People often feel a “knot” in their stomach when they’re nervous, whether they’re about to go on stage to give a speech or take the field for a championship game. Stress and anxiety can also cause nausea, painful bloating, constipation and diarrhoea.
This phenomenon is often called “nervous stomach” – but what exactly causes it?
Nervous stomach occurs because of the close connection between the nervous system and the digestive system, Melissa Hunt, a clinical psychologist at the University of Pennsylvania, told Live Science in an email.
“From the earliest stages of embryonic development, the brain, spinal cord and digestive tract are tightly interconnected,” she said. “Millions of neurons send information from the gut to the brain, and just as many neurons send signals back to the gut.” This connection is often referred to as the gut-brain axis.
The neurons or nerve cells lining the gastrointestinal tract make up the enteric nervous system. They are part of the ‘autonomic’ nervous system, which regulates involuntary body functions such as breathing, heartbeat and digestion. For example, when food enters the gut, enteric neurons tell muscle cells to contract and push the food through the intestines, according to Harvard Health.
The autonomic nervous system is divided into two branches: the parasympathetic and the sympathetic. These systems, nicknamed the ‘rest and digest’ and ‘fight or flight’ systems respectively, balance each other out. In general, the parasympathetic nervous system relaxes the body, while the sympathetic nervous system increases the body’s response to danger.
“Digestion is controlled by the parasympathetic branch,” says Hunt. “When we’re stressed, the sympathetic branch is activated and suppresses the functions of the parasympathetic system.” In this state, the body releases stress-related hormones such as cortisol, which suppress digestion in the stomach and small intestine, while other hormones actually stimulate the colon.
“So instead of entering a relaxed state associated with rest and digestion, the stomach and intestines may suddenly spasm or contract as the person prepares to fight or flee,” says Hunt.
Just as stress can trigger an upset stomach, frequent gastrointestinal (GI) problems can also cause stress, according to Harvard Health.
What’s more, stress can increase the frequency or severity of symptoms in “disorders of gut-brain interaction”, or DGBIs. These include conditions such as irritable bowel syndrome (IBS), in which a variety of symptoms such as abdominal pain, diarrhoea or constipation occur without a clear cause, or functional dyspepsia, stomach pain that occurs during or after eating for no known reason.
DGBIs are thought to be characterised by persistent disturbances in communication between the gut and the brain. Over time, people can become anxious and hypervigilant about their GI symptoms, Hunt said.
“This leads to visceral hypersensitivity, which becomes a vicious feedback loop of anxious arousal, scanning the body for uncomfortable sensations, catastrophizing, amplifying those sensations, which increases anxiety and then leads to increased GI discomfort and distress,” she said.
That’s why, according to Harvard Health, behavioural therapy is sometimes included in patients’ treatment plans for GI disorders.
