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When you feel that fluttering excitement, many of us say we have "butterflies in our stomach." While the origin of the phrase is uncertain, it entered common usage in the early 20th century, first appearing in a 1908 publication. In reality, this sensation is a neurobiological response, not a mystical one. It emerges from the gut–brain axis, a continuous dialogue between the central nervous system (brain and spinal cord) and the digestive system.
What makes this connection remarkable is the sheer number of neurons residing in the gut—over 160 million, roughly comparable to the 200 million neurons in the spinal cord. This complex network, known as the enteric nervous system or the "second brain," orchestrates many autonomic functions and communicates directly with the brain.
A key player in the gut–brain axis is the gut microbiome, the community of microorganisms—primarily bacteria—inhabiting our intestines. Recent research shows that these microbes help regulate stress responses, and in turn, stress can alter the composition of the microbiome. This bidirectional relationship may explain why certain gut bacteria, such as Streptococcus, are linked to higher anxiety levels.
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During stressful moments, the sympathetic nervous system is activated, triggering a "fight-or-flight" response. Hormones such as adrenaline (epinephrine) and noradrenaline (norepinephrine) shift the body’s focus away from digestion to prepare for immediate action. Some scientists believe that the hormonal surge and its impact on gut microbial balance produce the characteristic butterfly feeling.
Alterations in gut microbiome composition are implicated in several neurological conditions, including anxiety disorders. Strong associations exist between anxiety and chronic gastrointestinal issues like irritable bowel syndrome, and a lack of microbial diversity has been observed in anxious individuals. Certain gut bacteria have been identified as potential contributors to heightened anxiety.
While a mild nervous excitement—such as that experienced around a crush—is normal, chronic or intense stress can interfere with daily functioning. If you notice persistent discomfort in your gut or other physiological symptoms, it is wise to consult a healthcare professional and consider stress-reduction strategies.
