The Gut / Brain Connection

Have you ever had a ”gut wrenching experience?” Have you felt butterflies in your stomach, or had a “gut feeling?” We all have experienced the influence that our thoughts and feelings can have on our stomach, but research is now showing that our guts can influence our mood, behaviour and thinking more that we had previously realized.

The stomach and intestines are so rich in nerves that the gut’s nervous system, the enteric nervous system, has been called the “second brain.” Surprisingly, there are about 100 million nerve cells in the gut, as many as there are in the head of a cat. Nervous stress can affect digestion from a number of angles including reducing blood flow to the digestive organs, altering secretion of digestive juices, changing gut motility, increasing the leakiness of the intestine and, most importantly, altering the intestinal bacterial lining called the microbiome.

The enteric nervous system also informs our state of mind. “A big part of our emotions are probably influenced by the nerves in our gut,” says Dr. Emeran Mayer, a professor from U.C.L.A. It turns out that the main cranial (brain) nerve for controlling the digestion, the vagus nerve, uses 90% of its fibers to send information from the intestines to the brain. Electrical stimulation of the vagus nerve, a useful treatment for depression, may mimic these signals. The enteric nervous system, like the brain, uses neurotransmitters like serotonin and dopamine. In fact, 95% of the body’s serotonin is found in the bowels. So is there a link between impaired digestive function and mental or emotional disorders? The link is clear in autism and research suggests a link in depression, schizophrenia and more conditions of the mind.

Exciting research has emerged on the role of the bacteria in our guts and how it affects the brain. I recently attended the annual national conference of the Canadian Association of Gastroenterologists. Exciting research was presented on what is considered the most important work being done in the field of biology today. The Human Microbiome Project is an international collaboration to map the DNA of the trillions of bacteria that live in the human body. These bacteria are a critical determinant of digestion function, immune function, prevention of autoimmune disease and, as it turns out, mood. Changes in the intestinal microbiome can have profound consequences on our physical and mental health.

For instance, people with Irritable Bowel Syndrome have different wiring in their gut-brain connection. It has long been established that people with IBS have an amplified perception of pain from the intestines. Research now shows that it is their altered intestinal microbiome that is responsible for messing with the nerve signals from the gut.

In animal models, alterations in microorganisms of the intestines have been show to influence brain function including memory and anxiety. Studies on mice show that changes to gut bacteria can actually affect behaviour. If you take the gut bacteria from bold mice and put it into shy mice, the shy mice become bold and vice versa. Mice treated with good bacteria (probiotics) exhibit less anxiety and show changes in the hippocampus of the brain. They have more brain growth factors necessary for learning and higher thinking.
Researchers have found that people with major depression have alterations in their small intestine microbiome. Namely, they show signs of Small Intestine Bacterial Overgrowth (SIBO). My patients with SIBO often have been told they have Irritable Bowel Syndrome and suffer from bloating, constipation or diarrhea, fatigue, fibromyalgia and more. A simple breath test can help diagnose SIBO; with a long term complex treatment regime, relief of both physical and mental symptoms can be achieved.

Antibiotics significantly alter the delicate and complex intestinal microbiome. Not only does this disturbance have an impact on digestion and the immune system, but it has also been shown to affect behaviour. Mice that are given antibiotics are more daring, having lost their natural instinct to hide from predators. Studies have shown that post antibiotic mice have impaired learning. Also, changes in the critical areas of the brain, the amygdale and hippocampus, have been demonstrated with antibiotic use. Since 30% of human newborns are exposed to antibiotics before they even go home from the hospital, and with many more children are given antibiotics in childhood, the implications for brain development and learning are disturbing.

Stress can also alter the microbiome, leaving us more vulnerable to bowel issues, inflammatory conditions and mental effects of these changes. When mice are separated from their mothers at a young age, their microbiome changes and they are more likely to develop inflammatory bowel issues later in life.

There are other digestive factors that have a ripple effect on the brain. Food allergies can activate immune cells called mast cells. These mast cells can release inflammatory chemicals that can have an impact on the brain causing mood, energy, and learning issues. For some people with celiac disease, the autoimmune response to gluten in common bread and pasta products can cause calcifications of brain tissue that can be devastating.

If you are suffering from both digestive issues and mood issues, there may be more of a link that you had previously thought. Treating the digestive issues by correcting the underlying cause may open up doors to improved mood and mental clarity. Naturopathic physicians have a long history of working with patients to enhance the digestive system, through optimal diet, avoidance of food allergies, enhancement of the intestinal microbiome and much more. Don’t let your guts get you down. Take charge of your mental and physical health.

Dr. Deidre Macdonald is a naturopathic physician who has practiced medicine in downtown Courtenay for 16 years. For more information, contact her office at (250) 897-0235 or via this website.