Gut-Brain Axis: The Influence of the Microbiome on Mental Health and Behavior
Content
1. What is the gut microbiome?
2. Gut-Brain Axis
3. Microbiome and ADHD
3.1 What is ADHD?
3.2 How is the gut connected to ADHD?
4. Microbiome and Depression
4.1 What is Depression?
4.2 How is the gut connected to Depression?
5. Summary
1. What is the gut microbiome?
The gut microbiome is a complex ecosystem consisting of trillions of bacteria, fungi, and other microorganisms that live in our digestive tract (1). These not only influence our immune system (2) but also communicate directly with the brain through the so-called gut-brain axis. They send signals via nerve connections, hormones (3), and immune signals, which can affect our mood and cognitive functions.
2. Gut-Brain Axis
In recent years, interest in the connection between our gut microbiome and mental health has been growing. Research shows that the gut flora plays an important role not only in digestion but also in our mood, concentration, and overall well-being:
The gut and brain are connected through a complex network of nerves, hormones, and signaling molecules known as the gut-brain axis. This network ensures that our digestive system and nervous system continuously exchange information. The gut microbiome plays a key role in this process: it can send signals to the brain via special molecules and nerve pathways, influencing our mood, behavior, and well-being. Conversely, stress, anxiety, and other psychological factors also directly affect the gut and digestion. Therefore, a healthy gut can have a positive impact on our mental health.
3. Microbiome and ADHD
3.1 What is ADHD?
ADHD stands for Attention Deficit/Hyperactivity Disorder and is a common mental health condition in children and adolescents that can persist into adulthood. ADHD is characterized by three main symptoms: excessive movement (hyperactivity), difficulty concentrating (inattention), and impulsive behavior. The severity of these symptoms can vary. Without proper support, ADHD can lead to difficulties in school, family conflicts, and other problems. (4) (4)
3.2 How is the gut connected to ADHD?
,Research shows that in ADHD, the composition of the gut microbiome is often altered (5). Some studies have found, for example, a lower diversity of certain beneficial bacteria in affected individuals (5). This may mean that important bacteria are missing; bacteria that influence neurotransmitters like dopamine and serotonin, which play a key role in attention, impulse control, and mood. At the same time, an altered microbiome can promote inflammatory processes that can also affect the brain.
Whether changes in the microbiome are a cause of ADHD, worsen symptoms, or do both is not yet fully understood. However, this suggests that a targeted healthy diet and support of the gut flora (e.g., through prebiotic and probiotic foods) could be promising approaches to help people with ADHD.
4. Microbiome and Depression
4.1 What is Depression?
Depression is a mental illness in which individuals experience prolonged periods of persistent sadness, lack of motivation, and a loss of joy and interest. It is often accompanied by additional symptoms such as concentration difficulties, sleep disturbances, changes in appetite, and reduced self-esteem. Depression is more than just temporary mood lows and can significantly affect daily life, work, and relationships. It arises from a combination of genetic, biological, psychological, and social factors and is generally treatable, for example through psychotherapy, medication, and support with managing daily life.
4.2 How is the gut connected to Depression?
The microbiome also plays an important role in depression. Gut bacteria produce key neurotransmitters like serotonin, which regulate our mood. An imbalance in the microbiome can also promote inflammation, which is linked to depressive symptoms. Studies show that people with depression often have an altered gut flora (6) and that probiotic supplements can help improve symptoms (7).
5. Summary
Recent research increasingly highlights the close connection between the gut and the brain. The microbiome plays a crucial role in regulating mood, concentration, and behavior, and can have a significant impact on both ADHD and depression. By adopting a targeted healthy diet and fostering a diverse gut flora, it is possible to create opportunities to support mental health. Understanding the gut-brain axis can thus help provide better support for people with ADHD and depression and open new paths to improving their quality of life.
If you want to learn more about how targeted nutritional strategies and modern microbiome tests can help restore balance in your gut, it’s best to consult a nutritionist or therapist. You can find experts trained through our SIBO Academy here.
References
- Sender R, Fuchs S, Milo R. Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS Biol. 2016 Aug 19;14(8):e1002533. doi: 10.1371/journal.pbio.1002533. PMID: 27541692; PMCID: PMC4991899.
- Hooper, L.V., Littman, D.R., and Macpherson, A.J. (2012). Interactions between the microbiota and the immune system. Science (New York, N.Y.) 336, 1268-1273. https://doi.org/10.1126/science.1223490.
- Clarke G, Stilling RM, Kennedy PJ, Stanton C, Cryan JF, Dinan TG. Minireview: Gut microbiota: the neglected endocrine organ. Mol Endocrinol. 2014 Aug;28(8):1221-38. doi: 10.1210/me.2014-1108. Epub 2014 Jun 3. PMID: 24892638; PMCID: PMC5414803.
- https://www.bundesgesundheitsministerium.de/themen/praevention/kindergesundheit/aufmerksamkeitsdefizitsyndrom.html; last checked 23.06.2025
- Prehn-Kristensen A, Zimmermann A, Tittmann L, Lieb W, Schreiber S, Baving L, Fischer A. Reduced microbiome alpha diversity in young patients with ADHD. PLoS One. 2018 Jul 12;13(7):e0200728. doi: 10.1371/journal.pone.0200728. PMID: 30001426; PMCID: PMC6042771.
- Valles-Colomer M, Falony G, Darzi Y, Tigchelaar EF, Wang J, Tito RY, Schiweck C, Kurilshikov A, Joossens M, Wijmenga C, Claes S, Van Oudenhove L, Zhernakova A, Vieira-Silva S, Raes J. The neuroactive potential of the human gut microbiota in quality of life and depression. Nat Microbiol. 2019 Apr;4(4):623-632. doi: 10.1038/s41564-018-0337-x. Epub 2019 Feb 4. PMID: 30718848.
- Huang R, Wang K, Hu J. Effect of Probiotics on Depression: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients. 2016 Aug 6;8(8):483. doi: 10.3390/nu8080483. PMID: 27509521; PMCID: PMC4997396.
