Author: Astrid Vincze | Editor: Laure Pauly, Anja Leist
“Tell me what you eat, and I will tell you what you are” was written in 1825 by the French gastronome Jean Anthelme Brillat-Savarin in his book Physiology of Taste. At the time, no one knew that trillions of microorganisms live inside our digestive system that are partly fed by what food we consume and that help us metabolize it. Today we know that these microbes, collectively called the gut microbiome, have a surprisingly close relationship with our brain, influencing how we feel, think, and respond to the world (1)
Communication between the gut and the brain happens through what scientists call the gut–brain axis. Through this system (using nerves such as the vagus nerve, immune signals, and molecules circulating in the blood) gut-derived compounds can influence brain function and behavior (2). Many of these signals are closely linked to mood and emotions.
Your brain is continuously affected by your gut microbiome. What you eat shapes which microbes thrive in your intestines, and these microbes produce or regulate a wide range of molecules that can communicate with the brain.
Tiny molecules from the gut, big effects on the brain
The gut microbiome is made up of trillions of tiny living microorganisms, including bacteria. These microorganisms produce or help control many molecules that affect the brain. For example, the gut microbiome makes most of the body’s serotonin, influences how dopamine is processed, and can even produce the neurotransmitter GABA. All of these chemicals are important for mood, stress, and thinking. About 90% of the body’s serotonin, which affects mood, appetite, and sleep, comes from the gut (3).
Some bacteria in the microbiome, like Enterococcus and Lactobacillus, can change how dopamine, the “feel-good” chemical, is used in the body (4).
Some gut microbes can also make GABA, the brain’s main calming chemical. GABA helps reduce stress and anxiety. Signals from these microbes can influence the nervous system and the body’s stress responses.
Gut microbes also make short-chain fatty acids, like butyrate, when they break down fiber from food. Butyrate helps keep the gut lining healthy, reduces inflammation, and can travel in the blood to help the brain (5). In the brain, it supports nerve cells and may help with learning, memory, and mood.
The microbiome also affects tryptophan, an amino acid that can be turned into serotonin or other compounds that influence inflammation and brain signals.
In short, the gut microbiome plays a big role in controlling important brain chemicals such as serotonin, dopamine, and GABA. Because diet affects which microbes grow in the gut, what we eat directly changes the signals sent to the brain. Together, our food and gut microbes help shape our mood, stress levels, thinking, and overall brain health.
So what are these molecules involved in? The gut–brain axis influences many aspects of our mental well-being (6), among these:
- mood
- memory
- stress responses
- anxiety
Why this matters for health and brain health
We talk about dysbiosis when the balance of gut microbes, the affluence and composition of microscopic organisms living in our body, becomes disrupted. Such an imbalance can also affect the systems connected to the gut, including those involved in regulating mood, stress, and cognitive functions.
This can be associated with several health conditions, including depression, anxiety, brain fog, and is found in neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease (7, 8). In fact, people with certain mental health conditions often have gut microbiota profiles that differ from those of healthy individuals, and ongoing research is investigating these relationships better.
A two-way conversation: gut and brain
Importantly, the relationship goes both ways. The brain influences the gut, and the gut influences the brain, forming a continuous feedback loop that is critical for both mental and physical health. Molecules such as serotonin, GABA, dopamine, and butyrate are the chatter in this biochemical conversation between microbes and the nervous system, shaping mood, hormonal responses, and overall well-being.
Simple ways for a healthier gut and brain
The good news is that we can change our microbiome with our daily habits. Eating foods rich in fiber, eating fermented foods, drinking enough water, and having a balanced diet can help keep our gut healthy and diverse. This helps the communication between our gut and brain and can affect how we feel, think, and react.
Fermented dairy products such as yogurt and kefir are interesting in this context. They contain live bacteria that can support a healthy gut. Some scientific reviews show that fermented foods, including dairy, may have small positive effects on the gut–brain connection. They may also help with mood and stress (9, 10).
However, dairy is not the same for everyone. Some people do not tolerate it well or choose not to eat it. The main message is that dairy is not simply good or bad. Fermented dairy, in particular, can be an important part of a healthy diet if it suits you.
Two hundred years after Jean Anthelme Brillat-Savarin wrote “Tell me what you eat, and I will tell you what you are,” science shows that this idea is very true. What we eat does not only feed our body, it also feeds the many microbes living inside us. These microbes help control our mood, our thoughts, and how we deal with stress. In this way, we are not only what we eat, but also what our microbes do with it.
So at your next meal, remember that you are not only feeding yourself: you are also feeding trillions of microbes that can shape how you feel and even how you think.
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Astrid Vincze is a PhD student at the University of Luxembourg, working on the fascinating microbial world. Her research focuses on improving our ability to detect features in the microbiome that enable microorganisms to survive various environmental threats. She is also interested in the brain and its plasticity, and in how these two worlds intersect.
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For better readability of the text, the assistance of Microsoft Copilot, an AI language model based on the GPT-4 architecture, secured with UL enterprise data protection, has been used.
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