The gut microbiome includes bacteria, bacteriophages, viruses, fungi, protozoa, and archaea, and this community of organisms is critical to the maintenance of human health, as well as in the pathophysiology of various diseases. The community in your gut is unique, much like your fingerprint. They began to colonize you the moment you were born and can change throughout your lifetime. Good bacteria in your gut help you absorb nutrients from your food. They also take up space and hog vital nutrients so harmful microorganisms are not able to colonize and educate immune cells in the identification of harmful invaders.

However, did you know that your gut microbiome also affects your mental health? These tiny beings help you break down food traveling through your intestines, hence producing metabolites influencing all your cells – including those of your nervous system. Simultaneously, immune responses to harmful pathogens produce molecules that can also affect brain physiology. But that’s just scratching the surface. A healthy and diverse microbiome is essential for normal cognitive and emotional processing. Your microbiome communicates with the central nervous system – aka the brain and spinal cord – through nervous, endocrine, and immune signalling mechanisms. We don’t yet have a good understanding of how the gut microbiome and central nervous system influence one another, but it’s been shown that changes in gut flora composition can result in increased intestinal permeability, allowing neuroactive compounds through and activating the inflammatory response. Yet other microbiota can produce compounds that affect gene expression in the nervous system. Research has shown that changes in microbiota can cause depression, change social interactions, protect from stress-induced changes to the immune system, and can cause physiological changes that are even transferable between species! 

Our lifestyle has a major effect on the composition of our microbiome. What we eat, our stress levels, and our emotional state determine which organisms can live on in our gut. The human gut microbiota is generally fairly stable, and resists change in community makeup. However, the brain can modulate the composition of our gut community by changing intestinal permeability and secretions, as well as through the release of hormones that affect microbial gene expression. Our gut flora composition can also be perturbed by changes in hormones or diet, antibiotics and stress. Reduction of the normal gut biota population – for instance while taking antibiotics – provides an opportunity for pathogens to colonize the gut epithelium. It has been known for a while that the gastrointestinal system communicates with the brain. The enteric nervous system is a mesh-like set of 500 million neurons governing the gastrointestinal tract. That’s 5 times as many neurons as there are in your spinal cord – no wonder the enteric nervous system is sometimes called the second brain! The enteric nervous system CAN operate autonomously, however, it communicates with the central nervous system via the vagus nerve and prevertebral ganglia. 

This biochemical signalling between the gastrointestinal tract and central nervous system is called the gut-brain axis. However, it is only now being realized just how much of an affect the microbiome has on the brain. Hence, this bidirectional interaction between the microbiome and the central nervous system has been termed the microbiome-gut-brain axis. The gut microbiome and central nervous system have bidirectional effects on one another. 

More research on this topic will help us get further insights into disorders of both the gut and the central nervous system. This is exciting news, because perhaps neuropsychiatric disorders will one day be treated through gut microbiota! Preclinical studies have identified plainly the powerful influence of gut microbiota on the central nervous system, but there are still issues with reproducibility, so we need continued improvement of experimental approaches. 

So, what can you do to maintain the health of your gut flora? Eat a healthy diet tailored to your unique gut flora composition.