Are the Gut and Brain One Body? Gut-Brain Axis Imbalance: Why Stress Harms the Gut and Extends to the Brain

Modern medicine explains our ancestors' wisdom through the concept of the gut-brain axis. The brain and the gut do not merely share a simple connection; they maintain an organic relationship exchanging information in real time, much like a massive highway. At the heart of this communication lies a cranial nerve called the vagus nerve. Originating in the brain, the vagus nerve extends to the heart, lungs, and our gut, serving as a critical pathway that transmits neurological messages between the brain and the gut. When we experience stress, the brain perceives it as a threat and immediately secretes the stress hormone cortisol. This cortisol does not affect only the brain; it flows to the gut, where it can increase intestinal mucosal permeability and trigger an inflammatory response. It also negatively affects the gut microbiota environment, decreasing beneficial bacteria and increasing harmful bacteria. This disrupted gut microbiota balance confuses our body's immune system and directly impairs the production of serotonin, the happiness hormone synthesized in the gut. About 90% of the serotonin in our body is made in the gut. This is an important reason why a healthy gut is necessary for a relaxed mind and a good mood. Pro-inflammatory substances produced in the gut or imbalances in neurotransmitters can be transmitted to the brain via the vagus nerve, potentially leading to brain hypofunction, reduced cognitive ability, and mental health issues such as anxiety or depression. When gut health deteriorates, it can even affect the brain's immune response, inducing impaired concentration or memory impairment, often referred to as brain fog. In this way, the gut and the brain continually influence each other, virtually functioning as one body. The vicious cycle where stress ruins the gut and the damaged gut in turn lowers brain function often serves as the root cause of chronic indigestion, irritable bowel syndrome, and unexplained fatigue and anxiety in modern people. Rather than a problem to be solved with just a few digestants, it is time to pay attention to the balance of the whole body, especially the communication between the gut and the brain.