How the gut microbiome affects your mood and stress levels: The invisible connection between the gut and the brain

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Stress makes our stomach hurt. When we are in love, we feel "butterflies in our stomach". Before an important event, we feel nauseous, and when something worries us, we feel heaviness in our stomach. All these everyday sensations are direct evidence that our mind and emotions are inextricably linked to our intestines. For a long time, science believed that mood, anxiety, and depression were formed exclusively in the brain. However, modern biomedical discoveries have made a real revolution: the center of our mental health is in the intestines, and it is controlled by trillions of bacteria - our microbiome.

From an evolutionary perspective, our brains could never have existed without the constant input from our gut. Today, it has been proven that complex conditions such as depression, anxiety, post-traumatic stress disorder (PTSD), autism, and even Parkinson's and Alzheimer's diseases are directly linked to the state of our gut microbiota.

The Gut-Brain Axis: The Main Highway of Emotions

How exactly do the bacteria that live in our gut dictate how we feel? The answer lies in what's called the gut-brain axis, a complex two-way communication system that connects the central nervous system with the enteric nervous system.

The main "cable" of this connection is the vagus nerve (Nervus vagus) . Interestingly, about 90% of the signals along this nerve go from the intestines to the brain, and not vice versa. That is, our stomach constantly "reports" to the brain about the situation in the body. Microbiota modulates the activity of the amygdala of the brain - a key structure responsible for feelings of fear, anxiety and mood regulation.

Bacteria as neurotransmitter factories

For a long time, it was believed that the hormones of joy and peace were synthesized exclusively by the neurons of the brain. However, the microbiome turned out to be a real chemical laboratory.

Bacteria are capable of producing a huge number of substances that directly affect the brain:

Serotonin: Nearly 90% of serotonin (a hormone that regulates mood, emotional stability, and sleep) is synthesized in the gut. Serotonin deficiency is a major cause of clinical depression. A healthy microbiome supports its stable production, which helps us feel happy and calm.
GABA (Gamma-Aminobutyric Acid): This is the main inhibitory neurotransmitter in our nervous system. Certain types of bacteria, including Bifidobacterium and Lactobacillus (e.g. L. reuteri ), directly produce GABA, which helps to reduce nervous system activity, relieve tension, and promote deep sleep.
Dopamine and short-chain fatty acids (SCFAs): Beneficial bacteria ferment fiber to produce SCFAs (such as butyrate). These compounds not only nourish intestinal cells, but also cross the blood-brain barrier, affecting neuroplasticity and reducing neuroinflammation. In addition, microbes are involved in the production of dopamine, a hormone of motivation and reward.

Animal studies clearly demonstrate this power. When scientists bred mice completely devoid of their gut microbiota, their behavior was abnormal: they became extremely fearful, depressed, and showed signs of autism. But once their guts were colonized with bacteria from healthy donors, the animals lost their fear, began to socialize, and their anxiety disappeared.

How stress disrupts digestion: an evolutionary mechanism

The gut-brain connection is two-way. Not only do bacteria affect stress, but stress also has a devastating effect on bacteria.

Renowned neuroscientist Robert Sapolsky explains this by evolutionary mechanisms. When you experience acute stress (for example, before a public performance or when faced with danger), your body goes into "fight or flight" mode. At this moment, the body accumulates all the resources to save life. The mouth dries up, saliva stops being produced - and this is the first step towards a complete shutdown of the entire gastrointestinal tract.

The body decides, "If I'm trying not to become someone's lunch, I don't feel like digesting my own breakfast right now ." Digestion slows down or stops.

When stress lasts for two minutes, it’s not scary. But in the modern world, people live in a state of chronic stress. Chronic shutdown of the digestive system leads to serious gastrointestinal disorders. Moreover, stress hormones (cortisol and adrenaline) directly affect the composition of the microbiota: beneficial bacteria die, and pathogenic microorganisms in the presence of stress hormones begin to multiply much faster.

Inflammation and depression: a vicious cycle

Chronic stress and poor diet (particularly excess sugar and ultra-processed foods) can compromise the integrity of the intestinal wall, allowing bacterial toxins to enter the bloodstream, causing low-level systemic inflammation.

Recent studies prove that it is precisely the inflammatory processes caused by stress and dysbiosis that can worsen or even trigger depression . The body is in a state of constant struggle. If we lose valuable bacteria that produce serotonin and GABA, our mood drops, anxiety increases, we sleep worse, which again increases stress. A vicious circle arises. In addition, microbes are able to control our eating behavior: those microorganisms that "love" sweets will send signals to the brain via the vagus nerve, forcing us to "eat up" stress with sweets.

Psychobiotics and Pharmabiotics: Treating Emotions Through the Stomach

Conventional medicine often suggests antidepressants or tranquilizers that only work on the brain. However, if the cause is dysbiosis, treating symptoms without restoring the microbiome may be ineffective or temporary.

Today, psychobiotics and pharmabiotics are at the forefront of 4P medicine (personalized, predictive, preventive) . These are special strains of live bacteria that have been clinically proven to improve mental health.

A striking example is the development of an innovative pharmabiotic " Metabolic Antistress " , created on the basis of the author's strain Lactobacillus plantarum IMV B-7414. The action of this drug specifically works with the "gut-brain" axis. Its intake contributes to:

Reducing anxiety and irritability (by stimulating the synthesis of GABA and serotonin).
Improving sleep quality and restoring natural biorhythms.
Reducing cortisol levels (stress hormone) and reducing inflammation in the body.

In addition, deep genetic sequencing of the gut microbiome is being used to identify specific "culprits" of anxiety and develop a personalized nutrition plan. By changing our diet, we change our bacteria, and the bacteria, in turn, change our mood.

Conclusions

We are not only our own cells, but also the trillions of bacteria that live inside us. Our emotional state, resilience to life's challenges, quality of sleep, and ability to enjoy life directly depend on the microbial balance in the intestines. Understanding that stress destroys the microbiome, and a healthy microbiome can protect us from stress, we gain a powerful tool for managing our own lives. Taking care of our digestion with a balanced diet and evidence-based pharmabiotics is the most effective step towards a strong nervous system and a happy life.

Short questions and answers on the topic (Q&A)

1. How exactly do gut bacteria affect my mood?

Answer: Gut bacteria communicate with the brain through the vagus nerve. They synthesize or stimulate the production of about 90% of serotonin (the "happiness hormone") and GABA, a neurotransmitter that relaxes the nervous system, relieves tension and promotes good sleep. When there are few good bacteria, the levels of these substances fall, and we feel anxious and sad.

2. Why do digestive problems occur during times of severe stress?

Answer: During stress, the body activates an ancient evolutionary “fight or flight” mode, preparing to save its life. At this point, salivation stops, and all processes of digestion and tissue repair come to a sudden halt because they require too much energy. Chronic stress causes the intestines to “shut down” permanently, which causes bloating, cramps, and the death of beneficial bacteria.

3. What are psychobiotics (or pharmabiotics for stress)?

Answer: These are new generation biologics containing specific, clinically tested strains of live microorganisms (e.g. Lactobacillus plantarum IMV B-7414). They are able to specifically act on the gut-brain axis, reducing the level of the stress hormone (cortisol), eliminating systemic inflammation and physiologically suppressing anxiety and insomnia.

4. Can changing your diet cure depression and anxiety?

Answer: Nutrition plays a critical role. Ultra-processed foods and sugar feed pathogenic flora that causes inflammation that spreads to the brain and provokes depressive states. The introduction of fiber and proper personalized nutrition feeds beneficial bacteria that restore the synthesis of neurotransmitters of joy, which is a powerful tool in the comprehensive treatment of anxiety and depression.