How gut health affects mental well-being

The gut influences mental health via the gut-brain axis, which enables communication between the gut and the brain. The microbiome in the gut produces neurotransmitters (chemical messengers) that regulate our mood, emotions, cognitive functions, and feelings of hunger and fullness. Approximately 27.8% of adults in Germany suffer from a mental illness, meaning nearly one in four people are affected. The most common mental disorders include anxiety, depression, and problems related to alcohol or drug use (dgppn, 2024). Against this backdrop, the role of gut health in mental well-being is gaining increasing attention. The gut and brain are in constant communication and regulate many functions, including mood (Cleveland Clinic, 2023). Essential to this is the gut microbiome—the community of bacteria, viruses, and fungi in the gut. This article explores what the gut microbiome is and the role it plays in mental health.

Table of Contents

• What is the gut microbiome?
• Functions of the gut microbiota
• What exactly is the gut-brain axis?
• Does the gut microbiota influence mental health?
• What are signs of an imbalance in the gut microbiota?
• What can improve gut microbiota to support mental health?
• Summary

What is the gut microbiome?

The “microbiome” refers to the entirety of microorganisms—including bacteria, viruses, fungi, and other microbes—that live in and on the human body, as well as their genes. It exists in various parts of the body, such as the skin, mouth, vagina, and gut. The term “microbiota,” which is used throughout this blog, refers specifically to the collection of microorganisms in a given habitat—for example, in the gut.

The microbiome is especially concentrated in the gut, where 95–99% of all microorganisms are found—equating to an estimated 100 trillion microbes. In adults, the gut microbiota is estimated to weigh between 1 and 2 kilograms (Thursby & Juge, 2017). Each person has a unique microbiota, which begins to develop at birth. Newborns acquire their first microbes during childbirth or through breastfeeding. Over time, the composition of the microbiome is influenced by various factors, including environment, diet, and lifestyle (Cleveland Clinic, 2023). The term “gut flora” is outdated and has been replaced by “microbiome.”

Functions of the gut microbiota

The idea of having countless bacteria in the body might seem unsettling at first. However, it is important to understand that a healthy gut microbiota typically consists of a diverse population of bacterial species—up to 300 to 1,000 different types (Thursby & Juge, 2017). These bacteria perform crucial functions:

Sources: Cleveland Clinic, 2023; NHS, 2023

The functions of the gut microbiota go far beyond digestion and are essential to overall health—not only by aiding digestion and nutrient absorption, but also by influencing mood and emotional balance through neurotransmitter production. To perform all of these roles, the gut and brain are in constant communication via what is known as the gut-brain axis.

What exactly is the gut-brain axis?

The gut-brain axis describes the bidirectional communication between our gut microbiota and our brain. It acts as a feedback system in which information is continuously exchanged between the gut and the brain, integrating signals from other areas of the body as well, such as the immune and endocrine systems.

Communication between the gut and brain occurs in several ways. Neurotransmitters produced by microbes in the gut can directly reach the brain and exert their effects. Additionally, gut microbes activate immune cells, which then send signals to the brain to help regulate inflammatory responses. The vagus nerve also transmits signals between the gut and the brain. Furthermore, metabolic byproducts of the microbes—such as short-chain fatty acids—can influence brain function by traveling through the bloodstream to the brain. One such example is butyrate, which has anti-inflammatory effects in the brain and contributes to the regulation of brain function and support of cognitive health (Refisch & Walter, 2023, Cleveland Clinic, 2023).

The table shows the various processes that are regulated by the communication between the gut microbiota and the brain, as well as the effects that can occur when the balance of this communication is disturbed, for example by a dysbiosis, i.e. an imbalance of the gut microbes:

Source: Own illustration based on Refisch & Walter, 2023, Cleveland Clinic, 2023

Does the gut microbiota influence mental health?

Yes, the gut microbiota has a significant impact on our mental health. A dysbiosis in the gut is associated with various mental health disorders, including anxiety disorders, depression, bipolar disorder, and schizophrenia. Dysbiosis refers to an imbalance in the composition of microbes in the gut.

This leads to a shift between beneficial and harmful microorganisms. A healthy microbiota is characterized by a diverse population of microbes that exist in a balanced relationship. In dysbiosis, this diversity is reduced, and disease-causing microbes may dominate. This can impair the normal functioning of the microbiota and manifest in the following ways:

• Damage to the gut barrier: Dysbiosis can damage the gut barrier, leading to a “leaky gut,” where bacteria enter the bloodstream and trigger inflammation throughout the body. These inflammations are associated with various mental health disorders (Mhanna et al., 2023).

• Disruption of stress regulation: Dysbiosis can impair the regulation of stress responses, increasing susceptibility to stress-related disorders.

• Impaired neurotransmitter production: Dysbiosis can disrupt the production of neurotransmitters or their precursors, which are essential for mood regulation. Imbalances in these chemicals are linked to mental health conditions (Delanote et al., 2024).

• Lack of beneficial bacteria: Studies show that individuals with mental illnesses often have a reduced abundance of beneficial bacteria and lower microbial diversity. In people with depression, higher concentrations of inflammation-promoting bacteria have frequently been observed (Xiong et al., 2024).

These findings already suggest potential links between the gut microbiota and mental disorders, though further research is needed to confirm causal relationships. 

Want to assess your own gut health?

The above insights already suggest potential connections between gut microbiota and psychological disorders, yet more studies are needed to determine causality. Inflammation may play a key role in the development and worsening of mental illnesses. For this reason, it can be helpful to test for possible inflammation early—especially if you’re experiencing symptoms such as abdominal pain, diarrhea, or fatigue.

With Homed-IQ’s Gut Inflammation Test, you can conveniently check from home whether inflammation is present in your gut—or rule it out as a cause. The test measures the concentration of calprotectin in stool, a protein released during intestinal inflammation.

What are the signs of an imbalance in the gut microbiota?

Although research has not yet identified what an ideal gut microbiota looks like, it is already clear that it plays a crucial role in our overall health. For this reason, it’s important to recognize the signs of an imbalance—referred to as dysbiosis—so that steps can be taken early. Here are some signs to watch out for:

• Digestive issues such as frequent bloating, constipation, or diarrhea

• Skin problems such as acne, eczema, or other skin irritations

• Low energy, concentration difficulties, and persistent fatigue

• Frequent infections due to a weakened immune system

• Mood changes, such as sudden mood swings, anxiety, or depressive symptoms

• Changes in weight, including unintentional weight gain or loss

Source: Cleveland Clinic, 2024

What can improve gut microbiota to support mental health?

Below are some proven strategies to improve your gut microbiota and gut health. These tips not only help maintain a healthy microbiota but also support your overall physical and mental well-being through balanced nutrition and effective stress management.

Sources: Harvard Health, 2021; Cleveland Clinic, 2024

Summary

The gut influences mental health through the gut-brain axis, which enables bidirectional communication between the gut microbiota and the brain. The gut microbiota produces important neurotransmitters that regulate mood, emotions, and cognitive functions. Dysbiosis—an imbalance of gut microbes—is associated with mental health disorders such as anxiety and depression. Measures to support gut microbiota, including the intake of probiotics and prebiotics, a fiber-rich diet, stress reduction, and avoiding unnecessary antibiotics, can help maintain microbial balance and promote mental well-being.