What Is the Gut–Brain Axis?

Intestinal health is quickly becoming one of the most critical components in maintaining optimal well-being, including mental/emotional as well as physical. In recent years, it has become more common to refer to the gut as our “second brain,” meaning it can engage in neurological activity independently from the central nervous system. At any given moment, the brain and the gut are in complex, essential communication, giving rise to a two-way flow of information called the gut–brain axis.

The “second brain” — in technical parlance, the enteric nervous system (ENS) — controls the gastrointestinal (GI) system and is linked to the brain by millions of neurons. While our ENS is in constant contact with the central nervous system, it can also act independently, performing the important role of monitoring the entire digestive tract without direct supervision from the brain.

The ENS is made up of two thin layers with more than 100 million neurons in them — more than the spinal cord. These cells line the gastrointestinal tract, controlling blood flow and secretions to help the GI tract digest food. They also help us “feel” what’s happening inside the gut, since this second brain is behind the mechanics of food digestion.

While the second brain doesn’t get involved in thought processes like political debates or theological reflection, it does control behavior on its own. Researchers believe this came about to make digestion more efficient in the body; instead of having to “direct” digestion through the spinal cord and into the brain and back, we developed an on-site brain that could handle things closer to the source.

The gut and brain are also connected through chemicals called neurotransmitters. Those produced in the brain control feelings and emotions. The best known of these is serotonin, which contributes to feelings of well-being. Another very important one is gamma-aminobutyric acid (GABA), which helps control feelings of fear and anxiety and helps with sleep regulation. A large proportion of serotonin, GABA, and other neurotransmitters are produced by gut cells and the trillions of microbes living in the GI tract. 

It used to be thought that neurological disorders such as depression and anxiety trigger autoimmune conditions such as irritable bowel syndrome or other digestive-related issues. However, the opposite is likely true — in other words, dysfunction in the gut may in fact cause changes in mood and behavior, triggered by the enteric nervous system. An estimated 30 to 40 percent of the population suffers from digestive-related illness, which helps explain why a higher-than-normal percentage of people with a compromised gut suffer from mood-related challenges such as depression and anxiety.

As our understanding of the gut–brain axis deepens, we are gaining a better appreciation for why taking good care of our gastrointestinal health can lead to significant improvements in our mental and emotional well-being.

What Can Disrupt the Gut–Brain Connection?

Stress has very deleterious effects on health, including the gut–brain axis. Our body’s immediate reaction to stress, whether physical or mental, is to release the hormone adrenaline and other “stress hormones” to help us survive. For instance, if you’re hiking and encounter a mountain lion, your body goes into survival mode. Your heart beats faster, your eyes widen, and even your blood platelets become sticky in case the dangerous encounter leaves you bleeding; your blood will clot more quickly. Once the stressful situation is over, your body stands down from the fight-or-flight response and returns to normal.

This is perfectly healthy. The problem arises when you’re living in a chronic state of stress — working in a stressful environment, for example. Since your body cannot differentiate between a physical stressor, like being pursued by a mountain lion, versus a mental stressor, like an unpleasant job, it reacts the same way and keeps on reacting. The prolonged presence of adrenaline and other stress-related hormones generates inflammation throughout your body.

Inflammation is the immune system’s natural response to toxins, infection, and stress. If inflammation is experienced over a prolonged period of time, the immune system weakens, leading to neurodegenerative diseases such as Alzheimer’s and Parkinson’s, as well as neurological disorders such as ADHD, autism, anxiety, and depression. Roughly 80 percent of the immune system is located in the gut, which makes gut health a primary concern to achieve optimal health.

Environmental toxins are substances that work in direct opposition to natural healing and can have a very negative effect on the gut–brain connection; they are numerous and include lead, mercury, cadmium, and arsenic. Environmental toxins can create a negative and potentially life-altering pattern in the brain and body (the “brain–body”) or worsen a negative pattern. They tell your brain to stop healing the body, and they can make you jittery and reactive. 

We carry these toxins in our fat tissues and release them with fat loss. Most of us also carry the most common environmental toxins in our bones, and every day — through our diet, the water we drink, the products we use — we take in a little more. Around age thirty-five, as bone buildup slows down and bone breakdown begins, the body slowly releases these substances into the bloodstream. The brain–body can become a little more poisoned each day from this internal storehouse of toxic substances, as well as new exposures, including in the food we eat — especially foods with pesticides, herbicides, genetically engineered ingredients, and hormones — the water we drink, the products we use, and the air we breathe.

Glyphosate is a weapon of mass destruction in our food supply that is ruining the gut–brain connection. It disrupts the integrity of the gut barrier and may then disrupt the integrity of the blood–brain barrier, leading to inflammation. Glyphosate is associated with increased anxiety, attention deficit, depression, weight gain, cancer, memory impairment, and other brain–body problems. Its residues are commonly found in GMO foods and conventional wine.

The Role of Microbes in the Gut–Brain Axis

 Gut health is determined by the collection of bacteria that resides in the GI tract, commonly referred to as the microbiome. The key to optimal gut health is maintaining a healthy diversity and balance of good and bad bacteria in the microbiome.

The microbiome plays a crucial role in the immune system and in brain function. The overgrowth of bad bacteria can cause many complications, such as dysbiosis (microbial imbalance) and bacterial overgrowth in the gut. These eventually lead to more serious conditions, including inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis, as well as neurological issues such as depression and anxiety.

The trillions of microbes in the gut make numerous chemicals that affect the brain. Certain gut bacteria make a compound called brain-derived neurotropic factor, which helps the brain stay young and build new pathways. A healthy brain requires the right level of hormones to stay sharp, and the right neurotransmitters to focus, and the microbiome makes vital contributions in both respects. Gut microbes also produce abundant short-chain fatty acids (SCFAs), such as butyrate, propionate, and acetate, by digesting fiber. SCFAs affect brain function in a number of ways, such as by reducing appetite. Finally, gut microbes metabolize bile acids and amino acids to produce other chemicals that affect the brain.

As such a large proportion of the immune system is located in the gut, the microbiome plays a key role in that system’s functioning by controlling what is passed into the body and what is excreted. When the microbiome isn’t healthy, inflammation results, which is associated with a number of brain disorders, including depression, anxiety, Alzheimer’s, dementia, and schizophrenia.

Clearly, if we want to repair breakdowns in the gut–brain axis, we need to focus on the microbiome. There is now extensive research being executed to explore how the microbiome can be utilized to fight illness and disease.

Ways to Repair the Gut–Brain Connection

Probiotics are supplements containing specific strains of bacteria that contribute to maintaining a healthy microbiome in the gut. Studies show that taking probiotics can reduce feelings of depression and anxiety and improved overall well-being.

A recent study looked at how the gut and brain are connected by examining the effects of probiotics on patients with irritable bowel syndrome and depression. The researchers found that twice as many patients saw improvements from depression when they took the probiotic Bifidobacterium longum NCC3001 daily compared with patients who took a placebo. Studies in laboratory mice have shown that certain probiotics can increase the production of GABA and reduce anxiety and depression-like behavior.

Fermented foods contain various species of Lactobacillus and Bifidobacterium bacteria that can contribute positively to the microbiome. Examples include sauerkraut, kimchi, and kefir.

The good bacteria in the gut’s microbiome require appropriate food materials, and these are known as prebiotics. The best sources for prebiotics are: asparagus, bananas, carrots, chicory root, coconut meat & flour, dandelion greens, flax and chia seeds, garlic, Jerusalem artichoke, jicama, leeks, onions, radishes, tomatoes, yams.

Bone broth is one of the most healing and nourishing foods for the gut. It aids in reducing inflammation and helps provide the gut with the necessary nutrients for healing. Bone broth also contains collagen and cartilage, two proteins that help rebuild the gut lining, as well as glycine, proline, and l-glutamine — amino acids that are essential for repairing and rebuilding the body. L-glutamine promotes digestive health, brain function, and muscle integrity. It is an important nutrient in relation to the gut, because it helps repair and rebuild intestines and strengthen the gut lining.

You can also use your beliefs along with the basics of neuroscience to improve spiritual neuroplasticity and build a better, healthier brain-body connection. Something as simple as a walking meditation on a daily basis can lead to important changes. A daily practice can increase blood flow to the brain, grow the grey matter and create a connection to something greater. This has measurable effects on the brain that improve brain-body physiology and provide a shield against the normal stress of daily life.

Although the brain represents only 2–3 percent of the body’s total weight, it consumes 25 percent of the body’s glucose supply and 20 percent of its oxygen and cardiac output. The brain is the single biggest consumer of what we put into our bodies, yet most of us don’t consider our brains when making food choices, focusing instead on calories. We rarely think of how our brain is going to benefit or suffer from our food choices.

In reality, the food you consume has the potential to help or hurt your gut first, then your brain, and finally the rest of your body. Food is information not only for the DNA of your cells but also for the DNA of the microbes in your gut. The food on your fork determines your gene expression, hormone levels, immune activity — even the stress levels in your gut, your brain, and the rest of your body. A change in the food you eat rapidly alters the activity of the gut microbiota — typically within one to four days, and in some cases, within just six hours.

A healthy brain–body connection exists when your brain and your body are fully in sync and congruent in their mission and goals. Healing conversations are occurring. Your gut is having a healing conversation with your brain, and your heart is telling your brain’s overactive stress-response system that it can calm down. In short, having a healthy brain–body connection means that you don’t have the high levels of inflammation that cause brain–body breakdown.