What if I told you there was some truth to the old saying ‘gut feeling’? Expressions such as ‘go with your gut’, ‘trust your gut’ and ‘intuition’ have persisted for a reason:
there is a biological/physiological basis for them
Turns out our gut can be a source of sensory feedback; we are able to perceive things subconsciously before our conscious minds does and we’ll feel it – where else? – but in our gut and this is no accident. Our digestive tract and our central nervous system [brain & spinal chord] are intimately linked and you can’t have optimal health of one at the expense of the other. Enter the gut-brain axis
What IS the gut-brain axis?
Generally speaking, the gut-brain axis refers to the bidirectional [both ways] communication that occurs between the brain and the gastrointestinal tract, or “gut”, as well as, other gut-related organs like the liver, stomach, pancreas and gallbadder.
Not only does the brain communicate with the gut and affect how the gut works, the gut, in turn, affects the activity of the brain, including mood, in a ‘bottom up’ fashion.
Communication between the two is mainly through the vagus nerve; one of the cranial nerves that extends down the spinal chord from the brain through the neck, chest and into the abdomen and digestive tract. The vagus nerve is made up of about 80 to 90% of the afferent nerves which are responsible for sending information from our five senses (sight, touch, taste, smell and hearing) back to the central nervous system or CNS (brain and spinal cord) for processing.
What may surprise a lot of people is the fact that the gut also has its own network of nerves called the enteric nervous system or ENS. It’s estimated that the brain has between 84 to 86 billion neurons whereas the gut about 1/1000th as many or about 84 to 100 million.
Embedded in and along the digestive tract , the ENS acts independently of the CNS (brain & spinal chord). Research has demonstrated that if the vagus nerve is severed, the ENS keeps chugging along, running it’s own show and is capable of communicating with other parts of the body via its own production of hormones, peptides and neurotransmitters*.
Even if you haven’t thought about in terms of the gut-brain connection, you’ve absolutely experienced it. Everyone has had butterflies in their stomach; that sense of nervousness you feel in your tummy just by anticipating something in your mind that causes anxiety or fear – public speaking anyone?
While most people think that the brain is the command center, overseeing all bodily functions, regulating emotions and mood while processing all of the information coming in from our five senses, study after study has confirmed that the gut can do much of the same: learn, remember, perceive sensory information, and produce emotion-based feelings too. In other words, that ‘gut feeling’.
It is for this reason that the gut is often referred to as ‘the second brain’.
What about the microbiota?
Another key player in the gut-brain axis is our microbiota; the trillions of bacteria that reside in the gastrointestinal tract which are critical for immune function, digestion, nutrient production, and overall gut health.
More recently, the microbiota have been shown to influence our mental state too such as our psychological and emotional well-being including our outlook, how we perceive and respond to stress and possibly memory.
The Invisible Universe of the Human Microbiome
How does the gut-brain axis influence health?
In this model, the physical health of the brain, as well as, our emotional and psychological state directly influences the health and function of the gut. Chronic stress, anxiety and depression, as well as, organic brain disease are associated with increased gut permeability [leaky gut], increased gut inflammation, decreased intestinal blood flow, altered pancreatic and gallbladder activity. Stress, anxiety and depression can also lead to changes in motility, or the rate at which food moves along the digestive tract, and can cause imbalances to the healthy microbiota increasing the risk for unhealthy bacterial or yeast overgrowth and impaired immunity [1, 2, 3, 4, 5].
In turn, the health of our gut influences the activity of the brain including our behaviour, mood such as anxiety & depression, ADHD, and our general sense of stress response, or how we perceive and react to stressors in our lives, but the bowel/ENS/microbiota interaction/health is also implicated with other neurological disorders such as Parkinson’s for example [6, 7, 8, 9, 10].
As I mentioned at the start of this post, because the brain and gut are connected, you can’t have your best brain/mood health if the health of your gut isn’t in order and vice versa. For all intents and purposes, they are one entity and should be approached as such whenever someone is interested in optimal mood or gut health. An integrative & functional nutrition approach to IBS for example would involve getting to the root cause of the IBS, managing symptoms, healing the gut, reducing inflammation AND looking upstream to the brain to address any health and nutrition-related issues needed to support mental well-being such as the optimal intake of nutrients needed for brain structure and function. Treating health, and by extension the body, in a reductive manner, as isolated systems independent of each other has resulted in dismal success of chronic disease management. The interconnection of the gut-brain-microbiota axis on health perfectly demonstrates this.
*Side bar: neurotransmitters are chemicals [you’ve likely heard of serotonin, dopamine, GABA, endorphins, acetylcholine and norepinepherine for example] produced by the body which allows one part to communicate with another. The brain produces many of these but so does the gut – people are surprised to learn that the gut produces about 90% of the body’s serotonin, and 50% of the dopamine.