The interactions between the gut and brain, also known as the gut-brain axis, represent a very interesting area of research in modern medicine. It connects the central nervous system (CNS) with the enteric nervous system (ENS). The gut-brain axis plays an important role in the regulation of metabolic processes, the immune response and even mental health.
It's hard to believe, but while the brain has around 86 billion neurons, the gut is similarly complex with its enteric nervous system (ENS) - consisting of around 100 million nerve cells. This nervous system acts largely autonomously, controls digestion, processes signals and mediates reflexes. However, it also interacts continuously with the central nervous system (CNS), which underlines the importance of the intestine as a "second brain"
In addition to neuronal density, the ENS is closely linked to the CNS via chemical messengers, electrical impulses and immune cells. These networks influence not only physiological processes, but also emotional states and cognitive functions. It is therefore a very exciting field of research, which has already been much better researched than was the case ten years ago. However, it is still largely considered a "black box" and we can expect many more exciting findings from research into this connection, which have the potential to change both basic medicine and therapeutic approaches.
Which components play a role in the gut-brain axis?
To begin with, this overview should give you an idea of which components in our body are connected in the gut-brain axis and therefore have an influence on each other. A whole orchestra of processes is formed that interact here and if one of them doesn't play in time, this can affect the whole piece. We will go into more detail about the respective players in the following text.
Neurale Kommunikation
- The vagus nerve is the most important direct connection between the gut and the brain. It transmits signals in both directions and influences digestion, emotions and stress levels, among other things.
- The enteric nervous system, also known as the "gut brain", independently regulates many functions of the gastrointestinal tract.
Microbiome and metabolites
- The trillions of microorganisms in the gut (microbiome) produce neurotransmitters such as serotonin, dopamine and GABA, which can directly influence the brain.
- Short-chain fatty acids such asbutyrate , propionate and acetate have immunomodulatory and neuroprotective effects.
Endocrine (hormonal) communication
- The gut produces hormones such as ghrelin, leptin and peptides YY, which influenceappetite, mood and metabolism .
- The hypothalamic-pituitary-adrenal axis (HPA axis) reacts to stress and can be influenced by inflammationor intestinal dysbiosis .
Immunologische Interaktion
- The intestine is equipped with approx. 70% of the immune system.
- A disturbed intestinal barrier (leaky gut) can trigger inflammatory processes that are associated with neurological and mental illnesses.
The vagus nerve as the main connection
Thevagus nerve is the longest and perhaps most important nerve in our autonomic nervous system. It connects the brain with almost all vital organs - from the heart to the lungs to the intestines. In the past, the vagus nerve was mainly researched in neurology and cardiology, but today it is becoming increasingly apparent that it is not only responsible for controlling the organs, but also influences our mood, our immune system and even chronic inflammation . So it's no wonder that the vagus nerve is currently attracting enormous attention - both in science and in the media.
How does the vagus nerve influence the gut?
The vagus nerve is the direct communication route between the gut and the brain. Its fibers transport 80% of the signals from the gut to the brain- and only 20% in the other direction. This shows how strongly the brain is influenced by information from the digestive tract. These signals regulate numerous processes:
Digestion and intestinal motility
The vagus nerve controls the motility of the intestine by regulating peristalsis(the rhythmic contractions of the intestine). If it is weakened, this can lead to digestive problems such as constipation, bloating or even irritable bowel syndrome (IBS, inflammatory bowel disease) .
Inhibition of inflammation and the immune system
It activates the cholinergic anti-inflammatory reflex, an endogenous protective system against inflammation. If this mechanism is disrupted, chronic inflammation can develop, which plays a role in Crohn's disease, ulcerative colitis or autoimmune diseases.
Influence on the mood and nervous system
The vagus nerve influences the production of neurotransmitterssuch as serotonin, dopamine and GABA , which are important for our mood and mental performance. Impaired vagus activity is associated with depression, anxiety disorders and even neurodegenerative diseases such as Parkinson's.
Communication with the microbiome
Intestinal bacteria produce substances that are transmitted to the brain via the vagus nerve. A dysbiosis (imbalance in the microbiota)can lead to cognitive and emotional disorders via this mechanism. Dysbiosis is also one of the 12 hallmarks of ageing.
TENS training is also a variant of neuromodulation that works in a similar way to vagus nerve stimulation. With vagus nerve stimulation, however, the electrodes tend to be placed on the ear, neck or wrist.
How can the vagus nerve be stimulated?
Because the vagus nerve is so deeply involved in many bodily processes, research has focused intensively on possible forms of therapy. Some of these have already been officially approved or are being clinically tested. This field is also summarized as neuromodulation , about which we have already written a separate article.
Vagus nerve stimulation (VNS) - electrical activation of the nerve
Vagus nerve stimulation (VNS) is a medically approved therapy. This involves stimulating the nerve using electrical impulses - either via an implanted device or using a non-invasive method (e.g. via the ear region). This therapy is used for:
- Epilepsie
- Therapieresistente Depressionen
- Cluster-Kopfschmerzen
- (Investigated for) irritable bowel syndrome & chronic inflammation
Polyvagal therapy (Stephen Porges' polyvagal theory)
Focuses on activating the "ventral vagus" to reduce anxiety, trauma and digestive disorders . Applied techniques include breathing exercises, meditation, physical exercises and pressure points.
Natural methods for vagus nerve stimulation
- Deep breathing: Prolonged exhalation activates the parasympathetic nerve.
- Exposure to cold: Alternating showers or ice water baths increase vagus activity. The extreme athleteWim Hof in particular has made this practice very popular and written several books about it.
- Singing, humming, gurgling: Activates the vagus nerve via the larynx.
Why is the vagus nerve so present in the media right now?
The vagus nerve is currently on everyone's lips - both in scientific research and in the press. There are many reasons for this:
- Increase in stress-related illnesses: Chronicstress and burnout are on the rise worldwide, and the vagus nerve offers a natural way to calm the nervous system.
- New insights into the treatment of chronic inflammation: Studies show that low vagus activity is associated with silent inflammation (low-grade inflammation, orinflammaging ), which plays a role in autoimmune diseases, diabetes and cardiovascular disease.
- Trend in self-optimization & amp; biohackingscene: The vagus nerve is hailed as a "super nerve" - and methods such as breathing techniques, cold baths and vagus-activating diet and exercise have become popular trends.
The role of the gut microbiome
The gut microbiome as a key player of the gut-brain axis
The gut microbiome - the trillions of bacteria, viruses and fungi that live in our gut - has adirect influence on communication between the gut and brain . These microorganisms produce a variety of neurotransmitters, hormones and metabolites that communicate with the brain via thevagus nerve, the immune system and the endocrine system .
Healthy microbiota promotes mental well-being , whiledysbiosisis associated with mental and neurological disorders - meaning it can affect mood, stress levels and even concentration. Overgrowths of pathogenic microorganisms such as Candida or SIBO (Small Intestinal Bacterial Overgrowth) also often lead to symptoms such as bloating, diarrhea and nutrient deficiencies. Which substances are produced in the gut, what do they influence and which bacteria play a special role? We will now take a closer look at these questions.
Which substances are produced by the microbiome that are involved in gut-brain communication?
Communication between the gut and brain occurs via three main mechanisms :
1) Production of neurotransmitters and neuromodulators
Certain gut bacteria directly produce neurotransmitters that play a central role in our mood, cognition and gut motility. These include:
Serotonin (5-HT) – „Glückshormon“
- 90% of the serotonin in the body is produced by enterochromaffin cells in the intestine, which are regulated by intestinal bacteria.
- Producing bacteria: Escherichia coli,Enterococcus , Streptococcus, Lactobacillusand Bifidobacterium.
- Function: Regulates mood,sleep , appetite and bowel movements.
- Dysbiosis effects: Serotonin deficiency may be associated with depression, anxiety disorders and irritable bowel syndrome (IBS).
Dopamin – „Motivationshormon“
- Produced by Bacillus spp. and Escherichia coli .
- Function: Influences motivation, reward system and motor control.
- Dysbiosis effects: Dopamine deficiency is associated with Parkinson's disease, depression and ADHD.
GABA – „Entspannungshormon“
- Produced by Lactobacillus and Bifidobacterium .
- Function: Has an inhibitory effect on the nervous system, reduces stress and anxiety.
- Dysbiosis effects: Low GABA levels are associated with anxiety disorders and depression.
Acetylcholine - "learning and memory hormone"
- Produced by Lactobacillus spp.
- Function: Promotes memory processes and regulates the autonomic nervous system.
2) Production of short-chain fatty acids
Short-chain fatty acids are important metabolic products of the microbiome that have a direct influence on the brain.
butyrate (produced byFaecalibacterium prausnitzii,Roseburia and Eubacterium rectale). Has an anti-inflammatory effect, protects the intestinal barrier and promotes the production of the brain growth factor BDNF (important for learning & memory).
Propionate& acetate b influence the energy metabolism in the brain.
3) Modulation of the immune system and inflammatory reactions
The microbiome regulates the immune system via certain substances and influences the blood-brain barrier as well as inflammatory processes:
Lipopolysaccharides (LPS) (from gram-negative bacteria such asEnterobacterandEscherichia coli )
- Can damage the intestinal barrier ("leaky gut") and trigger inflammation throughout the body.
- Dysbiose-Auswirkungen: Chronic inflammation from LPS has been linked to depression, anxiety disorders, Parkinson's disease and Alzheimer's disease.
Tryptophan metabolites (e.g. indole, kynurenine)
- Determine whether tryptophan is broken down for serotonin (good) or neurotoxic kynurenine (bad).
- Imbalanced tryptophan metabolism is associated with sleep disorders, depression and cognitive impairment
Hormones and neurotransmitters: the biochemical language of the gut
The gut is a central endocrine organ and produces a variety of hormones that not only regulate digestion, but also influence hunger, satiety, metabolism and even mood. These hormones communicate directly with the brain via the gut-brain axis and influence our behavior and physiological processes throughout the body.
Hunger- und Sättigungshormone
The gut plays a crucial role in the regulation of appetite:
Ghrelin - the hunger hormone
- Produced in the stomach and small intestine, ghrelin increases appetite by signaling the brain that it's time to eat.
- S a level rises before a meal and falls after food intake.
Peptide YY (PYY) - the satiety hormone
- Is secreted in the lower small intestine and upper colon and signals to the brain that sufficient food has been ingested.
- It inhibits gastric emptying and reduces the feeling of hunger.
Glucagon-like peptide-1 (GLP-1) - the metabolic regulator
- Promotes insulin secretion and inhibits glucagon release, thereby lowering the blood glucose level .
- Slows gastric emptying and thus ensures a longer-lasting feeling of satiety.
- Because of its action, GLP-1 is a key component of modern drugs for the treatment of diabetes, obesity and insulin resistance .
Cholecystokinin (CCK) - the digestive helper
- CCK is produced in the I cells of the small intestine and plays a dual role: it stimulates the release of digestive enzymes from the pancreas and at the same time promotes a feeling of satiety.
Verdauungsregulierende Hormone
In addition to controlling appetite, the gut also regulates numerous digestive processes:
Gastrin sstimulates gastric acid production to promote the digestion of proteins.
Secretin wis released in the small intestine on contact with acidic stomach contents and ensures that the pancreas produces bicarbonate to neutralize stomach acid.
Motilin rregulates the so-called Migrating Motor Complexes (MMC), rhythmic contractions that take place between meals and cleanse the intestines. This function is currently the focus of much research and plays a special role in mal-colonization and irritable bowel syndrome.
Neuroactive hormones
The close connection between the gut and brain is mediated by a number of neuroactive hormones:
Serotonin - the happiness hormone
- About 90% of all serotonin is not produced in the brain, but in the gut.
- It controls intestinal motility, but also influences the central nervous system and therefore mood.
- Disrupted serotonin production is associated with irritable bowel syndrome, depression and anxiety disorders.
Cortisol (indirectly influenced by intestinal bacteria)
- Although cortisol is produced in the adrenal glands, the gut microbiome indirectly controls the stress response via the HPA axis, neurotransmitters and theimmune system. Healthy gut flora can help to cushion cortisol spikes, reduce inflammation and increase stress resistance - an important key to mental and physical balance.
The immune system and communication between the gut and brain
Around 70% of all immune cells are located in the gut , where they work in a highly sensitive interaction with the microbiome. If this balance is disturbed, the consequences can be fatal: Inflammatory substances from the gut enter the bloodstream and directly affect the brain
But how exactly does the immune system affect the gut-brain axis? And how can we specifically reduce inflammation to protect not only the gut but also the brain
The gut barrier - your immune defense on the front line
The intestinal mucosa is the first layer of protection against unwanted intruders. It decides which substances are allowed to pass into the bloodstream.
Tight junctions are tiny proteins that hold the intestinal cells together like a barrier - but they can become permeable in the event of inflammation or dysbiosis.
"Leaky gut" occurs when toxins, undigested food particles or bacterial components (e.g.lipopolysaccharides, LPS) pass through the intestinal wall into the bloodstream and trigger animmune reaction .
Inflammation as a silent threat to the brain
When the immune system is out of balance, it releases pro-inflammatory cytokines:
- Interleukin-6
- Tumornekrosefaktor-alpha
- Interleukin-1β
These messenger substances can enter the bloodstream and trigger inflammation in the brain. Chronically elevated cytokine levels are directly linked to depression, anxiety disorders, Alzheimer's disease and Parkinson's disease.
The blood-brain barrier - when the immune system attacks the brain
The blood-brain barrier (BBB) protects the brain from harmful substances - but an impaired immune response can make it more permeable. Immune cells and inflammatory substances can thus penetrate the brain and damage nerve cells there. This is suspected to be involved in the development of neurodegenerative diseases such as Alzheimer's and multiple sclerosis (MS).
How can you calm your immune system via the gut?
When an overactive immune response attacks the brain, the best strategy is to rebalance the immune system through stable gut flora and anti-inflammatory measures.
Strengthening the intestinal barrier
Fibre (prebiotics) from vegetables, pulses and wholegrains promote healthy gut bacteria and protect the intestinal mucosa. Glutamine & amp;Zincrepair damaged tight junctions and reduce intestinal permeability.
Entzündungsreaktionen senken
Omega-3 fatty acids (fish, linseed, algae) have a strong anti-inflammatory effect. Polyphenols - a subgroup ofsecondary plant substances(berries, green tea, turmeric, dark chocolate) reduce the production of IL-6 and TNF-α.
Probiotics& amp; fermented foods (sauerkraut, yoghurt, kimchi) promote anti-inflammatory intestinal bacteria.
Immune modulation by the vagus nerve
Breathing exercises, meditation and exposure to cold activate the "cholinergic anti-inflammatory reflex", which systematically reduces inflammation.The vagus nerve regulates the release of anti-inflammatory messenger substances and has a direct effect on the immune system.
Conclusion - Gut-brain axis
The gut-brain axis is an exciting field of research that goes far beyond digestion - it influences our immune system, mood and mental performance. New insights into the microbiome and innovative approaches such as personalized nutrition and vagus nerve stimulation could open up new ways to promote health in the future.
Some things still remain unclear, however, and science is only just beginning to fully understand the complex mechanisms involved. What is already clear is that a healthy gut contributes far more to well-being than has long been assumed - and could be a key to new prevention and treatment options.
