Understanding the Gut-Brain Connection | Physician's Choice

Understanding the Gut-Brain Connection

December 28, 2020 8 min read

Hand holding gut-healthy greens

The gut-brain connection has been subject to an explosion of research and interest over the last several years. By now, many of us are aware that such a connection exists. 

But how exactly are the gut and the brain connected, how do they communicate, and what does it mean for your overall well-being? 

The gut and the brain communicate and influence each other in a number of different ways. The term gut-brain axis, or GBA, is often used to refer to the complex network that links the two organs. This network consists of physical and chemical connections that unite to create bidirectional communication, influencing many different aspects of health. 

There are several ways in which the gut and brain communicate. These include the enteric nervous system (ENS) or “second brain,” a sophisticated nervous system within the gut; the long and complex vagus nerve that stretches between the two organs; communication between the microbiome and the brain; and the influence of the gut on the immune system.

Gut bacteria produce neurotransmitters and other brain chemicals, regulate inflammation throughout the body, and influence everything from emotions to mood to memory. Brain chemistry and psychological health, in turn, have the power to influence gut health. 

Gut imbalances may underlie several neurological conditions and gastrointestinal disorders that are often accompanied by symptoms of depression or anxiety. 

You can support your gut-brain axis by balancing the gut microbiome with the help of probiotic and prebiotic supplements, dietary and lifestyle modifications, and natural techniques to improve vagus nerve function. 

Can we treat the brain by healing the gut? 

Mental health conditions, including anxiety and depression, have traditionally been considered psychological disorders. However, advances in research have helped us see most mental health conditions as multifactorial, in that a combination of different factors (including physiological imbalances) have contributed to their development. 

Anxiety anddepression, for example, have both been linked toinflammation throughout the body and imbalanceswithin the gut. Treating these underlying imbalances may, then, help to treat or resolve mental health conditions. This approach holds tremendous promise, especially given thefailure rates of standard antidepressants or other drug therapies. 

Healing the gut with holistic strategies is also appealing in that it targets what may be the root cause of an issue rather than merely treating its symptoms. 

Meet your second brain 

When we hear the word “neuron,” we naturally think of the brain. The brain is home to roughly 100 billion neurons or nerve cells responsible for sending and receiving information throughout the brain and body. 

The gut also contains approximately 500 million neurons, directlyconnected to the brain by nerves. This network of neurons makes up the gut’s own nervous system known as the enteric nervous system (ENS), sometimes referred to as the “second brain.” 

It’s hypothesized that the enteric nervous system originally evolved so the gut could independently control physical processes related todigestion. However, the ENS is capable of so much more than digestion. 

The feeling of butterflies in your stomach—familiar to virtually all of us—is one commonly cited example to illustrate how our emotions and state of mind are tied to signals from the gut. Research suggests, though, that this feeling is only the tip of the iceberg when it comes to communication between the “second brain” and the one above our shoulders. 

The vagus nerve

The longest and most intricate of the nerves connecting the brain and gut is called the vagus nerve. Thevagus nerve can be thought of as the roadmap in a series of highways. It runs in both directions, facilitating communication between the two organs. 

The vagus nerve is considered a pivotal component of thegut-brain axis and has been the subject of a significant amount of recent research into the gut-brain connection. 

The activity of the vagus nerve is referred to as “vagal tone.” Because of the role this nerve plays in the parasympathetic nervous system (sometimes referred to as the “rest and digest” system), vagal tone can be roughly measured by simultaneously tracking an individual’s heart rate and breathing rate. 

Individuals with somedigestive disorders, including Inflammatory Bowel Syndrome (IBS) and Crohn’s disease, as well as those with mental health conditions including depression, have exhibited reduced vagus nerve activity or vagal tone. 

Stimulating the vagus nerve with the help of a pacemaker-like device has been found to relieve symptoms of depression,PTSD, anxiety, and Inflammatory Bowel Disease.

Fruit on a tree with gut-healthy fiber to support the gut-brain connection

The influence of the gut microbiome

Understanding the gut microbiome is essential for understanding the gut-brain connection. 

Thegut microbiome has an enormous influence on both physical and psychological health. Microbes in the body play crucial roles in digestion, metabolism,immune system function, learning, memory, emotional regulation, stress management, mood, and pain perception. 

Although researchers are still learning what exactly makes up a healthy gut microbiome, they’ve identified several helpful (and harmful) bacteria strains. Diversity is also important, and researchers have zeroed in on beneficial interactions among certainstrains of bacteria

Changing brain chemistry by changing gut bacteria

Changing the composition of the gut microbiome, whether through the use of probiotics, antibiotics, or fecal transplants, can fundamentally alter brain chemistry. 

One animal study found that antibiotics—known to disrupt the microbiome—caused a dramatic shift in behavior, leading a once-timid group of mice to become suddenly fearless and bold. Changes in the levels of certain brain chemicals were also observed. 

In afollow-up study, researchers colonized two different breeds of mice with bacteria from one another. The mice known for being timid again became bolder, while those known for being fearless were now cautious and shy. 

Studies like these are fascinating for what they suggest about the role of gut microbes in what we consider to be intrinsic personality traits. 

Researchers have identified significant differences between thegut microbiomes of those with conditions like anxiety and depression compared to those without them. In one such study on patients with Major Depressive Disorder, researchers were able to zero in on a specific bacterial strain, the levels of which were associated with the severity of depressive symptoms. 

In human trials,probiotics have been shown to decreaseanxiety and depression in healthy individuals, those with diagnosed mental health conditions, and IBS patients with symptoms of depression.

Studies using fMRI technology for imaging have also demonstrated that probiotics can altercognition and activity in brain regions associated with emotional processing. 

Gut bacteria and neurotransmitters

Neurotransmitters are chemical messengers that influence mood, cognition, and emotions. 

Humans produce more than 40 different kinds of neurotransmitters, each with their own unique functions and effects. Some of the most important and well-known neurotransmitters are serotonin, dopamine, and norepinephrine. 

Interestingly, these chemicals are not only produced in the brain: Cells and bacteria in the gut are also responsible for neurotransmitter production. In fact, more than 90% ofserotonin (the mood-regulating neurotransmitter) is made in the microbiome. 

Gut bacteria are also responsible for the production ofGABA, a neurotransmitter involved in managing feelings of anxiety. 

In addition to neurotransmitters, your beneficialgut microbes are responsible for producingother chemicals, including short-chain fatty acids (SCFAs) that are essential for both brain and gut health. 

The immune system connection

The immune system also plays a role in the gut-brain connection. 

A healthy gut is an essential component of a healthy immune system. Issues in the gut, including increasedintestinal permeability (leaky gut) anddysbiosis (an imbalance between beneficial and harmful bacteria), can impair immune system function. This can lead to chronicinflammation throughout the body as the immune system reacts to excessive stimuli. 

Many conditions traditionally thought of asbrain disorders, including depression and Alzheimer’s disease, have been linked to systemic inflammation. Given the role the gut plays in regulating immune function and inflammation, this is a vital component of the gut-brain connection. 

This connection may also explain the tendency for mental health conditions like anxiety and depression to accompany chronic, inflammatory gastrointestinal disorders likeIBS and IBD. 

How the brain influences the gut

Research has primarily focused on the influence of the gut on the brain. But the communication between these two organs goes both ways, and brain chemistry can influence the gut microbiome as well. 

Psychological stress, for example, has been shown to negatively impact the gut microbiome, reducing the levels of beneficial bacteria strains. This can catalyze a vicious cycle, as imbalances within the gut microbiome may lead to further stress on the gut-brain axis and exacerbate the problem. 

Probiotics for gut and brain health

Given the profound influence of the gut microbiome on mental health, many experts have turned to probiotics as a potential treatment option or preventive measure for mental health conditions. 

Probiotics are beneficial strains of live bacteria that you can get from supplements orfermented foods. Some strains are particularly beneficial for the gut-brain axis, often referred to as “psychobiotics.” 

Studies have shown thatprobiotics can improve symptoms ofdepression andanxiety, along with stress and other conditions like Chronic Fatigue Syndrome. 

Research has shown that probiotics can also offerpsychological benefits to generally healthy individuals. 

Some of the most helpful strains includeBifidobacterium longum, Lactobacillus acidophilus, Lactobacillus casei,andBifidobacterium bifidum

Prebiotics—fibers that serve as food for beneficial bacteria—have also been shown to help with anxiety andstress alone and in combination with probiotic supplements. 

Woman with arms outstretched near the ocean for stress relief

How to support the gut-brain axis

Beyond probiotics, there are many simple things you can do to support your gut-brain axis:

  • Addfermented foods to your diet. Fermented foods like yogurt and sauerkraut contain live, beneficial bacteria (probiotics) and can help support the health of the gut and the brain.

  • Eat plenty of foods high in prebiotics.Prebiotic fibers help feed the good bacteria in thegut and improve brain health. Garlic, onions, leeks, yams, barley, oats, and asparagus are a few examples of prebiotic-containing foods.

  • Consume lots ofomega-3 rich fats. These healthy fats help boost levels of beneficialgut bacteria, reduce inflammation, and supportcognitive function. Good sources of omega-3 fats include salmon, walnuts, flaxseeds, and cod liver oil.

  • Increase your intake of polyphenols. Polyphenols are plant chemicals that help increase beneficial bacteria in the gut. Good sources includedark chocolate, berries, broccoli, olive oil, and green tea. A healthy Mediterranean diet, high in both omega-3 fats and polyphenols, has positively impacted gut and brain health in a number ofstudies.

  • Stimulate thevagus nerve and improve vagal tone at home. Research has shown that techniques likemeditation, deep breathing, and yoga can stimulate the vagus nerve and improve the health and function of the gut-brain axis.

  • Avoid dysbiosis triggers. Refined and processed foods,sugar,stress, andantibiotics are among the factors that contribute to an imbalance between beneficial and harmful bacteria in the gut. 

In summary

The gut-brain connection has been the focus of a great deal of research and media attention in recent years. The gut and the brain are linked in several different ways and remain in constant communication. 

The gut-brain axis, which refers to the complex network linking the two organs, consists of both physical and chemical connections. 

The gut is home to its own nervous system, the enteric nervous system (ENS) or “second brain,” which houses some 100 billion neurons. Several nerves, including the powerful vagus nerve, connect this nervous system to the brain and facilitate bidirectional communication. 

The gut microbiome affects the brain by producing neurotransmitters like serotonin, modulating immune system function and inflammation, and influencing emotions and cognition. Similarly, imbalances in the brain also influence the makeup of the gut microbiome. 

Gut health issues may be at the root of many mental health conditions as well as neurological conditions. 

Healing the gut, in turn, can help to support the brain. We can support the health of this gut-brain connection with simple interventions, including the use of high-quality probiotic and prebiotic supplements, dietary and lifestyle changes, and natural vagus nerve stimulation.

Ellie Ellias -Contributing Writer, Physician’s Choice 

Up next: Understanding the Gut-Hormone Connection

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