Bacteria have been discovered in our guts that consume GABA, a molecule crucial for calming the brain, and this could help explain why the gut microbiome seems to affect mood. An experiment in 2011 showed that a type of gut bacteria, called Lactobacillus rhamnosus, can dramatically alter GABA activity in the brains of mice, as well as influencing how they respond to stress. Researchers found that this effect vanished when they surgically removed the vagus nerve – which links the gut to the brain.
Cornell University researchers report (2016) they have identified biological markers of chronic fatigue syndrome disease in gut bacteria and inflammatory microbial agents in the blood. The abnormal gut bacterial microbiome in chronic fatigue syndrome patients perhaps leads to gastrointestinal and inflammatory symptoms in victims of the disease.