The Gut–Brain Axis:
What It Is and How It Really Works
Your brain and your gut are in constant contact. This communication influences digestion, metabolism, immunity and mental wellbeing — and science is only beginning to reveal its full extent.
FAQ — Quick Reference
Here you will find answers to the most frequently asked questions about the gut–brain axis. Click on the question that interests you and go directly to the answer.
What is the gut–brain axis
The gut–brain axis is a two-way communication system connecting the digestive tract and the central nervous system. Communication occurs via neural pathways, hormones, immune mechanisms and substances produced by the gut microbiome. Current research suggests that this mutual communication may influence digestion, metabolism, immune response and certain aspects of mental health.
The gut–brain axis represents a complex biological communication system connecting the digestive system with the central nervous system. While it may seem that the brain merely controls gut activity, current understanding shows that communication is bidirectional. Information is continuously transmitted from the gut to the brain and from the brain back to the digestive tract via neural pathways, hormones, immune mechanisms and substances produced by the gut microbiome.
This communication system helps the organism respond continuously to changes in its internal and external environment. The brain, for example, influences intestinal motility, the production of digestive juices and the permeability of the gut barrier, while the gut provides the brain with information about nutrient availability, microbiome composition, immune system activity and the organism's current metabolic state.
For a long time, the role of the gut was associated primarily with digestion and nutrient absorption. Research over the past two decades has shown, however, that the gut is one of the most active communication organs in the human body.
The intestinal wall contains an extensive network of nerve cells known as the enteric nervous system, sometimes nicknamed the "second brain". This system contains hundreds of millions of neurons and is capable of independently controlling numerous digestive functions. It is also closely connected to the central nervous system, particularly via the vagus nerve.
The growing interest among scientists is linked primarily to the rapid development of methods enabling detailed study of the gut microbiome and its metabolic activity. Modern genetic and metabolomic analyses show that microbiome composition varies significantly between individuals.
At the same time, an increasing number of studies suggest associations between changes in the gut environment and certain chronic diseases or psychological difficulties. It is important, however, to distinguish between association and causation. In many cases it is not yet clear whether microbiome changes represent a cause of health problems, a consequence, or merely one of many factors.
Unlike genetic information, the gut–brain axis is not immutable. Its functioning can be influenced by a range of factors — diet composition, fibre intake, sleep quality, chronic stress and regular physical activity.
How the Gut–Brain Axis Works
The gut–brain axis is not a single neural pathway or a single biological mechanism. It is an extensive communication network in which the nervous system, hormones, the immune system and the gut microbiome are continuously interconnected.
Communication occurs continuously in both directions. The brain sends signals influencing gut activity, while the gut continually provides the brain with information about what is happening in the digestive tract.
Nerve Communication (Vagus Nerve)
The fastest connection between the gut and brain is provided by the vagus nerve. Surprisingly, the majority of its nerve fibres do not carry commands from the brain to the gut, but rather transmit information from the gut to the brain. The enteric nervous system contains 200–600 million neurons and can coordinate digestion entirely on its own.
Hormonal Communication
The gut is one of the largest endocrine organs in the human body. Specialised mucosal cells produce GLP-1, PYY, cholecystokinin (CCK) and other hormones that regulate food intake and satiety. Under stress, the HPA axis is activated, leading to increased cortisol production that affects the entire digestive system.
Immune Communication
Approximately 70% of adaptive immune system cells are located in the intestinal mucosa. Communication produces cytokines — signalling molecules that can also influence the brain via the bloodstream. Research is investigating their role in chronic inflammation and neurological conditions.
Microbial Communication (SCFA)
Micro-organisms produce hundreds of metabolites during food processing. The best-studied are short-chain fatty acids (SCFAs) — butyrate, acetate and propionate. These serve as an energy source for colon cells, help maintain the gut barrier and influence the immune system. The bacteria themselves do not travel to the brain — communication occurs through their metabolic products.
The Four Main Communication Pathways Connecting the Gut and BrainThe individual communication mechanisms do not function in isolation. A change in one part of the system can affect the others. This is not a simple linear relationship, but a complex network of interconnected processes.
Biological Role of the Gut–Brain Axis
The primary function of the gut–brain axis is to help the organism coordinate the activity of various organ systems. It connects the nervous system, metabolism, immune response and energy management into one functional whole.
The Biological Role of the Gut–Brain Axis and the Cycle of Mutual CommunicationWhat Current Science Says
Research on the gut–brain axis has undergone remarkably rapid development over the past two decades. Thanks to modern DNA sequencing and metabolomics methods, we now have a better understanding of how the gut and brain communicate. Nevertheless, it is important to distinguish well-established findings from areas that are still the subject of research.
One of the greatest advances in contemporary biomedicine is a shift in how the gut microbiome is viewed. It is no longer seen merely as a passive component of digestion, but as an active ecosystem that participates in metabolism, communication with the immune system and the production of biologically active substances.
This is one of the most frequently asked questions and also an area in which the most inaccuracies arise. Experimental animal studies have shown that changes in the gut microbiome can influence behaviour and stress responses. In humans, associations have been described between microbiome composition and certain psychiatric conditions.
This does not automatically mean that microbiome changes cause these conditions. In most cases it is not yet possible to reliably determine whether this is a cause, a consequence, or one of many contributing factors. Current professional bodies therefore recommend interpreting results cautiously.
Research into psychobiotics — probiotic micro-organisms or other interventions targeting the gut–brain axis — is attracting considerable attention. Some clinical studies suggest that selected strains may influence subjectively perceived stress or quality of life in some people.
Results are not uniform, however, and vary according to the bacterial strains used, the duration of administration and the population studied. The current consensus therefore does not yet support generalising the effects of all probiotics on mental health. One cannot speak of the "effect of probiotics" in general — each strain has different biological properties.
The relationship between gut barrier function and low-grade chronic inflammation is an intensively studied area. Experimental and clinical studies show that in some conditions, changes in gut barrier integrity can occur. It is not yet clear, however, whether these changes are a cause or a consequence.
It is therefore more appropriate to speak of associations rather than direct causal relationships.
We are still seeking answers to questions such as: What does a "healthy" microbiome look like in different populations? Why does the same probiotic work differently in different people? How does the microbiome influence lifestyle over the long term? Which microbiome changes are a cause and which are a consequence of disease? What role does the host's genetic makeup play? How can microbiome knowledge be applied in personalised medicine?
These are among the most actively researched areas in biomedicine.
Aburto MR, Cryan JF. — Nature Reviews Gastroenterology & Hepatology, 2024
Gastrointestinal and brain barriers: unlocking gates of communication across the microbiota–gut–brain axis.
Schneider E, O'Riordan KJ, Clarke G, Cryan JF, et al. — Nature Metabolism, 2024
Feeding gut microbes to nourish the brain: unravelling the diet–microbiota–gut–brain axis.
Mann ER, Lam YK, Uhlig HH. — Nature Reviews Immunology, 2024
Short-chain fatty acids: linking diet, the microbiome and immunity.
Horowitz A, Chanez-Paredes SD, Haest X, Turner JR, et al. — 2023
Paracellular permeability and tight junction regulation in gut health and disease.
Ross FC, Patangia D, Grimaud G, et al. — Nature Reviews Microbiology, 2024
The interplay between diet and the gut microbiome: implications for health and disease.
What Factors Influence the Gut–Brain Axis
No single factor determines the functioning of the gut–brain axis. It is a dynamic biological system that responds continuously to changes in nutrition, lifestyle and the surrounding environment. Every Person Is Unique — stejná strava, stejné probiotikum nebo stejný životní styl mohou u různých lidí vést k odlišným výsledkům.
Diet and Fibre Intake
A varied diet rich in vegetables, fruit, legumes and wholegrains provides micro-organisms with a substrate for fermentation. SCFAs are produced, contributing to the nutrition of colon cells. A monotonous diet low in fibre can lead to changes in microbiome composition.
Sleep Quality
Sleep is important not only for the brain, but also for the coordination of hormonal, metabolic and immune processes. Chronic sleep deprivation can influence gut microbiome composition and the regulation of hormones related to food intake.
Psychological Stress
One of the best-described pathways by which the brain influences gut activity. HPA axis activation leads to increased cortisol production, which can alter intestinal motility and gut barrier function. The relationship is bidirectional — changes in the gut also influence the stress response.
Physical Activity
Regular physical activity is associated with a range of beneficial effects on overall health. Some studies suggest it may also influence gut microbiome composition and its metabolic activity.
Antibiotics and Medications
Antibiotics are among the most significant factors altering gut microbiome composition in both the short and long term. The gut environment may also be affected by proton pump inhibitors, NSAIDs or metformin.
Age
Gut microbiome composition changes naturally throughout life — in early childhood, adulthood and older age. It is therefore not possible to define a single universal "ideal microbiome" applicable to everyone.
Genetic Predispositions
Genes influence the composition of intestinal mucus, immune system function and nutrient metabolism. However, genetics is only one part of the overall picture — environmental factors can be influenced to a considerable degree.
Fermented Foods
Yogurts with live cultures, kefir, sauerkraut and kimchi may contribute to increased microbial diversity. Study results are not uniform and cannot be automatically generalised to all fermented products.
Factors influencing the functioning of the gut–brain axisWhat Approaches Are Being Studied Today
The growing number of studies has led to the development of a wide range of research directions. It is important to emphasise that many of these approaches are still the subject of intensive research and their effectiveness may vary depending on the specific population, health status and method used.
Key takeaway from research: The most reliable evidence so far supports the importance of a varied diet, adequate fibre intake, quality sleep, regular exercise and the management of chronic stress. Other approaches, including probiotic or postbiotic interventions, remain the subject of further research.
Current research approaches for the gut–brain axisPractical recommendations
Research on the gut–brain axis shows that there is no single step or universal solution. Nevertheless, several general recommendations can be formulated that are consistent with the principles of a healthy lifestyle.
Practical steps to support the gut–brain axis — what to do todaySummary: What remember
The gut–brain axis is a natural communication system connecting the brain, digestive tract, immune system and gut microbiome. Through this mutual cooperation, the organism continuously coordinates digestion, energy use, immune defence and responses to everyday demands.
Current research shows that the functioning of this communication can be influenced by diet, sleep, exercise and chronic stress, among other factors. At the same time, it confirms that there is no single universal solution suitable for everyone. The best-evidenced foundation for caring for the gut–brain axis remains a varied diet, sufficient exercise, quality sleep and an overall healthy lifestyle.
The gut–brain axis — key points to rememberScientific Sources Used
This article draws primarily from review studies, systematic reviews and publications in peer-reviewed international journals.
Gastrointestinal and brain barriers: unlocking gates of communication across the microbiota–gut–brain axis.
Nature Reviews Gastroenterology & Hepatology. 2024;21(4):222–247.
Feeding gut microbes to nourish the brain: unravelling the diet–microbiota–gut–brain axis.
Nature Metabolism. 2024;6:1454–1478.
Short-chain fatty acids: linking diet, the microbiome and immunity.
Nature Reviews Immunology. 2024;24:577–595.
Paracellular permeability and tight junction regulation in gut health and disease.
Nature Reviews Gastroenterology & Hepatology. 2023;20:417–432.
The interplay between diet and the gut microbiome: implications for health and disease.
Nature Reviews Microbiology. 2024;22:671–686.
- Nature Reviews Gastroenterology & Hepatology — microbiome, gut barrier and gastroenterology
- Nature Reviews Microbiology — microbiology, microbiome and host–micro-organism interactions
- Nature Reviews Immunology — immunology, inflammation and microbial metabolites
- Nature Metabolism — metabolism, nutrition and the gut–brain axis
Care for Your Microbiome Naturally
Gutox, GUTHERB, Mumio and other products designed with an emphasis on clean composition and functional formulations. Free from unnecessary additives, tested in the Czech Republic.
