Gut health and brain health. What is the connection?

Have you ever had to do a presentation or a big test and felt butterflies in your stomach? Have you wondered why the stress caused stomach pain? You can thank a little-known nervous system in your abdomen for that.

Most of us have heard of the central nervous system (CNS), which is made of your brain and spinal cord, but there is also another nervous system that you may not have heard of: the enteric nervous system (ENS). The ENS contains a hundred million nerve cells that line the gut, from the esophagus through the stomach and intestines, all the way to our rectum. And studies show a link between these two systems. The ENS and CNS send signals back and forth to affect our gut and brain health. As a result, disturbances in our gut can lead to problems with mood and cognition. And problems with our brains, such as mood disorders, can cause stomachaches.

“The ENS is like our second brain, working in tandem with the CNS,” says Dr. Mashal Batheja, an assistant professor of medicine in gastroenterology at the Mayo Clinic. “The ENS can also work independently of the CNS. The ENS helps determine how quickly food and water pass through the gut. The ENS also communicates with the millions of immune cells in our gut. It helps regulate the health of our digestive system.”

“The ENS tells the CNS when we are full and then we stop eating,” Batheja added. “And stress signals can be sent from the brain to the gut, sometimes resulting in pain.”

The ENS and CNS are connected by the vagus nerve, which sends signals back and forth between the brain and the gut. And both systems produce chemicals called neurotransmitters that send messages throughout your body that help it perform a variety of functions. Many people already know that the brain produces a neurotransmitter called serotonin, which gives people feelings of happiness, but what they may not realize is that 90% of the serotonin in our body is actually produced in the gut.

Another neurotransmitter called gamma-aminobutyric acid (GABA), which helps us control feelings of fear and anxiety, is also produced in the gut (as well as in the brain).

The role of the microbiome

According to Dr. Jay Pasricha, director of the Johns Hopkins Center for Neurogastroenterology, the microbiome is the balance between bacteria and other organisms in our gut and affects all aspects of human health and disease.

“The microbiome is involved in all aspects of human health and disease,” Pasricha said. “The microbiome influences the signals that our gut sends to the brain and other organs. It produces factors that stimulate the gut lining in ways to affect the brain.”

Why does the microbiome have such an impact on our overall well-being? According to Dr. Meredith Wicklund, a neurologist at Mayo Clinic: “The microbiome creates several metabolites and neurotransmitters like serotonin and GABA that send signals to the brain and affect how the brain functions. It affects mental health, and it’s bidirectional in that anxiety can change the makeup of the microbiome, and certain GI symptoms can lead to anxiety.”

Bacteria Lactobacillus in human gutiStock.com/nopparit

The intestines, functional disorders and your mood

While some of us just have mild abdominal pain during stressful times, others experience severe abdominal pain or gastrointestinal distress even when no structural problem can be identified on scans or through blood tests. These are called functional bowel problems and anywhere from 35% to 70% of us have them. An example of a functional bowel problem is irritable bowel syndrome (IBS), and this can be explained by the fact that people with IBS often have reduced vagus nerve function.

“Functional disorders such as IBS have no apparent structural cause and are associated with a high frequency of anxiety and depression,” Pasricha said.

“And it’s true that the brain can inhibit your gut function,” he added. “But it’s also true that disorders of the gut themselves can cause these mood disturbances. For example, we’ve shown that if you irritate the stomach in mice, it will show later. [signs] of anxiety and depression. And if you cut the vagus nerve, you can reverse this anxiety and depression.”

Some studies suggest that some aspects of anxiety and depression may also have their origin in the gut in humans.

representation of a group of foods high in omega-3 fatiStock.com/fcafotodigital

The link between the gut and cognitive health

Our gut health not only affects our mood, but can also affect our cognitive health, which can play a role in many conditions, including dementia, Alzheimer’s disease, Parkinson’s disease and autism spectrum disorder (ASD).

Several studies have shown a link between the microbiota in our gut and cognitive function. While the exact reasons why are not yet known, scientists believe that some chemicals made in the gut, called short-chain fatty acids, play a role in keeping our brains healthy. In fact, animals fed one of these short-chain fatty acids called butyrate developed some protection against vascular dementia. Short-chain fatty acids also play a role in the progression of Alzheimer’s disease.

The diversity of the microbiota in your gut also affects memory. There is some evidence that animals with less diversity in their microbiome, which can be caused by antibiotic treatment, often have impaired memory and working memory.

Similarly, there is evidence from mouse studies showing that a protein thought to contribute to Parkinson’s development originates in the gut and travels to the brain via the vagus nerve, Pasricha explains.

In addition, the composition of the gut microbiota in mice with behaviors similar to those in people with ASD has been shown to differ from those who do not exhibit that behavior. This is interesting when you consider that people with ASD have more gastrointestinal problems than average.

How can we improve our gut health?

Because our gut plays such an important role in our health, the good news is that there are steps you can take to improve your gut health. Diet, exercise and sleep all affect your microbiome. Eating a balanced diet, especially a diet high in fiber, is important for a healthy gut.

“Having a rich diversity of microorganisms in the gut is usually associated with better mood and better brain health,” Batheja said. “Many probiotic organisms depend on carbohydrates and fiber. We need to feed those good bacteria with good food. Try a plant-based diet, with a wide variety of fruits and vegetables. Remember the Mediterranean diet and avoid red meat.”

Exercise is also important for gut health. In fact, moderate exercise can help improve the diversity of bacteria in your gut and the microbial metabolites produced in your GI tract. Batheja added that exercise can boost important hormones such as serotonin and dopamine.

Maintaining a healthy lifestyle with a balanced diet, exercise, and good sleep habits can help us keep our microbiome in check, which in turn can help improve our mood and overall brain health.

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