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 event 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 mind and the gut—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 assistant professor of medicine in the UNC departments of medicine and nutrition. “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 Brain-Gut Connection
Although your brain is the control center for all bodily functions, when it comes to emotions such as nerves, stress, anxiety or depression, your second brain might also have a hand in how you’re feeling.
That’s right: The “second brain,” or the enteric nervous system (ENS), which governs digestion, has much to do with the way you handle distressing emotions.
The ENS—which is made up of 200 to 600 million nerve cells—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 too full, or when something we’ve eaten doesn’t agree with us. The ENS works alongside the complex ecosystem of microbes in the gut — collectively known as the intestinal microbiota—that reside in close proximity to the ENS. It is believed that interactions between the ENS and the intestinal microbiota may result in communication between our brain and gut.
Recent research suggests that gut microbes may affect our mood and behaviors, suggesting that the ENS may be even more like a brain than was previously believed. It has been shown that the levels of neurotransmitters like serotonin—which is known to regulate anxiety, happiness and mood—can be influenced by an organism’s intestinal microbiota. Even more interesting: The intestinal microbiota can directly produce neurotransmitters, the chemical messengers that transmit signals between synapses in your brain and nervous system. What effect these intestinally produced neurotransmitters might have is a question researchers are just beginning to explore.
“Neurotransmitters are essential for communication between the brain and the gut, and they can be produced by the intestinal microbiota,” Dr. Carroll says.
Microbes and Anorexia Nervosa
Our growing understanding of the relationship between the brain and the gut has yielded some surprising experimental data. UNC School of Medicine researchers have conducted studies that suggest changes to the intestinal microbiota resulting from anorexia nervosa may be linked to psychological symptoms—such as anxiety and depression—that are associated with the eating disorder.
“It may seem a little wild, but one of our ultimate goals is to be able to target specific microbes in order to help patients overcome the psychological symptoms associated with anorexia,” Dr. Carroll says. “And that’s where we’re headed; right now we’re just trying to figure out the relationship.”
Dr. Carroll’s work dives deep into how the brain and the microbes in the gut interact. As part of his research with the Center of Excellence for Eating Disorders (CEED), Dr. Carroll and his team colonized germ-free mice, which have lived their entire lives in a sterile environment, with the microbes from patients with anorexia nervosa, and then observed the changes in their body composition.
“We have had some very promising preliminary data,” Dr. Carroll says. “We’re beginning to learn what the intestinal microbiota’s contribution is to changes in weight, and in the future what its contribution is to anxiety and depression, and which specific microbes are having these effects. Ultimately, we’d like to be able to target them to encourage growth of the beneficial species and discourage the growth of the bad species that influence the disease.”