Microbiota and the Gut-Brain Axis in Mental and Physical Health

It sounds like something from a sci-fi movie… 

…mind control bacteria and microbes alter your thoughts. 

But that’s the exact finding of an impressive array of scientific papers. 

Believe it or not, the bacteria in your gut can influence brain development, brain chemistry, stress levels, perception and pain. According to neuroimmunologist John Bienenstock, MD, of McMaster University in Hamilton, Ontario.

The saying – “you are what you eat.” Or the famous quote by Hippocrates…

“Let food be thy medicine and medicine be thy food”

Your Second Brain | Microbes and Mind States

Why is your gut your second brain? The microbes in your gut and the functioning of your brain are intricately linked. Studies have shown that a slight tweak to the balance of microbes in the gut can alter your mood. Like the vast majority of scientific research, a lot of the studies carried out have been in rodent models. Researchers are continually trying to understand exactly how the microbiome shifts and what a healthy microbiome population looks like. 

The human gut has it’s own nervous system and neurons that work independently of the brain. Literally, the gut functions like a second brain. The bacteria that colonise our gut shift and change over time. At birth, the gut is (most probably) sterile and free from microbes. But immediately after or even during the birthing process, we begin to acclimate ourselves to the world around us. And the microbes in our gut provide essential information about our environment. 

How Exactly Does the Gut Microbiome Affect the Brain?

Gut microbes play a critical role in digestion and metabolism. Preferring prebiotic-rich foods as fuel – such as fruits, vegetables, nuts and legumes. The microbes in your gut take the food that you eat and break it down into nutrients that are essential for existence. Although these nutrients are critical for brain health and development, there is a second process that impacts your brain.

Neurochemicals are produced by microbes and can alter mood, learning and memory. One example of this is serotonin. Serotonin is the hormone responsible for levels of satisfaction and happiness. “Good” gut microbes are responsible for creating as much as 95% of the serotonin in your body. The type of microbes in your gut also alter the production of 

brain-derived neurotrophic factor (BDNF), a neurochemical that enhances memory and mood. 

In short – microbes are responsible for the gut-brain connection.

From Shyness/ Anxious to Bold and Adventurous

In one study, in a 2011 publication of Gastroenterology, researchers gave a timid and shy strain of mice (known as BALB/c mice) several antibiotics. Why? Because antibiotics (A.K.A antimicrobials) have long been known to significantly alter the gut microbiome. Interestingly, antibiotics altered the behaviour of shy mice, making them bolder and more adventurous. The antibiotics also altered brain chemistry by boosting levels of BDNF. Concluding that “intestinal dysbiosis might contribute to psychiatric disorders in patients with bowel disorders.”

In a second experiment from the same team, Bercik et. al studied shy BALB/c mice and courageous NIH Swiss mice. They got the gut microbes from one group of mice and did a full-scale microbial transplant. When the shy mice were colonised with gut microbes from the outgoing NIH Swiss mice, their behaviour significantly shifted. They became more adventurous and outgoing. Conversely,  when the adventurous NIH Swiss mice were colonised by the BALB/c mouse microbiome, they became more anxious and hesitant. 

How the Microbiome Influences Anxiety and Depression

Researchers have found that harmful bacteria can up-regulate anxiety, while “good bacteria” can boost confidence. In one study, published in the Proceedings of the National Academy of Sciences, researchers took two groups of mice. Feeding one group a broth containing the probiotic Lactobacillus rhamnosus and the second “control” group the same broth, but without the probiotic. They found that after 28 days the group fed the probiotic were more confident and willing to enter the maze. 

They were also subjected to a swim test, where more anxious mice will give up and float (due to a stress response called learned helplessness). The probiotic group were less stressed and more willing to swim. The team also found that levels of GABA, a neurotransmitter responsible for sleep and relaxation, was increased. In another Belgian study, designed to discover the optimal microbiome terrain, researchers found that depressed subjects didn’t have two specific breeds of microbes – Coprococcus and Dialister. Two microbes that were present in the participants that had a high quality of life. 


Fixing Gut Anxiety with Pre and Probiotics

Pre and probiotics have been found to promote the proliferation of “good” bacteria in the gut. In turn, reducing anxiety and producing calm. The mechanisms that underly anxiety and gut microbes is separate from inflammation. However, gastrointestinal inflammation seems to reduce the good bacteria’s abilities to communicate effectively with the brain. In one study, mice were infected with the parasite T muris and then given the probiotic – Bifidobacterium longum

Resulting in the probiotic group experiencing less anxiety and normalised BDNF levels. Some of the microbes in your gut also work with your immune system. While others can alter behaviour independently. Several studies have pointed to the vagus nerve as the channel that most microbes use to communicate with the brain. The vagus nerve is a cranial nerve that sends signals to and from the brain to the intestinal tract. The vagus nerve starts at the brain stem and travels down to the gut. 

The Bottom Line

There are over 4000 papers exploring the gut microbiome, and counting, and for good reason. Our gut microbes play an instrumental role in all aspects of health, even our behaviour and mood. Ensuring that you eat a whole foods diet rich in pre and probiotics is a vital component of a healthy lifestyle routine.