Gut Feelings
The human microbiome refers to the collection of bacteria, single-cell organisms, viruses and fungi that co-mingle in your gut and intestines and they are linked to a wide range of human health conditions, including digestive health and the prevention of autoimmune diseases. Indeed, research has also identified a possible link between gut health and brain function.
It has been shown that people with major depressive disorder, their microbiome differs from that of people without a depressive disorder, with several species missing. Indeed, when the mix of bacteria that are in there are transplanted into rats, the rats become depressed. However, what the research has not been able to establish is if poor mental health causes depletion of the bacteria or if the missing bacteria intensifies symptoms associated with mood disorders.
It appears that almost all gut bacteria are able to produce neurotransmitters, which are chemicals that enable communication between neurons. Oddly, though, bacteria outside the microbiome do not appear to produce neurotransmitters, indicating that this is some sort of evolutionary adaptation and perhaps there is some sort of symbiotic relationship between the bacteria and the host - us!
The body's longest nerve, the vagus nerve, runs from the stem of the brain to the lowest part of the intestines. It is a dual-carriageway for information sending signals from the brain to the gut to regulate digestion and bringing signals from the gut to the brain. It is this latter way that could facilitate neurotransmitters produced by gut bacteria influencing mental health. In particular, two bacteria genera, Coprocouus and Dialister, are depleted amongst people with depression. However, it is not just a question of increasing the levels of these bacteria in the gut to relieve symptoms of depression as different species even in the same genus (family) can have different results - Dialister has species where one type reduces the risk of depression whilst another increases the risk of depression.
Notwithstanding, there is a huge amount of research in this area now and whilst the benefits to human mood and quality of life could be enormous the complexity of this research is massive - only in early 2019 over 100 new gut bacteria were discovered in the human microbiome!
