For most of us, getting “butterflies” or even a stomachache before an important exam is nothing unusual, but what if this feeling actually reflects something deeper? What if the cause of our worries is physiological rather than just psychological? Emerging research suggests that the gut plays a far more significant role in emotional wellbeing than previously imagined, with direct links to conditions such as anxiety, depression, and even schizophrenia.
Often referred to as the body’s “second brain”, the gut has long been associated with instinct and emotion, and our recognition of this association is even present in everyday phrases like, “trust your gut”. However, scientifically, this idea is only now gaining credibility, all thanks to our understanding of the gut microbiome. The gut microbiome is composed of several species of microorganisms including bacteria, yeast, and viruses. These microbes are increasingly being linked to brain function and mental health. Numerous studies have identified the role of the gut in neurological disorders such as Parkinson’s disease and Alzheimer’s disease, as well as in psychiatric disorders such as anxiety and depression.
This recognisable connection between the brain and gut is primarily explained through the gut-brain axis!
But what is the gut-brain axis and why is it so important? The gut-brain axis is a complex bidirectional communication network that links the gastrointestinal system to the central nervous system. This communication occurs through various crucial pathways, including the vagus nerve, hormones, and even immune signalling. Through these mechanisms, the gut has the ability to alter neurotransmitter production, immune responses, as well as inflammation, which are all factors that influence mental health.
An imbalance in the gut microbiome, clinically known as dysbiosis, has been associated with several neurological and psychiatric conditions, including anxiety and depression, as well as bipolar disorder. These conditions are proposed to be linked to chronic inflammation, suggesting a potential pathway connecting gut health and mental wellbeing.
The worldwide prevalence of mental health conditions highlights the importance of this research. According to the World Health Organisation, there are approximately 359 million people living with anxiety and 332 million people experiencing depression, making the investigation of factors contributing to their development imperative. Interestingly, gastrointestinal conditions such as irritable bowel syndrome (IBS) are often observed to co-occur with anxiety. Research suggests that gut inflammation in those with IBS may send signals to the brain through the gut-brain axis, influencing mood and behaviour.
Another crucial link lies in serotonin, a neurotransmitter commonly associated with mood regulation, also known as the “happy hormone”. Research has demonstrated that the gut is responsible for producing 90% of the body’s serotonin, emphasising the connection between the gut and psychiatric conditions such as depression, which have been associated with low levels of this neurotransmitter. Depression is also increasingly being viewed as a systemic inflammatory disease, and individuals with the condition are observed to exhibit higher levels of pro-inflammatory cytokines, as well as reduced gut microbiota diversity. Research also highlights a decrease in beneficial bacteria like Lactobacillus in individuals with depression.
In recent years, certain probiotics have also been called “psychobiotics” , a term initially introduced by Ted Dinan and John Cryan. They defined psychobiotics as live organisms, which produce beneficial effects for psychiatric illnesses when ingested in adequate amounts. This specific class of probiotics was further defined as bacteria that are able to produce and deliver neuroactive substances, including gamma-aminobutyric acid (GABA) and serotonin, both involved in nervous system regulation by producing a calming effect.
Pre-clinical trials conducted by Dinan and his team in 2013 showed that certain psychobiotics possess antidepressant or anxiolytic activity. The underlying mechanism for these results remains to be fully explored; however, it is proposed that psychobiotics modulate inflammation, stress responses, and neurotransmitter production. Although further research on psychobiotics is still required, they may be the key to discovering treatments targeting mental health through the gut!
While this field is still developing, it represents an exciting frontier in neuroscience. Understanding the relationship between the gut and the brain may open up various new avenues for treating complex psychiatric conditions, many of which have limited treatment options available as of today. While this field holds immense promise, more research is needed to understand these connections and translate them into effective treatment targets.
