Our body contains more than 10 000 different species of bacteria that live in our gut, but what does this mean and why is this so important?
Ok, so let’s start but defining what the microbiome actually is – your gut is inhabited by an array of microorganisms or bacteria that basically create a mini-ecosystem in your body. While we often associate bacteria with infection and disease, the bacteria living inside your stomach is actually healthy and good for you (or should be most the time) and is essential for life as we rely on them for many different functions.
Our microbiome helps us to:
– Digest food
– Create vitamins
– Assists in regulating our immune system
– Protects us from bad bacteria that is associated with disease
In more recent times, what is in our gut has been strongly associated with the way we feel and even behave through what is now known as the “gut-brain axis”. We now know this occurs as the bacteria in our gut is linked to the chemicals in our brain, that are responsible for our brain’s communication. These chemicals are known as neurotransmitters. Neurotransmitters are responsible for regulating a lot of our body’s physiological responses including mood, emotions, stress, appetite and everything in between.
The vagus nerve has been described as “superhighway of connectivity between your gut and brain” that facilitates communication within the gut-brain axis. It plays a vital role in many of the body’s physiological functions; monitoring heart rate, stress and anxiety, influencing swallowing and digestion, and has even been related to memory. When someone is calm and collected, the vagus nerve is activated leading to normal digestive functioning, a calmer heart rate is maintained, and in turn you have better sleep, improved memory and immune function. Unsurprisingly, the vagus nerve has been associated with greater levels of ‘good bacteria’ and lower levels of inflammation.
Less diversity in our gut bacteria or higher levels of bad bacteria has been directly linked to lower levels of serotonin and GABA, which both directly affect the way we feel. Serotonin is known to be a key player in the role of feelings of positivity and well-being. What’s more, it acts as a precursor to another chemical called melatonin – melatonin is responsible for regulating our circadian rhythms and body clock – so you can see how serotonin affects sleep as well. Studies on depression have also consistently reported lower levels of serotonin found in patients with depression. GABA (aka gamma-Aminobutyric acid) is the chief neurotransmitter in charge of inhibiting feelings of anxiety and therefore increasing feelings of calmness.
Research has also shown that our microbiome’s diversity can also be linked to cognitive decline and mood disorders such as depression, through inflammation. When the variety our gut species is lower, research has found that there is an increase of cytokines. So what is a cytokine? Good question! The term cytokine refers to a broad group of proteins that our bodies’ produce to regulate the nature and duration of our immune system’s response to fighting off disease. They are helpful in the removal of damaged cells and promote healing. While cytokines have an adaptive function and assist our body in maintaining an equilibrium (known as homeostasis), if they are functioning too frequently this results in chronic inflammation. While the mechanisms that link inflammation to cognitive decline are still being investigated, the current landscape of research reports that the link between cognitive decline and inflammation is strong. This is further evidenced as chronic inflammation has been associated with more adverse outcomes, such as increased levels of neuropsychiatric disorders like depression and Alzheimer’s Disease.
The gut-brain axis does not only talk from our gut to our brain but is evidently bidiectional. The brain can influence what species are predominant in our gut through:
a) choosing what substances are allowed into our blood stream from our gut and what substances should not be allowed through. It does this through altering the leakiness (or permeability) of the gut lining.
b) secreting chemicals that alter the gut’s environment to be more favourable for certain strains of bacteria to flourish, while reducing the likelihood of other bacteria colonies to be present.
Funnily enough, the brain’s influence over the microbiome is further evidenced by the fact that when the brain’s stress and anxiety levels increase, there is an increase in ‘bad bacteria’. Similarly, a calmer state has been linked to increasing levels of ‘good bacteria’. Research has even been able to distinguish patients diagnosed with major depressive disorder from healthy controls just through analysis of their microbiota.
Click on the link below to find out ways in which you can improve your overall gut health to boost brain performance.
Cryan, J. F., & O’mahony, S. M. (2011). The microbiome‐gut‐brain axis: from bowel to behavior. Neurogastroenterology & Motility, 23(3), 187-192.
Godbout, J. P., & Johnson, R. W. (2009). Age and neuroinflammation: a lifetime of psychoneuroimmune consequences. Immunology and allergy clinics of North America, 29(2), 321-337.
Jiang, H., Ling, Z., Zhang, Y., Mao, H., Ma, Z., Yin, Y., … & Li, L. (2015). Altered fecal microbiota composition in patients with major depressive disorder. Brain, behavior, and immunity, 48, 186-194.
Lima-Ojeda, J. M., Rupprecht, R., & Baghai, T. C. (2017). I Am I and My Bacterial Circumstances: Linking gut microbiome, neurodevelopment, and depression. Frontiers in psychiatry, 8, 153.