Butterflies in your stomach, gut feelings, a fire in the belly: There is no shortage of expressions connecting the gastrointestinal system to our emotions. But did you know that science backs up these expressive turns of phrase? The gut-brain axis, also known as the gut-brain connection, is a real phenomenon with connections to various conditions, including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and anxiety.
We spoke with Dr. Eamonn Quigley, a gastroenterologist at Houston Methodist, about the gut-brain axis, and its implications for our health.
What is the gut-brain axis?
Dr. Quigley says the concept of the gut-brain axis or gut-brain connection has evolved as a way of explaining how the brain and the gut interact in terms of developing various symptoms, such as abdominal pain, nausea, vomiting, bloating and more.
"The gut has sensory nerves, and they transmit messages through the spinal cord, through the vagus nerve, to the brain, where then they're recognized and if the brain decides so, acted upon by the brain sending signals down to the gut leading to changes in gut motility or secretion," Dr. Quigley says.
"In some situations, it can be the brain predominantly influencing the gut," he says. "In other situations, it can be the gut influencing the brain."
Dr. Quigley says that stress is a good example of the concept.
"When you're stressed, you may get diarrhea, you may feel nauseated and that is the brain obviously acting directly on the gut and affecting its motility, etc.," Dr. Quigley says. "But of course, the opposite may happen as well, and symptoms originating from the gut are felt in the brain and lead to pain, nausea, bloating, etc."
You can see this in action with conditions such as IBS or chronic gut pain, where people with these issues can develop anxiety or may become depressed. When this happens, their gut symptoms get worse which makes them more anxious and a self-repeating vicious cycle is set up.
The gut microbiome, the microscopic ecosystem made up of bacteria, fungi and microorganisms, plays a crucial role in our digestion, metabolism and immune system, and is now seen to be a component of the gut-brain axis. In fact, the gut microbiome is in constant communication with the brain through an information relay that works both ways — the microbiome gut-brain axis.
The gut-brain axis influences many of the body's functions
In addition to our stress levels and mood, the gut-brain connection impacts a good number of bodily functions. Many are related to the gut, including digestion, gut motility (the muscle contractions that power digestion), metabolism, hunger and even food cravings. This connection can also affect our immunity, behavior, cognitive function and even our pain tolerance.
"Pain of virtually any origin will have a gut-brain element to it, whether it's fibromyalgia or chronic fatigue," Dr. Quigley says. "Most anything you can think of — whether it's cardiac symptoms, respiratory symptoms — to a greater or lesser extent will have a gut-brain element. It's a pretty universal paradigm, and it's very important to understand and appreciate its role."
Conditions linked to the gut-brain axis
Virtually every GI condition, to a greater or lesser extent, will have some gut-brain element, according to Dr. Quigley. Two of the most commonly affected are IBS and IBD, including Crohn's disease and ulcerative colitis.
RELATED: IBS vs. IBD: What's the Difference?
"In irritable bowel syndrome, you can have a variable role of the gut-brain axis," Dr. Quigley says. "For example, in some people, the symptoms primarily arise from the gut. They may be modified a little bit by the brain, but they primarily originate from the gut. In other people, particularly people with more severe IBS who also have anxiety, depression or somatization [psychological distress caused by symptoms of unknown origin], the symptoms may be primarily driven by brain input, but obviously they're expressed in the gut."
Dr. Quigley says that the main goal of therapy with IBD, including Crohn's and ulcerative colitis, is to suppress or eliminate the inflammation that causes symptoms.
"There is a gut-brain connection with IBD in that sufferers, as a result of inflammation, may become depressed or anxious," Dr. Quigley says. "If they are stressed, it may exacerbate their inflammatory bowel disease because input from the brain can directly affect inflammation in the gut."
Other conditions related to the gut-brain axis can include noncardiac chest pain, anxiety and depression, and disorders such as Parkinson's disease or multiple sclerosis.
What treatments can help with conditions affected by the gut-brain axis?
With both IBS and IBD strongly associated with the gut-brain axis, Dr. Quigley says that there are a variety of what gastroenterologists call mind-gut interventions to help ease some of the symptoms brought on by the brain-to-gut connection.
"Mind-gut interventions are extremely beneficial, and they can go all the way from medications like antidepressants or antianxiety drugs, usually used in very low doses, to behavioral therapies," Dr. Quigley says. "In this context antidepressants and antianxiety drugs are not really being used in terms of their antidepressant or antianxiety effects, but they seem to have an effect on the sensory input from the gut.
"Behavioral or mind-body therapies, like cognitive behavioral therapy, hypnotherapy and mindfulness therapy have all been shown to be effective in patients with irritable bowel syndrome, and particularly in those who have a significant brain-to-gut component of it."
Can over-the-counter vagus nerve stimulators ease GI symptoms?
The vagus nerve, the longest of the cranial nerves, is crucial for the brain to communicate with the rest of the body and vice versa. Vagus nerve stimulation is a treatment that sends electrical pulses through the vagus nerve to your brain stem. Surgically implanted vagus nerve stimulator devices were approved by the U.S. Food and Drug Administration in 1997 and have been used to treat drug-resistant epilepsy and other conditions.
Now, noninvasive, wearable over-the-counter vagus nerve stimulators are being marketed as being able to help with everything from lowering stress, easing IBS symptoms and being a drug-free option for treating depression.
"What is less appreciated is that the vagus nerve is actually predominantly a sensory nerve, that most of the fibers in the nerve actually deal with sensation, not with sending messages down, but sending messages up," Dr. Quigley says. "The vagus is a crucial component of the gut-brain axis in the generation of vasovagal reflexes.
"An example is when you eat a meal and your stomach becomes full, sensory nerves in the vagus send a message to your brain to say your stomach is too full, you need to stop eating, and that is turned around through a reflex down into the stomach to relax the stomach and allow you to eat some more. That's called gastric accommodation, which is a vasovagal reflex and there are lots of those."
Dr. Quigley says that there is some evidence that vagus nerve stimulators can help modify gut sensation, but they're not being widely used for that reason yet.
The over-the-counter devices can come with a high price tag. Without clinical guidance, you may be paying for a placebo effect. That said, if you're still interested, these wearable devices' risk is low.
Can using probiotics improve the gut-brain axis and your mental health?
The concept of the microbiome gut-brain axis acknowledges that the microbes in the gut can signal to the brain and that the brain can, in turn, impact the composition of the microbiome.
RELATED: PODCAST: What Are Probiotics & Who Should Take Them?
"It's a relatively new concept, but one that seems to have quite a deal of experimental evidence," Dr. Quigley says. "There is data, including some research we did at Houston Methodist, to show that by modulating the microbiome with a probiotic, for example, you can influence symptoms like depression and anxiety. It's not an awful lot of data, but at least there is some data out there to suggest that you can modulate brain symptoms or brain-originated symptoms by giving probiotics into the gut."
Why the gut-brain axis is important — and how you can support its function
A healthy gut-brain axis is crucial for our overall health because when it functions optimally, we are blissfully unaware of the many signals going back and forth between the gut and the brain, orchestrating our entire digestion process.
"If we were aware of these signals, we'd have pain, bloating and nausea all the time," Dr. Quigley says. "So the ability for that traffic to occur at a subconscious level is very important for normal functioning of the GI tract and for people to be healthy and symptom-free. Obviously, when that goes awry, you begin to feel it."
In fact, Dr. Quigley states that people with irritable bowel syndrome or related symptoms are more aware of the everyday activity within the gut that other individuals are blissfully unaware of.
"They're more aware of motility in the gut, and they're even more aware of motility in the gallbladder," Dr. Quigley says. "So, they have symptoms where most people would not have any symptoms whatsoever."
While Dr. Quigley says that there is no single prescription for maintaining or improving your GI function, he emphasizes the importance of maintaining a healthy weight and following a diet such as the Mediterranean diet for sustaining a good microbiome and colonic function. The Mediterranean diet is rich in fruits, vegetables, whole grains and plant-based proteins, such as legumes, which are high in fiber content. Eating enough fiber and staying hydrated are both crucial factors in maintaining healthy GI function.
Additionally, there are things we should avoid if looking to improve our GI health. Smoking is tied to a number of GI conditions, including Crohn's disease and certain GI cancers.
"The general lifetime measures that we say are good for our overall health also apply to our gut health," Dr. Quigley says.
