Calling it a second brain is no exaggeration. Approximately 100 million neurons—which is more neurons than contained the spinal cord—are embedded into the walls of the oesophagus, stomach, and intestines, essentially forming a neural network from mouth to anus (1). While this mass of neurons does not contain any conscious thought, it does control the digestion and absorption of food and expelling of waste separately from our brain.
Unloading this dirty business from the brain may be for more than just convenience. According to Professor Emeran Mayer of the University of California, Los Angeles (U.C.L.A.), “The system is way too complicated to have evolved only to make sure things move out of your colon” (2). He says of the information trafficked along the vagus nerve, which is the primary nerve responsible for the regulation of internal organ functions, 90% is carried from the gut to the brain, not vice versa. That is information travelling from your bowels to your head.
So, those butterflies in your stomach are, in effect, a physiological stress response, and we’re learning that many of our emotions may be influenced by the nerves in our gut. In fact, severe depression has been treated in clinical settings through electrical stimulation of the vagus nerve (3).
That’s not all. Many of the same metabolites and neurotransmitters in the brain are found in the gut. 95% of our body’s serotonin—a hormone that regulates our bowels and mood—is in the intestines (4). Too little serotonin in the brain is thought to cause depressive-like symptoms and is why we use serotonin reuptake inhibitors (SSRIs) to increase serotonin levels and improve our mood. Given this brain-gut connection, we don’t know the impacts certain anti-depressants have on our gut. We are learning that medicines that affect the brain often affect the gastrointestinal (GI) tract. For instance, irritable bowel syndrome is a condition that can arise when too much serotonin is in our bowels, a common and direct consequence of taking SSRIs (5).
Gut serotonin also plays a role in bone formation. A study by Nature Medicine found that drugs that inhibited the synthesis of serotonin, lowering its concentrations within the GI tract effectively “cured” osteoporosis, a bone-deteriorating disease in mice and rats (6). While this study used rodent models, it further implicates our second brain to a breadth of responsibilities in the maintenance of our bodies.
And if we haven’t driven home the connection the second brain has to the brain on our shoulders, there is also growing evidence to suggest serotonin is a link between the gut and autism, a neurodevelopmental disorder that affects how someone thinks, feels, and experiences themselves and others in their environment (7). A study published in Molecular Psychiatry found that more than 90% of the sixty-two genes most associated with autism are expressed in both the brain and the gut, and could explain why children with autism often experience GI issues such as heartburn, discomfort and pain (8).
So, our second brain is controlled by one of the biggest nerves in our body, contains the bulk of the neurotransmitter that regulates our mood, and shares most genes associated with autism spectrum disorder. It should now be clear how important it is to take care of these neurons. And we can begin by knowing that they are directly influenced by the microbiome of our gut.
Like a garden, poor soil and unattended weeds can choke healthy plants, just like an unbalanced gut microbiome can harm the body. There are thought to be over 500 different species of bacteria in the GI tract, weighing over 1kg in the colon alone (9). So, it’s no surprise then that 70-80% of our immune system is expressed in the gut, and intolerances, allergies, asthma and eczema, depression and cancer can result from imbalances of these species (10). These conditions are often known as autoimmune diseases affecting our two distinct immune systems.
Our adaptive immune system, also known as our acquired or specific immune system, develops in response to specific pathogens that invade our bodies. After initially encountering pathogens, our white blood cells remember these invaders and can respond again if we reencounter them. This immunological memory is largely how we develop herd immunity, but errors can occur in this process, resulting in autoimmune diseases like multiple sclerosis (11).
There is no memory in innate immunity, it’s either on or off, and reacts to a broader category of pathogens rather than specifically targeting foreign invaders like the adaptive immune system. It’s comprised of physical barriers like our skin, body temperature, and internal pH. Innate immunity can be triggered, and is often over-activated, leading to an upregulation of background innate immune cells and function, resulting in autoimmune diseases like lupus (12).
We’re building a clearer picture here; there is a direct line between the health of our gut and our brains. An unbalanced gut microbiome leads to an overactive immune system, and an overactive immune system leads to inflammation.
Inflammation is the body’s immune response to injuries, pathogens, toxins, and foreign objects, and often results in redness, heat, swelling, and pain within the infected area. For instance, a burn on the skin will see the release of inflammatory cells to the damaged area to increase blood flow and water retention, clear necrotic tissue and begin repair (13). This short-term inflammation is why small injuries don’t prematurely knock us out of the evolutionary race. However, long-term or “chronic” inflammation can lead to autoimmune diseases like lupus, gout, diabetes, inflammatory bowel disease, and rheumatoid arthritis (14).
Both innate and adaptive autoimmune diseases result from chronic inflammation and can occur in conditions like being overweight and having a sedentary lifestyle, high blood pressure, cardiovascular disease, being diabetic and eating too many processed foods (You might notice this when you eat a McChicken burger and break out in pimples the next day) (15).
Scientists believe that chronic inflammation causes a build-up of misshapen proteins and amino acids, leading to a “loss of immune tolerance” and autoimmunity (16). These overactivated immune-inflammatory pathways are associated with mental illnesses like depression, anxiety, and chronic fatigue syndrome. Loss of immune tolerance is also linked to brain fog, depression, fatigue, and cognitive impairment in people with lupus and other autoimmune disorders (17).
All of us are prone to some level of inflammation, especially as we age and the level of baseline inflammation in our body’s rises. After all, we can tolerate alcohol more in our early 20’s than when we get older. Fortunately, there are many things we can do to lower the amount of day-to-day inflammation we experience.
To reiterate, there is a direct line between inflammation in our gut to the over-activation of our immune system and brain-related illnesses. Our goal then moving forward is to better regulate our immune responses, and we do this by encouraging the growth of a healthy gut microbiome and lowering inflammation in the body.
Of course, always consult your doctor to see if any of these changes are right for you.
Vitamin D is a hormone important for the brain and nervous system, immunity support and teeth and bone health. It maintains blood calcium levels by signalling to your intestines, bones and kidney to absorb, release, and retain calcium and phosphorus (18).
It’s also crucial for the diversity of the gut microbiome and can restrain an overactive immune system (19). Vitamin D helps to prevent the over-activation of the innate immune system, making a huge difference when differentiating between mild to severe outcomes of disease, i.e., whether people end up incredibly sick or dying from disease or have lingering issues. For instance, Low vitamin D has been linked to a higher risk of respiratory tract infections including COV-2 (20).
We can get enough vitamin D with as little as 10 minutes of sun a day and through foods such as fatty fish like salmon and tuna, eggs, mushrooms and cheese, as well as through supplementation (21).
The modern western diet contains large amounts of processed foods high in sugar and unhealthy fats, while also being low in important macronutrients. These foods which contain preservatives, artificial flavourings, high amounts of sugar and polyunsaturated fat are catastrophic for our gut microbiome. Stool samples of people eating highly processed food diets show higher counts of inflammatory markers and more often report feelings of mental fatigue and depression (22).
Simply decreasing the number of processed foods that you consume will go a long way in reducing inflammation in the body and improving gut health. That means eating foods lower in sugar, sweeteners like aspartame, preservatives, and trans and polyunsaturated fats. Here is a simple rule of thumb to consider when determining whether to eat packaged foods: if your grandmother doesn’t recognise the ingredients on the packet, don’t eat it.
Eat lots of fruits and vegetables, particularly leafy greens. These foods encourage a healthy gut microbiome as they are high in fibre which bacteria in your GI tract digest and use to grow. Consider eating spinach, broccoli, lentils, beans, green peas, blueberries, and bananas.
Research shows that consuming these foods can prevent the growth of harmful bacteria (23). Foods like pistachios and almonds in particular increase the number of good bacteria in the gut like bifidobacteria (24). And having high amounts of bifidobacteria has been shownto reduce inflammation in the intestines (25).
Probiotics are fermented foods like sauerkraut, kimchi, miso, and dairy products like cultured milk and yogurt, and prebiotics are foods such as rye, barley, tomatoes asparagus, onions, garlic, and artichokes. A study by Brain, Behaviour, and immunity found that consuming probiotics alleviated depressive symptoms by reducing inflammation in the gut (26).
It’s possible to overconsume these foods, leading to abdominal pain, bloating, and brain fog, so moderation is key.
Helminths are parasitic worms that coevolved with humans; they protect against inflammation and are often found in the GI tracts of healthy people. While we might not want to think of these crawlers creeping around inside of us, decreasing rates of helminth infection have been correlated with increased inflammatory and metabolic diseases like inflammatory bowel disease and diabetes (27). In fact, helminths have been found to safeguard against allergies and autoimmune diseases (28).
Talk with your doctor if you think helminths might be right for you.
The neurons in our gut just might be trying to tell us something; autoimmunity, GI issues, and even feelings of fatigue or brain fog might have more to do with the brain behind our belly button than the one on our shoulders. So, we want to support our immune system by lowing inflammation and encouraging the growth of good bacteria, and it mostly comes down to what we’re putting into our bodies, which brings new meaning to the term “brain food”.
Raise Your Spirit aims to help others live meaningful and happy lives, so we developed a Disability Performance and Wellness program called The RYS Acceleration SystemTM. This system is a practical at-home guide to help our clients determine the tasks, schedules, and key milestones to maximise their growth. By taking steps together, we hope to see a world where everyone feels great about themselves and their lives.
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