How your gut and brain talk to each other, and why a balanced gut matters.
Your gut and brain are in constant conversation. Open one section at a time.
About 7 min read
Your gut and your brain are in constant, two-way conversation. This network is called the gut–brain axis. It links your digestive system and your brain through nerves, hormones, the immune system, and chemicals made by the microbes that live in your gut.
The vagus nerve carries signals between the gut and the brain in both directions. Most of its fibers (about 80% by commonly cited estimates for the whole nerve) carry information up from the body to the brain, so the brain is constantly “listening” to the gut. The gut also has its own network of hundreds of millions of nerve cells, called the enteric nervous system, which helps run digestion. It is sometimes called the “second brain.”
The body’s stress system affects digestion, and signals from the gut can feed back to influence stress and mood. This is one reason stress can upset the stomach, and why digestive problems may make people feel more anxious.
A large share of the body’s immune tissue sits along the gut, and gut microbes help train it. When the microbes or the gut lining are out of balance, inflammation in the body can rise, and inflammation has been linked to changes in mood.
When gut microbes ferment fiber, they make short-chain fatty acids such as butyrate, which feed the cells of the gut lining and help calm inflammation. Microbes can also make or influence some brain chemicals, such as GABA. In studies in mice, these fatty acids also helped keep the blood–brain barrier intact and supported the normal development of microglia, the brain’s immune cells. Most of this evidence comes from animal research.
Your microbiome is the community of trillions of microbes, mostly bacteria, living in your digestive tract. A healthy community tends to be diverse, with many kinds of microbes doing different jobs. They help digest food your body cannot break down on its own, make vitamins and fatty acids, support your immune system, and help keep harmful microbes in check.
When that community loses diversity or shifts toward more harmful microbes, scientists call it dysbiosis, or an imbalance. Things that can contribute include eating little fiber and many highly processed foods, antibiotics, long-term stress, poor sleep, infections, heavy alcohol use, and some medications. Antibiotics are sometimes essential, so take them only as prescribed.
Digestive symptoms such as bloating, constipation, or diarrhea; more inflammation; changes in immune function and nutrient absorption. Gut imbalance has been linked to irritable bowel syndrome, inflammatory bowel disease, and metabolic conditions, although not every link has been shown to be a cause.
People with depression often have different gut microbe patterns than people without it. In a 2019 study of over 1,000 people, Coprococcus and Dialister bacteria were lower in people with depression, even after accounting for antidepressant use. This shows an association, not that bacteria cause depression. Reviews also commonly report fewer Lactobacillus, Bifidobacterium, and short-chain-fatty-acid-producing bacteria in people with depression and anxiety, but most studies are small or compare groups at one point in time, so cause and effect are still unresolved (Ataei et al., 2025). Human trials of ways to change the gut to help mood are still early and mixed.
The link between the gut and mood is also seen in people with irritable bowel syndrome (IBS). In a 2019 review of 73 studies, about one in four people with IBS had an anxiety disorder and about one in four had a depressive disorder, and they were roughly three times as likely as others to have either. The influence runs both ways: stress and low mood can change how the gut works.
Researchers are also studying gut–brain links in neurological conditions. In Parkinson’s disease, one hypothesis is that abnormal proteins may begin in the gut and travel up the vagus nerve to the brain. Experiments in mice support this idea, but it has not been proven in people, and the human evidence is mixed.
Sources for the gut–brain section
Within Your Light is an educational platform. We do not provide medical advice, diagnosis, or treatment recommendations. This page is for educational purposes only and is not a substitute for professional medical advice. Always consult a healthcare provider before making significant dietary changes or if you have concerns about your mental health.
