The microbiome refers to the entire collection of genes from all the microbes (bacteria, fungi, protozoa and viruses) that live on and in our body. These microbes perform mainly symbiotic functions, which means that our bodies benefit from their presence (and they benefit from our bodies). The functioning of our microbiome reflects our state of health, both physically and mentally. Our largest microbiome (in terms of numbers) exists in our large intestine, and helps to process food and liquid intake to create optimal bodily function.
The gut microbiome
Our intestines are inhabited by trillions of microbes. We need them for the digestion of food. For instance, complex carbohydrates and fibres can only be digested through fermentation processes of certain bacteria. What’s more, through this fermentation the bacteria create substances such as short-chain fatty acids, which are essential for many bodily functions, including our brain and mental health.
Communication between the gut and the brain
The above is only one example of how the gut microbiome can influence the brain. The gut and the brain are in continual communication to monitor and stabilize body functions. There are several routes through which the gut and the brain can interact. First, the vagus nerve forms a direct connection. Many of our para-sympathetic nerve responses (breathing, heart rate, inflammation, relaxation) are triggered via vagus nerve communications. Second is through the immune system, which interacts with the microbes in the gut. The immune system thus has to learn which microbes are good and which ones to attack. When early in life the gut microbiome does not develop well, this might lead to auto-immune diseases such as eczema and asthma, although such causal effects do still need to be confirmed by research. The third route is through the blood system. As mentioned, microbes in the gut produce many substances such as short-chain fatty acids, amino acids, vitamins, and hormones. From the gut these move through our bodies and also into our brains, where they are important for many cognitive functions.
Gut microbes live mainly from the food we eat. Therefore, by eating healthy, you will also take good care of your gut microbiome. For instance, eating whole wheat products and vegetables will make the good bacteria in your gut very happy! On the other side, unhealthy foods can cause inflammation, triggering responses from the immune system that can be harmful for your mental health. What’s more, these types of foods can also stimulate the growth of bad bacteria in your gut, that compete with the ones that are good for you. As brain function is dependent on the chemicals produced in the gut, it’s important to have a well-functioning gut microbiome.
Stress and tobacco smoke can also be harmful for the gut microbiome, while physical exercise can stimulate your healthy gut bacteria. A healthy lifestyle will therefore contribute to a well-functioning gut microbiome, which is important to keep your brain healthy.
In the research of Eat2beNICE we are studying the link between diet, the gut microbiome, brain functioning and mental health. We expect that changes in the gut microbiome, in response to changes in diet, can predict or explain changes in brain functioning and behaviour. Probiotics for instance are food substances with live bacteria, that benefit the functioning of the gut microbiome. We are studying if treatment with probiotics can be helpful in improving mental health.
Cryan et al. 2019 The Microbiota-Gut-Brain Axis. Physicology Reviews, 99(4) https://www.ncbi.nlm.nih.gov/pubmed/3146083
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