Gut instincts: unlocking your second brain

June 30, 2017
We've all experienced the curious "butterflies" in our stomach, or had a "gut feeling" about something, but what do those feelings mean? According to some gastroenterologists, the nervous system that runs your belly does much more than help process the food you eat – it essentially acts as a second brain.

As science delves ever deeper into the mysteries of our insides, there is an emerging view that the vast ecosystem of neurons and bacteria operating in our guts has a much bigger influence on how we feel and think than previously understood.

This notion of the gut as a separate brain is becoming more widely accepted among researchers, as evidenced by the appearance of a new field of study, called neurogastroenterology that aims to discover more about the way it works.

“The enteric nervous system (ENS) in the gut is incredibly complex, and mirrors many of the same activities we see in the brain,” says Karlee J. Ausk, M.D., gastroenterologist at Swedish Medical Center. “The ENS is made up of over 100 million neurons, more than in the spinal cord. And even though it’s governed by the brain and greater central nervous system, the network of nerves in the ENS is so extensive, in some ways it operates as an independent organism. And unlike involuntary functions like heart rate and breathing, the gut has a direct effect on emotions and vice versa. It’s as if the gut has a mind of its own.”

While the gut doesn't actually have the power of independent thought, the millions of nerves in this secondary nervous system take on a whole host of interior tasks and messages that the brain doesn't need to manage directly. What scientists are finding out, however, is that the gut does much more.

“We know that the brain-gut connection is operating all the time,” says Ausk. “The network of neurons and chemicals in the gut tells the brain when it’s hungry or sick. But the ENS also records experiences and emotions and transmits this information back to the brain. We may think of stress as all in our heads, but these impulses could very well be coming from the opposite direction.

“This connection is called the gut-brain axis, and it goes a long way toward explaining why we experience ‘gut feelings’ so strongly, or get that ‘sinking feeling’ in the pit of our stomachs when we think we’re about to get bad news.”

That gut feeling can worsen as the situation worsens. When people experience extreme stress, for example, the "higher" brain may act to protect the gut by signaling immunological cells to secrete histamine and prostaglandin; this mechanism prepares the gut for any needed self-repairs. While the resulting inflammation is a protective response, it also causes the familiar nervous stomach and cramping that comes with high levels of stress.

Research on the gut-brain connection is raising new possibilities for treating certain conditions, such as irritable bowel syndrome or chronic constipation. Additionally, intriguing new evidence shows that the brain may be “aware” of the type and number of bacteria in the gut, and because certain bacteria are known to affect serotonin levels, this, in turn, may lead to finding new ways to treat mood disorders.

While this mysterious communication between the brain and gut bacteria may suggest an alien intelligence working behind the scenes without our knowledge, it’s really about new ways to understand how the body manages and takes care of itself.
“This research into the gut-brain connection shows promise in unlocking how certain diseases work so that we can find new ways to prevent and treat disease,” adds Ausk. “I have a gut feeling that getting to know the second brain better may be the key to a whole new way of promoting wellness.”


If you are experiencing digestive problems, or have questions about mood disorders, find a doctor who can help you in our provider directory.

Read other articles with Dr. Ausk:

Gut bacteria and your kid's immune system 
5 fast facts about ulcerative colitis