The interactions between the gut and the 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.

Hard to believe, but while the brain has about 86 billion neurons, the intestine with its enteric nervous system (ENS) – consisting of around 100 million nerve cells – is similarly complex. This nervous system operates largely autonomous, controls digestion, processes signals and mediates reflexes. However, it also continuously interacts with the central nervous system (CNS), which underlines the importance of the intestine as "second brain" underlines.

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 area of ​​research that is already much better researched than it was ten years ago. However, it is still largely considered a "black box" and we can expect many more exciting findings from research into this compound, which have the potential to change both basic medicine and therapeutic approaches.

Which components play a role in the gut-brain axis?

To start with, this overview should give you an idea of ​​which parts of our body are connected in the gut-brain axis and therefore influence each other. A whole orchestra of processes is formed that work together here and if one of them is not playing in time, it can affect the entire piece. In the rest of the text, we will go into more detail about the individual players.

Neural Communication

• The vagus nerve is the most important direct connection between the gut and the brain. It transmits signals in both directions and influences, among other things, digestion, emotions and stress levels.
• The enteric nervous system, also called the “gut brain,” independently regulates many functions of the gastrointestinal tract.

microbiome and metabolites

• The trillions of microorganisms in the intestine (microbiome) produce neurotransmitters such as serotonin, dopamine and GABA, which can directly affect the brain.
• Short-chain fatty acids such as butyrate, propionate and acetate have immunomodulatory and neuroprotective effects.

Endocrine (hormonal) communication

• The intestine produces hormones such as ghrelin, leptin and peptide YY, which Appetite, mood and metabolism influence.
• The hypothalamic-pituitary-adrenal axis (HPA axis) reacts to stress and can be inflammations or intestinal dysbiosis be influenced.

Immunological Interaction

• The intestine contains about 70% of the immune system.
• A disrupted intestinal barrier (leaky gut) can trigger inflammatory processes that are associated with neurological and mental illnesses.

The vagus nerve as the main connection

The vagus 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 and intestines. In the past, the vagus nerve was mainly researched in neurology and cardiology, but today it is becoming increasingly clear that it is not only responsible for controlling the organs, but also our mood, our immune system and even chronic inflammation It is therefore no wonder that the vagus nerve is currently gaining enormous attention – both in science and in the media.

How does the vagus nerve affect the intestines?

The vagus nerve is the direct communication route between the gut and the brainIts 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 movement

The vagus nerve controls the mobility of the intestine by 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) lead.

anti-inflammatory and immune system

It activates the cholinergic anti-inflammatory reflex, a body's own protective system against inflammationsIf this mechanism is disturbed, chronic inflammation can occur, which can be seen in Crohn's disease, ulcerative colitis or autoimmune diseases play a role.

influence on mood and the nervous system

The vagus nerve influences the production of neurotransmitters How serotonin, dopamine and GABAthat are important for our mood and mental performance. Disturbed vagal activity is associated with Depression, anxiety disorders and even neurodegenerative diseases such as Parkinson's associated with.

communication with the microbiome

Intestinal bacteria produce substances that are transmitted to the brain via the vagus nerve. Dysbiosis (imbalance in the microbiota) can be used to cognitive and emotional disorders lead. dysbiosis is also one of the 12 signs of aging.

TENS training is also a variant of neuromodulation that works in a similar way to vagus nerve stimulation. However, with vagus nerve stimulation, the electrodes are more likely 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 physical processes, researchers have been working intensively on possible forms of therapy. Some of these have already been officially approved or are being clinically tested. This field is also referred to 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. The nerve is stimulated by electrical impulses – either via an implanted device or via a non-invasive method (e.g. via the ear region). This therapy is used for:

• epilepsy
• Treatment-resistant depression
• cluster headaches
• (Researched for) Irritable Bowel Syndrome & Chronic Inflammation

Polyvagal Therapy (Stephen Porges' Polyvagal Theory)

Focuses on the activation of the “ventral vagus” for Reduction of anxiety, trauma and digestive disorders. Applied Techniques are Breathing exercises, meditation, physical exercises and pressure points.

Natural Methods for Vagus Nerve Stimulation

• Deep breathing: Longer exhalation activates the parasympathetic nerve.
• Cold exposure: Contrast showers or ice water baths increase vagal activity. Extreme sports enthusiasts in particular Wim Hof 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: Chronic stress and burnout are increasing worldwide, and the vagus nerve offers a natural way to calm the nervous system.

• New findings on the treatment of chronic inflammation: Studies show that low vagal activity is associated with silent inflammation (low-grade inflammation, or Inflammaging), which play a role in autoimmune diseases, diabetes and cardiovascular diseases.

• Trend in self-optimization & biohacking-Scene: DThe vagus nerve is celebrated as a “super nerve” – and methods such as breathing techniques, cold baths and vagus-activating diet and exercises have become popular trends.

The Role of the Gut Microbiome

The intestinal microbiome as a key player in the gut-brain axis

The intestinal microbiome - the trillions of bacteria, viruses and fungi that live in our intestines have a direct influence on the communication between the gut and the brain.These microorganisms produce a variety of neurotransmitters, hormones and metabolites, which are about the vagus nerve, the immune system and the endocrine system communicate with the brain.

Healthy microbiota promote mental well-being, while a dysbiosis is associated with mental and neurological diseases - which means 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 flatulence, diarrhea and nutrient deficiencies. Which substances are produced in the intestine, what do they influence and which bacteria play a special role? We will now take a closer look at these questions.

What substances are produced by the microbiome that are involved in gut-brain communication?

The communication between the gut and the brain takes place via three main mechanisms:

1) Production of neurotransmitters and neuromodulators

Certain intestinal bacteria produce directly neurotransmittersthat play a central role in our mood, cognition and intestinal motility. These include:

serotonin (5-HT) – "happiness hormone"

• 90% of serotonin in the body are produced by enterochromaffin cells in the intestine, which are regulated by intestinal bacteria.
• Producing bacteria: Escherichia coli, Enterococcus, Streptococcus, Lactobacillus and Bifidobacterium.
• Function: Regulates mood, Sleep, appetite and bowel movements.
• Dysbiosis effects: A serotonin deficiency can be associated with depression, anxiety disorders and irritable bowel syndrome (IBS).

Dopamine - "motivation hormone"

• 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 – "relaxation hormone"

• 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 by Faecalibacterium 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 binfluence energy metabolism in the brain.

3) Modulation of the immune system and inflammatory responses

The microbiome regulates the immune system through certain substances and influences the blood-brain barrier and inflammatory processes:

lipopolysaccharides (LPS) (from gram-negative bacteria such as Enterobacter and Escherichia coli)

• Can damage the intestinal barrier (“leaky gut”) and trigger inflammation throughout the body.
• Dysbiosis effects: Chronic inflammation caused by LPS is associated with depression, anxiety disorders, Parkinson's and Alzheimer's.

tryptophan metabolites (e.g. indole, kynurenine)

• Determine whether tryptophan is broken down into serotonin (good) or neurotoxic kynurenines (bad).
• Imbalanced tryptophan metabolism is associated with sleep disorders, depression and cognitive impairment

Hormones and Neurotransmitters: The Biochemical Language of the Gut

The intestine 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. About the gut-brain axis These hormones communicate directly with the brain and influence our behavior and physiological processes throughout the body.

hunger and satiety hormones

The intestine plays a crucial role in regulating appetite:

Ghrelin – the hunger hormone

• Produced in the stomach and small intestine, ghrelin increases appetite by signaling to the brain that it is time to eat.
• Sa level rises before a meal and falls after food intake.

Peptide YY (PYY) – the satiety hormone

• It is secreted in the lower small intestine and upper large intestine and signals to the brain that sufficient food has been consumed.
• 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 blood sugar levels is lowered.
• Slows down gastric emptying and thus ensures a longer lasting feeling of satiety.
• Due to its effects, 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 the feeling of satiety.

digestive regulating hormones

In addition to controlling appetite, the intestine also regulates numerous digestive processes:

gastrin sstimulates stomach acid production to promote the digestion of proteins.

secretary wIs released in the small intestine upon contact with acidic stomach contents and causes the pancreas to produce bicarbonate to neutralize stomach acid.

Motilin rregulates the so-called Migrating Motor Complexes (MMC), rhythmic contractions that occur between meals and clean the intestines. This function is currently the focus of research and plays a special role in colonization and irritable bowel syndrome.

Neuroactive hormones

The close connection between the gut and the brain is mediated by a number of neuroactive hormones:

Serotonin – the happiness hormone

• Approximately 90% of the total serotonin are not produced in the brain but in the intestine.
• It controls intestinal motility, but also influences the central nervous system and thus mood.
• Impaired serotonin production is associated with irritable bowel syndrome, depression and anxiety disorders.

cortisol (indirectly influenced by intestinal bacteria)

• Although cortisol produced in the adrenal glands, the gut microbiome indirectly controls the stress response via the HPA axis, neurotransmitters and the immune systemA healthy gut flora can help cushion cortisol spikes, reduce inflammation and increase stress resistance – an important key to mental and physical balance.

The immune system and the communication between the gut and the brain

Around 70% of all immune cells are located in the intestine, where they work in a highly sensitive interaction with the microbiome.If this balance is disturbed, it can have fatal consequences: inflammatory substances from the intestine enter the blood and directly affect the brain

But how exactly does the immune system affect the gut-brain axis? And how can you specifically reduce inflammation to protect not only the gut but also the brain?

The intestinal barrier – your immune defense on the front line

The intestinal mucosa is the first layer of protection against unwanted invaders. It decides which substances are allowed to enter the blood.

tight junctions are tiny proteins that hold the intestinal cells together like a barrier – but in the event of inflammation or dysbiosis they can become permeable.

"leaky gut" occurs when toxins, undigested food particles or bacterial components (e.g. lipopolysaccharides, LPS) through the intestinal wall into the blood and cause trigger immune reaction.

Inflammation as a silent threat to the brain

If the immune system becomes unbalanced, it releases pro-inflammatory cytokines:

• interleukin-6
• tumor necrosis factor-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 and Parkinson's.

The blood-brain barrier – when the immune system attacks the brain

The blood-brain barrier (BBB) protects the brain from harmful substances – but a disturbed immune response can make it more permeable. Immune cells and inflammatory substances can 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 through the gut?

When an overactive immune response attacks the brain, the best strategy is to rebalance the immune system through stable intestinal flora and anti-inflammatory measures.

Strengthening the intestinal barrier

fiber (prebiotics) from vegetables, legumes and whole grains promote healthy intestinal bacteria and protect the intestinal mucosa. glutamine & zinc repair damaged tight junctions and reduce intestinal permeability.

reduce inflammatory reactions

omega-3 fatty acids (fish, linseed, algae) have strong anti-inflammatory effects. Polyphenols – a subgroup secondary plant substances (Berries, green tea, turmeric, dark chocolate) reduce the production of IL-6 and TNF-α.

Probiotics & fermented foods (sauerkraut, yoghurt, kimchi) promote anti-inflammatory intestinal bacteria.

Immune modulation through the vagus nerve

breathing exercises, meditation and cold exposure activate the “cholinergic anti-inflammatory reflex”, which systematically reduces inflammation. The vagus nerve regulates the release of anti-inflammatory messenger substances and acts directly 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, our 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.

However, some things still remain unclear, and science is only relatively early in its journey to fully understanding the complex mechanisms. What is already certain is that a healthy gut contributes far more to well-being than was long assumed - and could be a key to new prevention and treatment options.