‘A Gut Feeling’
What is the gut-brain axis?
• The two-way or bidirectional communication link between the brain and the intestines.
• It is mediated by the gut microbiota and the small molecules they produce.
• These are recognised by receptors in the brain that allow the gut to influence many factors such as our emotions, stress, immunity and appetite.
The Human Microbiome:
The human microbiome is the population of microbial genes (bacteria, fungi, protozoa and viruses) that are found in the skin, mouth, nose, vagina and mainly the gut of the human body. The genes in our microbiome outnumber the genes in our genome by 100 to 1 and unlike the human genome which is fixed for life, our microbiome changes over time.
Bacteria-Human Symbiosis – It’s teamwork!
These microbial populations live in harmony with the human host and are essential for human development, immunity and nutrition. However, they in turn can be influenced by host environmental factors such as diet, lifestyle and our health. For example, autoimmune diseases such as diabetes and multiple sclerosis are associated with a dysfunction in the microbiome. The diseases cause certain microbes to accumulate over time, changing gene activity and metabolic processes and resulting in abnormal immune responses against substances and tissues normally found in the body. Obesity has also been associated with a poor combination of microbes in the gut.
The Gut-Brain Link:
The bacterial genes that live specifically in our gut make up the Human Gut Microbiome. These bacteria and their metabolites can send signals to the brain via the gut-brain axis. This is the bidirectional communication system that links the emotional and cognitive centres of the brain to the intestines and vice versa. For example, bacteria can release signals in the form of small molecules that molecularly mimic and/or trigger the release of certain hormones into the blood stream. These are recognised by receptors in the brain and can trigger a neurological response such as stimulating emotions or controlling appetite.
This link can be seen in the association of gut microbiome dysbiosis with central nervous disorders and functional gastrointestinal disorders. Understanding this link in more detail will unlock the potential for many new targeted microbiome therapies.