Why you get butterflies in your stomach when you're nervous

A feeling everyone knows

Before a job interview, a first date, a big presentation or the opening kickoff, your stomach seems to react before you do. English even has a name for it: butterflies. The expression has a real basis. Your digestive system responds to what your brain is feeling.

Read also: The Mandela Effect: why so many people remember it wrong and Why do we yawn when we see someone else yawn?.

The gut-brain axis

A review in Nature Reviews Neuroscience describes two-way communication between the brain and the gut through nerves such as the vagus nerve, hormones and the immune system. Stress changes how the gut works, and signals coming from the gut also influence the brain.

Source: Mayer, Gut feelings: the emerging biology of gut–brain communication, Nature Reviews Neuroscience, 2011.

What happens when you are nervous

In the fight-or-flight response, the body diverts energy toward muscles, heart and breathing. Digestion takes a back seat, which can bring that fluttery, hollow, tight or slightly queasy feeling. It is a normal response, and it passes when the moment does.

When the connection becomes a symptom

For most people, butterflies fade along with the nerves. For some, though, the gut-brain line stays oversensitive. Doctors now call this group of conditions disorders of gut-brain interaction, and irritable bowel syndrome, or IBS, is the best-known example.

The review behind the Rome IV criteria, used by gastroenterologists worldwide, describes how stress, gut sensitivity and the way the brain interprets those signals combine to produce real pain and discomfort, even when tests show no visible damage.

Source: Drossman, Functional Gastrointestinal Disorders and Rome IV, Gastroenterology, 2016.

A simple way to calm your body

Breathing is one of the few parts of the stress response you can steer on purpose. In diaphragmatic breathing, also called belly breathing, air comes in through the nose and your belly, not your chest, expands. Then you breathe out slowly, a little longer than the inhale.

In a study of healthy adults published in Frontiers in Psychology, people who practiced this kind of breathing over eight weeks had fewer negative emotions, better attention and lower levels of cortisol, the stress hormone, than a group that did not practice.

Source: Ma et al., The Effect of Diaphragmatic Breathing on Attention, Negative Affect and Stress in Healthy Adults, Frontiers in Psychology, 2017.

When to get it checked

Frequent discomfort, pain, diarrhea or bowel changes that do not go away deserve a visit to your doctor. See also anxiety signs in the body and how to recognize them.