The Connection Between Your Brain and Your Gut

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This story originally ran April 4, 2018 and was updated May 15, 2024.

We’ve all been there. You have a big presentation to give or a difficult conversation to have, and your stomach is jumpy in anticipation. You wonder if you’re going to be sick counting down the minutes to whatever you’re dreading. Your brain seems to be sending your stomach a message: Something scary is coming.

Conversely, you may have noticed that when you have indigestion, maybe after overindulging in a fatty meal, it’s hard to concentrate. This time, it’s your stomach affecting your brain.

Turns out, these two body parts—the gut and the mind—are “talking” all the time.

“We’ve known for decades that there’s a connection between the gut and the brain. We call it the gut-brain axis,” says Ian Carroll, PhD, an associate professor in the Department of Medicine at the UNC School of Medicine and in the Department of Nutrition at the UNC Gillings School of Global Public Health. “This idea—that a feeling from the gut can manifest in the brain—is even part of our language, like when we talk about ‘gut feelings’ or ‘going with your gut.’”

The Gut-Brain Connection

Although your brain is the control center for all bodily functions, when it comes to nerves, stress, anxiety or depression, your second brain might also have a role in how you’re feeling.

That’s right: The “second brain,” or the enteric nervous system, which governs digestion, has much to do with the way you handle distressing emotions.

The enteric nervous system is made up of 200 million to 600 million nerve cells. It takes care of the day-to-day activities of digestion independently of the central nervous system and lets us know when we’re hungry or full, or if something we’ve eaten doesn’t agree with us. The enteric nervous system works alongside the complex ecosystem of microbes in the gut—collectively known as the intestinal microbiota—that reside in close proximity to the enteric nervous system. It is thought that interactions between the enteric nervous system and the intestinal microbiota may result in communication between the gut and brain.

Research suggests that gut microbes may affect our mood and behaviors, indicating that the enteric nervous system is more like a brain than experts previously believed. It has been shown that intestinal microbiota can influence the levels of neurotransmitters such as serotonin—known to regulate anxiety, happiness and mood. Even more interesting, intestinal microbiota can directly produce neurotransmitters, the chemical messengers that transmit signals between synapses in your brain and nervous system.

“Neurotransmitters are essential for communication between the brain and the gut, and they can be produced by the intestinal microbiota,” Dr. Carroll says.

In 2013, researchers coined the term “psychobiotics” for live bacteria that people can eat to increase the gut microbes that produce these neurotransmitters, with the goal of improving mental health and treating psychiatric disorders. Although researchers continue to study which specific bacteria may be best for mental health, you can reap some of the brain benefits by eating foods or using supplements that include probiotics and prebiotics, which foster a diverse, healthy gut microbiome.

Microbes and Anorexia Nervosa

Understanding the gut-brain connection could yield new insights and treatments for the eating disorder anorexia nervosa.

“When you severely restrict your nutrition, the gut microbes change,” Dr. Carroll says.

These changes could explain the psychological symptoms associated with anorexia, including anxiety and depression, but understanding the gut microbiome could be key to reducing the risk of relapse after treatment.

“If a person has severe anorexia and has a weight that’s lower than 75 percent of their ideal body weight, it would be recommended that they receive inpatient care where the focus will be on renourishment,” Dr. Carroll says. “They would receive a certain amount of calories that would increase until they gained weight that put them at 85 percent of their ideal body weight.”

Dr. Carroll says the renourishment process can be painful, causing bloating and cramping. The approach may also be psychologically distressing to someone who does not want to gain weight or who experiences anxiety at the thought of consuming several thousand calories per day, which increases the risk of relapse in disordered eating. It may also not be the best treatment for a changed gut microbiome.

“When the gut is in dysfunction after calorie restriction, its ability to absorb calories has changed,” Dr. Carroll says. “The renourishment will be ineffective if the gut can’t absorb it properly.”

Instead, Dr. Carroll is interested in studying the impact of using microbiota-directed complementary foods, or MDCFs, designed to influence the gut microbiome as a more precise form of renourishment, rather than simply relying on a number of calories consumed. Such supplements have been effective in trials treating malnourished children, but more research is needed to determine the right approach for people with anorexia.

“It’s possible that if we target the gut microbiota, we could reestablish a normal gut and help a person put on weight faster in a healthier manner,” Dr. Carroll says. “This approach could increase the function of the gut and the brain in tandem.”

People with anorexia nervosa would still need cognitive behavioral therapy in addition to these supplements, he says, but a better-targeted approach to renourishment could reduce stress and anxiety about the treatment.

“The ideal treatment for an individual with anorexia nervosa would include a faster recovery and an ability to maintain a healthy weight, as well as a reduced risk of relapse,” Dr. Carroll says. “Restoring gut function and targeting the microbiota could be central to those issues.”

If you have questions about your gut health or concerns about your mental health, talk to your doctor. Need a doctor? Find one near you.The post The Connection Between Your Brain and Your Gut first appeared on UNC Health Talk.

Brain Health, Digestive Health, Eating Disorders, Nervous System