Modern medicine is uncovering the secret of the link between the mind and the gut discussed in Donguibogam by explaining it through the concept of the brain-gut axis. The brain and the gut are not simply independent organs, but exchange their states with each other like close friends in constant conversation. This communication takes place largely through two pathways.
The first is the vagus nerve. Starting from the brain, this nerve passes through the neck and chest and connects directly to the intestines, immediately delivering stress or emotional changes felt by the brain straight to the gut. When stressed, the sympathetic nervous system is activated in the brain, which directly affects the movements, or peristalsis, and secretory functions of the intestine. An excessively activated sympathetic nerve abnormally accelerates or reduces intestinal motility, causing diarrhea or constipation, and increases intestinal mucosal permeability, worsening inflammatory responses.
The second is the exchange of neurotransmitters and hormones. The gut possesses its own neural network known as the enteric nervous system, earning it the name 'second brain', and about 90% of serotonin, known as the happiness hormone, is produced in the intestines. The brain and gut interact by exchanging various neurotransmitters such as serotonin, dopamine, and norepinephrine. In stressful situations, stress hormones such as cortisol are secreted from the brain, and these hormones influence the secretion and absorption of serotonin in the intestine, disrupting intestinal motility and causing changes in the gut microbiota environment. Gut microbiota is a key element of intestinal health; when the balance between beneficial bacteria and harmful bacteria is disrupted, intestinal inflammation responses increase, which in turn adversely affects brain function, potentially inducing anxiety and depression.
This complex interaction of the brain-gut axis clearly explains why patients with irritable bowel syndrome experience more severe abdominal pain, diarrhea, constipation, and abdominal distension in stressful situations. When the brain receives stress, the gut becomes unstable, and the unstable gut sends discomfort back to the brain, continuing a vicious cycle. Therefore, to treat irritable bowel syndrome, rather than merely addressing bowel symptoms alone, an integrative approach that restores the overall balance of body and mind—such as stress management, mindfulness, and the creation of a healthy gut microbiota environment—is essential.
