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Do you have digestive issues (e.g. bloating, food sensitivities), alongside depression, anxiety, autism, or a neurodegenerative condition such as multiple sclerosis (MS)? If so, you need to know about the 'Microbiome Gut Brain (MGB) Axis'.
Over the course of human evolution, trillions of bacteria have taken up residence within our gut, forming our 'gut microbiome' - the phrase on everyone’s lips.1 Research is revealing the far-reaching ways in which these microbes influence our health, not least our mental and neurological well-being.2,3
Our nervous system is the ‘control centre’ of the body, which regulates our mood, response to stressors, movement, and ability to form memories and process information. Our gut microbiome can impact its function, and vice versa, thereby helping us to adapt to our environment, minute by minute. This two-way signalling seems to occur via the vagus nerve which connects the brainstem to the gut. Recognition of this has led to the proposal that the ‘Gut Brain Axis’ should be renamed the MGB Axis.4
Here are some of the most common signs that you need to support it:
1. Depression and anxiety
One study, which looked at more than a thousand people with digestive disorders, found that 84% had anxiety and 27% had depression.5 Another demonstrated that patients with major depressive disorder tend to have gut dysbiosis,6 a further clue about the role of the MGB axis in mental health.
Research in this area is in its early stages. More than 90% of serotonin – our good mood neurotransmitter - is produced in the gut under the influence of the microbiome.7 Meanwhile, Lactobacillus rhamnosus and Lactobacillus plantarum8 can produce gamma-aminobutyric acid (GABA) – our calming neurotransmitter. This gut-derived GABA may be able to calm our core stress axis - the amygdala-hypothalamic-pituitary-adrenal (HPA) axis9 - which can otherwise be hyperactive in anxiety,10 although this has yet to be demonstrated in humans.
Increased intestinal permeability (or ‘Leaky Gut), linked to gluten,11 antibiotics,12 and dysbiosis,13 might also play a role. It can become an insidious source of inflammation, now widely associated with depression.14,15 It enables infiltration of gut-derived substances into circulation, such as lipopolysaccharide (LPS), which trigger inflammation and might also increase activity of the amygdala (the brain region involved in fear perception) and in doing so, mediate depressive16 and anxious behaviour.17
The term ‘psychobiotic’ describes “a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness.”18 Research into the effect of probiotics on depression and anxiety in humans is ongoing and currently hotly debated.19,20,21 For now, it is an empowering prospect which encourages us to think laterally about the drivers of poor mental health and how it can be holistically supported with nutrition and lifestyle.22
2. Behaviour and learning difficulties
Optimising gut health is a clinical priority for those with autism too. Addressing gut dysbiosis, increased intestinal permeability, and constipation are important goals, alongside other interventions, such as support for methylation.23,24
Gut dysbiosis is a common observation amongst children with autism, often involving Clostridium overgrowth.25 Clostridium difficile can produce p-cresol,26 a metabolite often elevated in their urine.27 P-cresol inhibits the enzyme dopamine beta-hydroxylase (DBH), which converts dopamine to noradrenaline. This could give rise to elevated dopamine levels,28 which may underlie some of the behavioural aspects of autism, alongside other factors like poor detoxification29 and high dairy intake.30
Probiotics may consequently offer hope for those with behaviour and learning difficulties. Lactobacillus acidophilus and Lactobacillus rhamnosus, for example, can help to support healthy gut microflora and reduce Clostridium overgrowth. 31,32
3. Neurodegenerative disease
Our gut influences the health of our neurons and neurotransmission. Increased intestinal permeability is regarded as a precondition for the development of inflammatory autoimmune conditions,33 including MS. Equally, gut dysbiosis, including reduced bacterial diversity, has been linked with cognitive decline,34 Alzheimer’s,35 and Parkinson’s.36 Gut health is an essential consideration for those with, or at risk of, neurodegeneration, alongside other measures such as blood sugar balancing37 and detoxification support.38
Are you affected by one of the problems above? If so, supporting your gut with probiotics, prebiotics (e.g. fructooligosaccharide), and nutrients like L-glutamine,39 can be a good starting point, alongside personalised support from a registered Nutritional Therapist.
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2 Dinan T.G et al. Collective unconscious: how gut microbes shape human behaviour. J of Psy Res. 2015; 63: 1-9.
3 Lerner A, Neidhöfer S, Matthias T. The Gut Microbiome Feelings of the Brain: A Perspective for Non-Microbiologists. Microorganisms. 2017; 5 (4): 66.
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24 Frye RE et al. Effectiveness of methylcobalamin and folinic acid treatment on adaptive behaviour in children with autistic disorder is related to glutathione redox status. Autism Research and Treatment. 2013.
25 Parracho HM et al. Differences between the gut microflora of children with autistic spectrum disorders and that of healthy children. J Med Microbiol. 2005;54(Pt 10):987–99
26 Selmer T, Andrei PI. p-Hydroxyphenylacetate decarboxylase from Clostridium difficile. A novel glycyl radical enzyme catalysing the formation of p-cresol. Eur J Biochem. 2001; 268 (5): 1363-1372.
27 Persico AM, Napolioni V. Urinary p-cresol in autism spectrum disorder. Neurotoxicology and Teratology. 2012; 36: 82–90.
28 Goodhart et al. Mechanism-based inactivation of dopamine beta-hydroxylase by p-cresol and related alkylphenols. Biochemistry. 1983; 22(13):3091-6.
29 Esparham AE et al. Nutritional and metabolic biomarkers in Autism Spectrum Disorders: an exploratory study. Integr Med (Encinitas). 2015; 14 (2): 40-53
30 Sokolov O et al. Autistic children display elevated urine levels of bovine casomorphin-7 immunoreactivity. Peptides. 2014; 56: 68-71.
31 Armuzzi A et al. Effect of Lactobacillus GG supplementation on antibiotic-associated gastrointestinal side effects during Helicobacter pylori eradication therapy: a pilot study. Digestion 2001; 63 (1):1-7.
32 Johnson et al. Is primary prevention of Clostridium difficile infection possible with specific probiotics? Int J Infect Dis. 2012 Nov;16(11):e786-92.
33 Fasano A. Leaky gut and autoimmune diseases. Clin Rev Allergy Immunol. 2012; 42 (1): 71-8.
34 Desbonnet L et al. Gut microbiota depletion from early adolescence in mice: Implications for brain and behaviour. Brain Behav Immun. 2015 Aug;48:165-73.
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37 Kroner Z. The relationship between Alzheimer’s disease and diabetes: Type 3 diabetes? Altern Med Rev. 2009; 14 (4): 373-9.
38 Martyn et al. Geographical relation between Alzheimer’s disease and aluminium in drinking water. Lancet. 1989 Jan;333(8629):61-62.
39 Farhadi et al. Intestinal permeability and systemic infections in critically ill patients: effect of glutamine. Crit Care Med. 2005; 33 (5): 1125-35.