-being and depression. People who lack two particular bacteria, Coprococcus and Dialister, are more likely to be depressed, and those who have normal levels of them report a higher general quality of life. Coprococcus is associated with dopamine signaling, and it also produces butyrate, a fatty acid that is an important anti-inflammatory agent; increased inflammation has been linked to depressive symptoms. A third bacterium, Faecalibacterium, also produces butyrate and is found in people who report a higher quality of life.
