What to Know About the Gut Brain Link

Medically Reviewed by Minesh Khatri, MD on February 18, 2024
3 min read

Did you know that you have a second brain? And that it’s located inside of your gut? This is what causes you to feel emotions like getting butterflies when you’re excited or nervous, and feeling sick to your stomach when scared or emotional. This second brain is called the enteric nervous system (ENS). The ENS is made up of two thin layers that contain more than 100 million nerve cells. These cells line your gastrointestinal tract that runs from your esophagus all the way down to your rectum.

Your gut has several different parts, such as all of the different organs that aid in digesting food and then turning it into waste. The parts of the gut include:

  • Esophagus
  • Stomach
  • Small and large intestines
  • Gallbladder
  • Liver
  • Pancreas

The second brain in your gut, or the ENS, communicates directly with the brain in your head. This is called the brain-gut connection or gut brain link.

The ENS communicates with your brain both physically and chemically. These connections that go back and forth travel along a pathway called the gut-brain axis. Your gut’s main connection to the brain is the vagus nerve. This nerve also controls messages that are sent to the heart, lungs, and other organs. Additionally, hormones and other neurotransmitters travel along the gut-brain axis to send messages chemically.

These chemical messages are affected by your gut’s microbiome. This consists of all of the fungi, viruses, and bacteria that live inside your gut. There are many different kinds inside of your gut, some of which can be beneficial or harmful to your health. Others have no impact at all.

The gut-brain axis isn’t just your brain and the ENS. This pathway also involves your:

  • Endocrine system
  • Immune system
  • Hypothalamic-pituitary-adrenal axis
  • Microbiota
  • Metabolites 

The gut-brain link is shown to have an effect on your health when it comes to certain diseases or conditions. This includes both your physical and mental health, since the gut is your second brain.

Within the last 15 years, scientists have realized what an important role gut microbiota plays in your health. The microbiota is made up of trillions of microorganisms both within and on your body. The gut microbiota help to regulate the function of the gut-brain axis. The microbiota and brain communicate with each other through the ENS, vagus nerve, and other pathways.

Experts and researchers are currently studying the gut-brain link and its effect on certain neurological conditions. Microorganisms in your body help to regulate your immune system’s response. As such, certain illnesses are now being researched to understand what’s going on in the gut that may cause these conditions - or at least play a part in their development. These conditions include:

  • Multiple sclerosis
  • Parkinson’s disease
  • Alzheimer’s
  • Schizophrenia 
  • Autism
  • Anxiety
  • Pain
  • Amyotrophic lateral sclerosis

Besides neurological conditions, researchers are also taking a closer look at gastrointestinal (GI) conditions and how they affect the way your brain works.

Some factors early on in life can affect the composition of your gut microbiota and the microbes found inside of it. This includes:

  • Mode of delivery during birth
  • Infections
  • Host genetics
  • Using antibiotics
  • Nutrition
  • Environmental stressors

As you get older, the diversity of microbes in your gut goes down. High levels of stress at any time during your life also change the diversity of microbes in your gut.

The gut-brain link is what causes you to feel things like a fight or flight response and nervousness before giving a presentation. Many people deal with other conditions that affect their physical and gut health. If you feel things like anxiety or depression, this can cause intestinal distress, causing problems in the stomach or bowels. Because of the gut-brain link, the reverse can also be true — that your gut health is affecting your mental and physical health.

Your ENS can impact your emotions. In turn, your emotions can have an effect on certain conditions, like:

  • Irritable bowel syndrome (IBS)
  • Constipation
  • Bloating
  • Pain
  • Diarrhea
  • Stomachaches

For a long time, doctors thought that anxiety and stress were the root cause of these gastrointestinal problems, but it’s actually now thought to be the opposite. Poor gut health can send signals to the central nervous system and influence your mood.

Some people who experience gastrointestinal problems may have no other physical symptoms. The cause may be a side effect of their mental health, so trying to improve gut health can be difficult since stress and anxiety take a toll on a person both mentally and physically.