The gut-brain axis is the two-way communication between your gut and brain². It is how your brain “knows” that you are hungry, how your belly “tells” your brain that it is full, and how your body “knows” to relax and digest the food once you’ve eaten.

But, the gut-brain axis goes beyond digestion. This two-way street between the gut and the brain is also why you may get butterflies in your belly when you’re nervous, why you feel like your belly is in knots before an important presentation, and even, for some people, why you may feel the need to poop when frightened¹. The thoughts and feelings processed in your brain can also impact the activity of your gut^{1, 2}.

What Does the Gut-Brain Axis Do?

The gut-brain axis helps govern numerous aspects of human health, including²:

• Gastrointestinal motility, i.e., controlling everything that happens with food in your body from the moment you put it in your mouth
• Digestion
• Metabolism
• Energy balance (homeostasis)
• Immunity and protecting the intestines from harmful bacteria
• Stress regulation

Emerging evidence suggests that the gut-brain axis also plays a key role in:

• Emotional regulation^{1, 2}
• Cognition and brain development⁶
• Mental health²

How Does the Gut-Brain Axis Work?

The gut and the brain are of course, connected anatomically or physically. But they are also connected through several complex systems and biochemical pathways, which make up the gut-brain axis. So let’s break them down.

We have a central nervous system, which is made up of the brain and spinal cord, and an enteric nervous system, which is a network of neurons that governs the gastrointestinal tract. Yes, we have neurons in our gut!

These two systems are connected through the gut-brain axis, which, in turn, is made of²:

• The autonomic nervous system, which regulates breathing, heart rate, and digestion
• The hypothalamic-pituitary-adrenal (HPA) axis, which helps control reactions to stress
• The vagus nerve
• The nerves in the gastrointestinal tract
• Hormones, neurotransmitters, and peptides
• The gut microbiota, that is, the trillions of microorganisms that live inside our gut

The gut-brain axis includes the following routes of communication:

• Endocrine, or related to glands and their secretions
• Humoral, or related to bodily fluids that play a role in immunity
• Metabolic
• Immune

Through these complex networks of nerves, neurons, glands, and biochemical pathways, the brain can influence what’s happening in your gut, and the gut can influence your mood, cognition, and mental health².

The Gut-Brain Axis and the Vagus Nerve

The vagus nerve is key in the communication between the gut microbiota and the brain⁵. The vagus nerve starts in the brain stem and travels all the way through the neck and rib cage down to the abdomen³. (Because it “travels” so much, it is also called the “wanderer nerve.”) So, it communicates information from the emotional and cognitive centers in the brain to the intestines and vice-versa.

In the intestines, it regulates the contraction of muscles and the secretion of glands. Overall, the vagus nerve is responsible for governing several processes, including³:

• Digestion
• Heart rate
• Breathing rate
• Swallowing
• Vomiting

The vagus nerve is also connected and sends neural signals to the HPA axis, which helps you adapt to stress³. Together, the vagus nerve and the HPA axis help the brain influence the activity of cells in the intestines. These cells play important roles in immunity, muscle contraction, and the health of bodily tissues, among other things³.

These very same cells, in turn, are influenced by the gut microbiota. The gut microbiota hosts several microorganisms, including “good” bacteria, viruses, and yeasts. More and more, research suggests that gut microbiota plays a key role in anxiety and depression³, and it’s all mediated by the vagus nerve⁵.

Is There a Link Between Gut Health and Anxiety?

Yes, evidence points to a link between gut health and mental health problems, including anxiety². There is an established connection between gastrointestinal problems and the following conditions^{1, 2}:

• Depression
• Anxiety
• Panic disorder
• Post-traumatic stress disorder (PTSD)

This link may be explained by what’s living inside the gut, i.e., our gut microbiota. For instance, some probiotics (live bacteria and yeasts that are thought to help restore the balance of bacteria in your gut) have improved well-being and decreased anxiety and distress in mouse and human studies³.

Also, the connection goes both ways. Not only does our gut microbiota influence our mood, but intense emotions can also affect our gut health.