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In recent years, multiple studies have provided convincing evidence that the microbes lining your gut interact with your brain through a bi-directional communication pathway – the so-called “gut-brain-axis1.  Through this pathway, gut microbes exchange chemicals with our brain, some of which can significantly influence different neurological conditions. 

Gut Microbes & Your Brain - The Basics:

Neurological conditions like depression, Parkinson’s disease, anxiety or autism (among many others) have been linked to the gut microbiome. Just how much influence these tiny inhabitants exert on our brain is still a topic of active research. But, the idea that gut microbes influence our mental health is not new. About 100 years ago, medical researchers were already talking about gut microbes and mental health, as described by this statement published in a leading medical journal from 1914:

“The control of man’s diet is readily accomplished, but mastery over his intestinal bacterial flora is not…the innumerable examples of autointoxication that one sees in his daily walks in life is proof thereof. They are the cases that present…malaise, total lack of ambition so that every effort in life is a burden, mental depression often bordering upon melancholia…”

Today, we know more about how gut microbes influence brain function and what factors are at play.

The gut - brain connection

A bi-directional communication pathway exists between the billions of microbial inhabitants of our gut and our brain. Biochemical molecules are exchanged between these two systems, affecting almost every function in our body.

gut to brain axis diagram

Signals travel through the enteric nervous system, which comprises a network of neurons spread throughout layers of gut tissue.

Microbes within the gut produce chemicals that reach the brain and influence multiple functions.

Gut microbes produce many biochemical molecules, such as hormones and neurotransmitters, interacting with the enteric and central nervous systems. Through this interaction, gut microbes can influence anything from metabolic functions to neurological diseases.

How strong is the evidence surrounding gut microbes and our brain?

So far, most studies in this area have shown some fascinating correlations between gut microbiota and mental health. Most studies to date have been based on animal models, such as mice and rats. Some of these studies have shown that the brain of animals raised without gut microbes fails to develop normally1. Other studies have shown evidence linking depression and anxiety in mice2. For example, Lactobacillusspp., a common gut inhabitant, produces serotonin and gamma-aminobutyric acid (GABA). Low serotonin levels have been linked to depression, whereas GABA is a key inhibitory neurotransmitter with anti-anxiety and relaxant effects.

 

In humans, studies have identified clear connections between gut microbes and the brain. For example, a 2013 study was the first to address the intriguing question of how gut microbes affect their hosts’ brains in humans4. Here, 36 healthy women from Los Angeles, California, were randomly assigned one of three treatments. The intervention group drank a fermented milk concoction hosting several gut microbes, primarily members of the Bifidobacteriales order, such as Lactococcus lactissubsp lactis and Lactobacillus bulgaricus. The two other groups worked as controls, receiving non-fermented milk products or no treatment at all. Participants then tracked their brain function by functional magnetic resonance imaging (fMRI) before and after ingestion of the microbial cocktail. The fMRI measured participants’ responses to emotional faces and measured their resting brain activity. Their results were clear cut: drinking probiotics changed how the brain responded to the emotion recognition task. The brains of participants who drank the probiotic drink showed reduced connectivity, suggesting an alteration in the processing of sensory information.

 

Other studies have provided strong evidence linking gut microbes to depression5, Parkinson’s disease6, schizophrenia7, brain development8, autism9and age-related cognitive decline10.

Implications for your health

Brain health is intimately linked with your gut microbiome, so a critical question you need to answer is whether you are taking all necessary measures to have a healthy gut.

 

Your gut microbiome is easily altered by external factors, such as diet11, exposure to antibiotics12, and even unhealthy sleeping habits13.

Among these factors, diet is one of the most important and one you can easily control. In a recent review published in the journal Nature, researchers addressed the interaction between diet and gut microbes and how they impact heath14. Some of their key observations include:

 

  • Following a diet rich in sugar and certain fats or consuming processed foods containing certain
    emulsifiers can lead to gut decreased gut dysbiosis when there is an imbalance in your gut
    microbiome15.
  • Fibre consumption is vital for gut health. Fermentation of fibre in the gut results in the production of short-chain fatty acids (SCFAs), which can affect brain chemistry and play essential roles in maintaining intestinal immune equilibrium and protecting against inflammation and cancer16.
  • Fat consumption has a direct effect on the makeup of your gut microbiota. A diet rich in saturated and trans fats, for example, can lead to an excessive number of certain bacteria that can contribute to the development of disease17.

Several other factors have been identified that affect your gut microbiome and your health. These include consuming processed meats, food additives (like ketchup!), certain minerals, and plant-derived bioactive nutrients13.

Our approach to optimal mental health includes an evaluation of your gut microbiome and how your lifestyle might be affecting it.

 

As a result, we have successfully treated patients at our Perth centre with cognitive problems and mood disorders such as anxiety, depression and anger. We have also seen significant progress in treating children with Attention deficit hyperactivity disorder (ADHD) and Autism.

References

  1. Control of brain development, function, and behavior by the microbiome. 2015; Cell host & microbe, 17(5), pp.565-576. Read it!
  2. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences. 2011; 108(38), pp.16050-16055. Read it!
  3. Gut microbiome remodeling induces depressive-like behaviors through a pathway mediated by the host’s metabolism. 2016; Molecular psychiatry, 21(6), p.786. Read it!
  4. Consumption of fermented milk product with probiotic modulates brain activity. 2013; Gastroenterology, 144(7), pp.1394-1401. Read it!
  5. The neuroactive potential of the human gut microbiota in quality of life and depression. 2019; Nature microbiology, p.1. Read it!
  6. Gut microbiota are related to Parkinson’s disease and clinical phenotype. 2015; Movement Disorders, 30(3), pp.350-358. Read it!
  7. Genomics of schizophrenia: time to consider the gut microbiome? 2014; Molecular psychiatry, 19(12), p.1252. Read it!
  8. Normal gut microbiota modulates brain development and behavior. 2011; Proceedings of the National Academy of Sciences, 108(7), pp.3047-3052. Read it!
  9. Human Gut Microbiota from Autism Spectrum Disorder Promote Behavioral Symptoms in Mice. Cell, 177(6), pp.1600-1618. 2019; Read it!
  10. Cognitive decline, dietary factors and gut–brain interactions. 2014; Mechanisms of ageing and development, 136, pp.59-69. 
    Read it!
  11. Pregnancy-related changes in the maternal gut microbiota are dependent upon the mother’s peri conceptional diet. 2015; Gut microbes, 6(5), pp.310-320. Read it!
  12. Early life antibiotic‐driven changes in microbiota enhance susceptibility to allergic asthma. 2011; EMBO reports, 13(5), pp.440-447. Read it!
  13. Trans kingdom control of microbiota diurnal oscillations promotes metabolic homeostasis. 2014; Cell, 159(3), pp.514-529. Read it!
  14. You are what you eat: diet, health and the gut microbiota. Nature Reviews Gastroenterology & Hepatology, p.1. Read it!
  15. Understanding the Role of the Gut Microbiome and Microbial Metabolites in Obesity and Obesity-Associated Metabolic Disorders: Current Evidence and Perspectives. 2019; Current obesity reports, pp.1-16. Read it!
  16. Activation of Gpr109a, receptor for niacin and the commensal metabolite butyrate, suppresses colonic inflammation and carcinogenesis. Immunity, 40(1), pp.128-139. 2015; Read it!
  17. Metabolic endotoxemia initiates obesity and insulin resistance. Diabetes, 56(7), pp.1761-1772. 2007; Read it!

 

  1. Control of brain development, function, and behavior by the microbiome. 2015; Cell host & microbe, 17(5), pp.565-576. Read it!
  2. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences. 2011; 108(38), pp.16050-16055. Read it!
  3. Gut microbiome remodeling induces depressive-like behaviors through a pathway mediated by the host’s metabolism. 2016; Molecular psychiatry, 21(6), p.786. Read it!
  4. Consumption of fermented milk product with probiotic modulates brain activity. 2013; Gastroenterology, 144(7), pp.1394-1401. Read it!
  5. The neuroactive potential of the human gut microbiota in quality of life and depression. 2019; Nature microbiology, p.1. Read it!
  6. Gut microbiota are related to Parkinson’s disease and clinical phenotype. 2015; Movement Disorders, 30(3), pp.350-358. Read it!
  7. Genomics of schizophrenia: time to consider the gut microbiome? 2014; Molecular psychiatry, 19(12), p.1252. Read it!
  8. Normal gut microbiota modulates brain development and behavior. 2011; Proceedings of the National Academy of Sciences, 108(7), pp.3047-3052. Read it!
  9. Human Gut Microbiota from Autism Spectrum Disorder Promote Behavioral Symptoms in Mice. Cell, 177(6), pp.1600-1618. 2019; Read it!
  10. Cognitive decline, dietary factors and gut–brain interactions. 2014; Mechanisms of ageing and development, 136, pp.59-69. 
    Read it!
  11. Pregnancy-related changes in the maternal gut microbiota are dependent upon the mother’s peri conceptional diet. 2015; Gut microbes, 6(5), pp.310-320. Read it!
  12. Early life antibiotic‐driven changes in microbiota enhance susceptibility to allergic asthma. 2011; EMBO reports, 13(5), pp.440-447. Read it!
  13. Trans kingdom control of microbiota diurnal oscillations promotes metabolic homeostasis. 2014; Cell, 159(3), pp.514-529. Read it!
  14. You are what you eat: diet, health and the gut microbiota. Nature Reviews Gastroenterology & Hepatology, p.1. Read it!
  15. Understanding the Role of the Gut Microbiome and Microbial Metabolites in Obesity and Obesity-Associated Metabolic Disorders: Current Evidence and Perspectives. 2019; Current obesity reports, pp.1-16. Read it!
  16. Activation of Gpr109a, receptor for niacin and the commensal metabolite butyrate, suppresses colonic inflammation and carcinogenesis. Immunity, 40(1), pp.128-139. 2015; Read it!
  17. Metabolic endotoxemia initiates obesity and insulin resistance. Diabetes, 56(7), pp.1761-1772. 2007; Read it!