By Abigail Shields, Year 12
I’m sure we’re all familiar with the physical sensations of stress that arise before an imminent test, or the feeling of “butterflies” in your stomach, and even a tightness in your chest. It seems as though the body reacts before our thoughts even make surface, perhaps as though the “gut” knows what’s coming. Most of us have all heard the idiom, “I just have a gut feeling”, but what if this wasn’t just a saying?
But maybe, a manifestation of the existence of a real biological phenomenon whereby the brain and the digestive system are connected by their constant communication. All this is referred to as the gut-brain connection. This is a complex system that influences your entire well-being, including digestion and emotions. The digestive system, as you learn in biology class, contains a special nervous system referred to as the “enteric nervous system”. This system is made up of over 100 million neurons located in the walls of the gastrointestinal tract. It plays a key role in digestion by controlling muscle contractions, the release of enzymes, and blood circulation. Unlike most nerves in the body, the ENS, or Enteric Nervous System, functions autonomously, sensing changes within the body by itself. However, it does so in contact with your brain.
The main pathway between the gut and the brain is via the vagus nerve, which is a large nerve that transmits information from the gut to the brain. Most of these transmissions are from the gut to the brain, but very few are from the brain to the gut. This makes it possible for the brain to be aware of the condition of the gut in terms of inflammation and other factors. The brain is also subsequently able to control digestion, heart rate, and stress response. This Bidirectional Communication can account for pathophysiologic phenomena like slowed digestion or nausea due to emotional distress, or influences of gastrointestinal disturbances upon mental state or very frequently concentration.
Another part of this gut-brain communication system is the chemical messengers, called neurotransmitters, and one of the most prominent of these is serotonin. Serotonin is a molecule credited with the regulation of mood and emotion. It’s a familiar word to most of us, as it’s considered to be the “happiness molecule.” What’s perhaps less familiar is that serotonin is considered to be a “brain chemical,” but actually, it’s produced primarily in the gut by gut bacteria in concentrations of approximately 70% in the human body. Its function isn’t simply to regulate digestion but to affect signals sent to the brain as well. This relates to the common notion that a healthy plate leads to a healthy mood.
These microbes live in the body as part of the gut microbiome, which refers to the large population of bacteria that live in the digestive tract. The microbiome aids in the breakdown of food, supports the body’s immunity, and produces substances that interact with the nervous system. Some microbes are specialised in the production of neurotransmitters such as serotonin, as I previously mentioned, as well as dopamine. Other microbes produce substances that stimulate the nerves linking them to the brain. Any alteration in the microbiome, which may result from food, diseases, the use of antibiotics, or stress, leads to the modulation of the transmission of these signals.
Additionally, the gut is also a major immune organ. Almost 70% of the immune cells of our body are present here, constantly interacting with microbes and in surveillance for threats. Immune signals emanating from the gut can influence inflammation throughout the body, including the brain. Chronic inflammation has been linked to mood disorders, chronic fatigue, and cognitive difficulties, further illustrating how gut health and brain health interconnect.
Imbalances in communication in this gut-brain axis may lead to certain disorders. Irritable bowel syndrome is one such disorder that is accompanied by both anxiety and depression, indicating it might result from inbaéanced messages being sent from the gut about emotional states. The connection between neurological disorders and gut problems is also being researched, as symptoms related to digestion are reported years before the symptoms of the neurological disorder emerge.
In short, recent studies indicate that the gut has myriad more functions in life than being a passive organ for digestion. The gut is actually a microscopic ecosystem that affects the way the brain works, as well as the way the body reacts to stress, illness, or emotions. The discovery of the relationship between the gut and brain has altered the way scientists view health, realising that both mental and physical phenomena are interconnected. Furthermore, this understanding has led to significant scientific discoveries, insofar as it has driven continued research and deeper inquiries into the gut-brain connection.
Works Cited
Clinic, Cleveland. “What Is the Gut-Brain Connection?” Cleveland Clinic, June 14, 2017. http://my.clevelandclinic.org/health/body/the-gut-brain-connection.
Harvard Health. “The Gut-Brain Connection – Harvard Health,” May 21, 2020. http://www.health.harvard.edu/diseases-and-conditions/the-gut-brain-connection.
News Center. “The Gut-Brain Connection: What the Science Says,” 2025. http://med.stanford.edu/news/insights/2025/03/gut-brain-connection-long-covid-anxiety-parkinsons.html.
www.hopkinsmedicine.org. “The Brain-Gut Connection,” n.d. http://www.hopkinsmedicine.org/health/wellness-and-prevention/the-brain-gut-connection.
