The butterflies you felt in your stomach as you were about to take an exam, speak in public, or give a big work presentation were not a figment of your imagination, but a sign of the interconnected relationship between your mind and your digestive system.
“There is a very intimate connection between the brain and gut,” says Jennifer Christie, MD, head of the Division of Gastroenterology and Hepatology at the University of Colorado Department of Medicine.
Understanding this connection is important because of the potential influence the brain has on many gastrointestinal disorders, such as functional bowel disorders — otherwise known as disorders of the gut-brain axis. Christie explains that there are more than 20 disorders in this category, with common types being functional bloating, constipation, diarrhea, and irritable bowel syndrome — a potentially debilitating disorder that affects an estimated 25-45 million people in the United States.
It can be difficult to get a diagnosis for these conditions because they can present as a variable combination of chronic or recurrent gastrointestinal symptoms that cannot be explained by intestinal blockage, inflammation, or lab abnormalities.
“It can be very frustrating for patients who experience symptoms, yet their tests don’t reveal abnormalities. Functional bowel disorders are a group of diagnoses that are fairly common; however, we’re still trying to understand why this happens,” Christie says. “We do know that these symptoms, oftentimes, are related to signals firing between the brain and gut.”
Exploring the brain-gut relationship
Christie says the close connection between the brain and gut is largely related to the complex nervous system known as the enteric nervous system that exists in the gut and communicates with the brain (the central nervous system) via the autonomic nervous system.
The vagus nerve, which runs from the lower part of the brain to the stomach, helps transfer information in a bidirectional manner. This nerve functions within the autonomic nervous system and allows for this communication between the brain and gut.
“The enteric nervous system is embedded within the autonomic nervous system and drives motor function and sensations we feel in our gut,” she says. “There are hormones, like serotonin, and other chemicals that help transfer and receive information about motor function and sensation.”
Understanding how the signaling between the brain and gut works — and how it can influence functional bowel disorders — is complicated, as researchers do not have all the answers.
“The way in which these functional bowel disorders develop is multifactorial. Specific signals between the brain and gut axis can trigger certain intestinal functions and, therefore, symptoms,” Christie says. “Why does that happen? There may be several reasons, and from a biochemical standpoint, we think serotonin is the main gut hormone that is modulating the disconnect; however, there are other hormones and neurotransmitters that contribute.”
Serotonin and the gut microbiome
Most people only think of serotonin as a brain hormone that affects symptoms of depression or anxiety, but many do not realize it also plays an important role in the gastrointestinal tract.
“The majority of the body’s serotonin is produced and stored in gut cells. Serotonin helps modulate how the gut moves — the contractions, what we call peristalsis, of the gut. It also affects how we perceive sensations in our stomach and intestine, such as hunger, feeling full, or sensations of air — bloating — or liquid in the gut,” Christie says.
Due to its important role, many medications used for patients who have irritable bowel syndrome with constipation or diarrhea target serotonin receptors in the gut.
However, targeting serotonin is only a piece of the puzzle. The way functional bowel disorders develop involves many other factors — some of which may not be known as of yet, Christie cautions. Some of those contributing factors may include how the body responds to environmental exposures, food triggers, a person’s genetics, and the gut microbiome, which is the ecosystem of bacteria, viruses, and fungi that naturally live in a person’s intestinal tract.
“The gut microbiome produces chemicals and hormones that may trigger how our gut feels and functions. These chemicals and hormones are translated to the brain, and the brain then confers that information back to the gut to maintain the microbiome,” she says. “It is a constant loop.”
Researchers across the globe, including those in the CU Division of Gastroenterology and Hepatology, are investigating the role of the microbiome and gastrointestinal disorders.
“There is a lot that is still unknown. For example, are people programmed to establish a microbiome environment that would put them at risk for some of these symptoms of functional bowel disorders? And can we modify this in a way that is sustainable and relieves symptoms?” Christie says.
What you can do to support your brain and gut health
There is an array of therapies to help patients with functional bowel disorders, depending on a person’s symptoms. Importantly, given how the brain can affect the gut, there are behavioral therapies that can also be effective in helping to relieve symptoms.
“Providers like myself who take care of these patients may refer patients for biofeedback, cognitive behavioral therapy, gut-directed hypnotherapy, and other psychological therapies to help modulate the body’s response to external triggers. This can help change a patient’s thinking so that a physical response does not cause gut symptoms such as pain, diarrhea, constipation, and even nausea. Each of these symptoms can become quite debilitating,” Christie says.
One of the most important steps a patient can take is to listen to their body, she notes, saying: “It’s true — the gut instinct is real. You have to listen and avoid those things that trigger you, whether it be avoiding certain foods or drinks, or even certain behaviors.”
Other strategies that people can use to support their gut health — regardless if they have functional bowel disorders or not — include getting adequate sleep, exercise, and managing stress levels.
“We know that even simple day-to-day stress can impact our gut function and what we feel in our gut. It’s so important to try to recognize these triggers and develop strategies to manage them. Often, we may need help from healthcare providers to do this,” she says. “An action that you can take is to integrate a regular exercise routine into your week. This supports your mental and physical health as well as helps to regulate the impact of stress on your gut function.”
There is still much for researchers and health care providers to learn about how the brain affects the gut, and vice versa, including determining who is at risk for these disorders, what are the pathways that trigger these issues, and other methods of intervening to reduce symptoms.
“Some of that work is being done here at CU, and we have a fantastic team of providers who can advise patients on the best approach to support their health,” Christie says. “If you are experiencing symptoms, talk to your health care provider early to be able to get advice and the appropriate recommendations you need to improve your overall gut health.”
