The Gut-Brain Connection

Many of us have experienced the interconnected relationship that the gut and brain have on each other. The most common example is during times of anxiety, such as prior to public speaking, which causes stomach upset, pain, changes in appetite and changes in bowel habits because of stimuli originating in the brain. What we are not always aware of, is that this connection is not only from the brain to the gut, it goes both ways. An example of gut health impacting mental health, is that when an inflammatory meal that causes poor digestion and may even damage the gut wall, we can experience low mood, fatigue or even hyperactivity and poor concentration. Below are some symptoms that may be experienced with changes to either of these systems, but of course these lists are not exhaustive and vary from person to person.

Mental health changes that may be experienced with, or influenced by, altered gut health:

• Anxiety

• Irritability

• Low mood or depression

• Mood swings

• Poor mental focus or concentration 

• Poor memory or brain fog

• Low motivation

• Worsening symptoms in ADHD, ADD, autism, PTSD

Digestive changes that may be experienced with, or influenced by, altered mental health

• Constipation

• Diarrhea

• Nausea, vomiting

• Gas, bloating, abdominal upset or pain

• Belching, acid reflux, heartburn

• Other symptoms of poor nutrient absorption: fatigue, weakness

• Worsening of symptoms in IBS, IBD, food sensitivities, GERD, haemorrhoids 

How this communication takes place:

The gut and brain have been shown to communicate through a variety of forms. The main forms of communication that will be summarized in this article are: hormones, cytokines (inflammatory markers), neurotransmitters, nerve connections and metabolites. Let’s get into each: 

Hormones

Both the brain and gut have receptors for various hormones that exist throughout the body. 
Stress hormones (cortisol, epinephrine and norepinephrine) are produced mainly by our adrenal glad when stimulated by signals from the brain. These hormones influence perceived stress levels in the brain and strongly influence digestion. Stress levels have also been shown to influence the microbiome and vice a versa. The microbiome has been shown to play a role in stress-induced depression and anxiety, supporting the microbiome health has been shown to reduce cortisol output and reports of daily stress. High stress levels have been shown to alter the microbiome, which influences digestion, food sensitivities, and functions of the gut that impact other areas of body health. 

Sex hormones (estrogen, progesterone, testosterone) are hormones primarily produced by reproductive organs that are influenced by mental and gut health. Research is discovering sex hormone receptors located all throughout the body, which is no wonder why fluctuating hormone levels cause symptoms that influence many organs and body processed. The brain and gut are no exceptions, to better understand changes in mental and digestive health with each sex hormone, click here to read an article outlining this influence. 

Hunger regulating hormones, leptin & ghrelin, influence feelings of satiety and hunger respectively. Ghrelin is the hormones from the gut that tells the brain when we are hungry.  Leptin is produced by fat cells that tells the brain when we are full and have adequate energy stores from our food. In overweight individuals, it is thought that there is leptin insensitivity, meaning there is high levels of leptin circulating in the blood, but poor satiety singling. This can make weight loss very difficult if not addressed. 

Did you know that functional medicine testing is available to get a whole body understanding of circulating cortisol, epinephrine, norepinephrine, estrogen, progesterone and testosterone levels? Email or talk to Dr. Amber to learn more about functional medicine testing options available to you.

Cytokines, Gut Inflammation & Neuro-inflammation

Cytokines are proteins released by immune cells to regulate inflammation and the immune response. The gut is a massive producer of immune cells because it interacts and protects us from food, pathogens and toxins that exist in and on food. When the immune system in the gut is activated by a food sensitivity, the presence of a pathogen or toxin, the gut begins an inflammatory cascade of immune defence cells and cytokines to protect the body. These cells have been shown to not only cause inflammation and damage to the gut through this process, causing many digestive symptoms, but they also travel to various locations throughout the body causing inflammation outside of the gut. In individuals with gut inflammation, we see this also present in the brain as neuro-inflammation with symptoms like brain fog, poor concentration, poor memory, low mood, low motivation. This happens when inflammatory cytokines from the gut travel via the blood causing neuro-inflammation and interfere with neurotransmitter production. A correlation has also been documented between mental health conditions like depression and perpetuated inflammation. In these cases, it has also been shown that treating the inflammation improves both gut symptoms and mental health symptoms. 

So what can naturopathic medicine do for you? Comprehensive stool testing can help identify if inflammation is present and what is causing that inflammation: pathogens, microbiome disruption, poor digestion or immune response dysregulation. Stress levels and toxin exposure are also important testing options to consider the root cause of gut and neuro-inflammation. 

Neurotransmitters

Neurotransmitters include chemicals like serotonin, dopamine, GABA, epinephrine; which we are finding have important actions in the brain and the gut. 

Serotonin is known as the “happy” neurotransmitter, we are finding that large portions of serotonin (some have documented 80-95% of the body’s serotonin!) is produced in the gut, travels to the brain and influences mood and mental health. If digestion is not functioning properly, there is microbiome dysbiosis, there is gut inflammation or damage to the gut wall, less serotonin is able to be produced and mood can decline. And that is not all, serotonin also acts locally on the gut regulating digestion and preventing constipation. 

Dopamine’s activity in the brain has made it known as the “pleasure” neurotransmitter. Dopamine is released and allows us to feel accomplished and successful in the face of achievement and reward. Dopamine also influences the gut, regulating muscle movement, meaning it contributes to movement of food through the gut. When dopamine is low, we see sluggish bowels causing constipation. Dopamine is known to play a role in addiction; when it comes to food, research has shown that addictive foods; namely sugar, increases the release of dopamine contributing to a pleasurable feeling. Regulating dopamine may play an important role in managing food addiction and cravings.

GABA is another neurotransmitter found to have receptors and contribute to functioning in both the brain and the gut. In the brain, GABA is known to promote relaxation and a calm mind, when GABA is low we see anxiety, fear, poor stress tolerance, poor sleep. In the gut, GABA plays a calming role as well, promoting healthy flow of digestion. When GABA is low, we see changes in bowel habits, IBS and acid reflux. 

Epinephrine, also known as adrenaline, is released during times of stress (physical, mental, emotional, chemical). When the brain experiences stress chronically, and epinephrine levels are high, the gut slows digestion trying to absorb as much nutrition as possible, which can lead to constipation. 

As mentioned above, functional medicine testing provides options to get whole body levels of circulating neurotransmitters including serotonin, dopamine, GABA, epinephrine and their precursors to identify what may be causing changes in levels and how we can correct it. 

Nerve Connections

There are many sensory neurons in the gut that influence, and are influenced by, the neurons in the brain. The vagus nerve is one of the biggest nerves that connects the gut and the brain, and it is considered a modulator and communication line between the two. The vagus nerve plays a role in the parasympathetic nervous system, which is known as the “rest and digest” activity. If the parasympathetic nervous system is not activated, the body is predominated by the sympathetic nervous system, which is known as the “fight or flight” response. In short, the parasympathetic nervous system contributes to relaxation and rest, meaning its activation regulates healthy flow of digestion and bowel movements in the gut, and activation in the brain promotes calmness, prevents anxiety and depression. 

Activities with deep breathing, including meditation and yoga, are thought to benefit mood and manage anxiety through activation of the vagus nerve and parasympathetic nervous system. 

Metabolites & The Microbiome

When food is broken down (metabolized) in the gut to be absorbed by the body, the components created are known as metabolites. The gut microbiome plays an important role in metabolism, breaking down food and releasing metabolites to be absorbed and utilized by the body. When there is dysbiotic (an unbalanced) microbiome, this metabolism is not functioning properly and influences both digestion and neurochemistry. When certain gut bacteria are overgrown or deficient, food and waste metabolism changes. If there are not enough healthy gut bacteria, food is not broken down to be absorbed and so it ferments in the gut cause gas, bloating and changes in bowel habits. This can cause changes to nutrition status, which can influence energy and mood through changes in hormones and neurotransmitters as outlined above. If we do not have the necessary metabolites to make neurotransmitters and hormones there will be a deficiency. The microbiome’s connection to gut function and mental health is much more complex than this outline explains alone. 

When necessary, testing can be performed to better understand how the microbiome is functioning and how this may impact symptoms throughout the body. 

Summary
To close out this article, there is a tight connection between the gut and the brain. It is important to understand that when a naturopath is treating function in one of these areas, they will often treat both, and this is the reason you may come in with anxiety and have your digestion and gut health addressed first! If you are experiencing symptoms of changes in gut health or mental health, work with a naturopath to better understand how your symptoms relate so that together you can explore the need for testing and develop a personalized treatment plan. 

If you live in Alberta and would like to work together, click here to learn more about my practice and how to book an appointment.