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Gut – Brain Axis – the circuit of emotions

Although there is a lot of talk in the press at the moment about depression and anxiety associated with Covid-19, there is not much said about the tight correlation between our central nervous system, the enteric nervous system and our digestive system and how it affects our brain function and behaviour. An extended lock-down and social isolation affects not only those who already suffer with mental health issues but it may lead to a new wave of sufferers who have been subject to unprecedented external factors such as a job losses, grievances or even food poverty.

So what is the Gut Brain Axis and how can it influence the way we behave and how we feel?
The number of microorganisms in our body is 10 times bigger than the number of human cells. Ongoing research confirms that there is a complex interaction between those microorganisms and their moderator, which not only impacts digestion, vitamin secretion (vitB12 and vitK) and energy distribution but also the brain function and our behaviour. Studies show that human microbiota (beneficial bacteria) consists of between 10 – 100 trillion beneficial bacteria and this bacteria is now widely recognised as another organ of the human body! Based on studies conducted on mice, it is suggested that microbiome can play a crucial role in neuropsychiatric illnesses. 

The microbiome-gut-brain relation is a part of our physiological network including the endocrine system which is responsible for the relation between the hypothalamus, the pituitary gland and the adrenal glands our immune system and the enteric nervous system (a mesh – like system of neurons regulating the function of the GI tract).

Magdalena Marvell is a Nutritional Practitioner and Founder of the Persea Clinic which helps support clients who want to optimise their health in areas such as gut health, hormonal balance, skin conditions, weight management, family nutrition. To find out more about her work please visit

The composition of our microbiota depends on our individual genetics, age, lifestyle, diet, stress, infections, antibiotics history and other environmental factors (such as living in an industrial area). Even short term use of antibiotics can temporarily alter microbiome composition and lead to long-term dysbiosis (imbalance in the human microflora). Our central nervous system (represented by our brain), the enteric nervous system (intrinsic nervous system of the gastrointestinal tract) and the digestive system create the gut-brain axis. It has been revealed that there is a symbiotic relation between our microbiota and intestinal cells which takes part in some physiological processes such as digestion, growth and our immune defence. Studies suggest that there may be a correlation between stress-related symptoms such as anxiety and Irritable Bowel Syndrome (IBS) and more than 50% of people suffering from IBS are likely to also suffer from anxiety or depression1.

Through tryptophan (precursor for the serotonin production) metabolism and secretion of a bacterial end – product our microbiome can regulate the HPA axis and the vagus nerve, the longest and most complex cranial nerve which helps to regulate processes in the GI tract. 

The vagus nerve mediates the connection pathways between the intestines and the brain and alteration of microbiota can effect this connection. In a study on rats and mice it has been discovered that bacteria can directly affect the behaviour through the vagus nerve. Contrary to this, dysbiosis caused by pathogenic bacteria in mice affected neural circuits resulting in anxiety-like behaviour. Interestingly the treatment with specific probiotics (Lactobacillus rhamnosus) reduced anxiety and depressive behaviour. Some of our beneficial bacteria (Lactobacillus brevis and Bifidobacterium dentium) can also locally produce and release neurotransmitters such as serotonin and GABA. A study by Takanga et al, suggests that GABA produced by beneficial bacteria can access our Central Nervous System by crossing the blood brain barrier. Its dysfunction can be associated with depression and anxiety.

So if dysregulation of HPA (the relation between hypothalamus, pituitary gland and adrenal glands), a compromised immune system and deficiency of tryptophan metabolism are influenced by the imbalance of our microbiome which in turn can lead to depression, how can we get our beneficial cultures back on track?

Although during the lock down limited food choices can be an issue, finding things in your house or making them from scratch could help your microbiome thrive and alleviate the symptoms of anxiety.

If you find yourself bored during the long weeks of self isolating, you can perhaps experiment with fermentation and try to make some sauerkraut or kefir! These products already contain healthy bacteria and including them in your daily diet can help to repopulate microbiota in your gut. If you struggle with the sour taste then try supplementing with a dietary probiotic instead. Human studies suggest that B.Longum and L.helveticus may improve anxiety and depression2.

Most of the common probiotics contain these strains so ask your health practitioner for advice. 

Prebiotics, non-digestible fibres promote the growth of beneficial bacteria in our gut. These prebiotics can help to increase Bifidobacterium which is beneficial for the gut-brain axis. Good sources of prebiotic include chicory, wild garlic, kale, spinach, carrots and fibrous/woody vegetables such as asparagus, broccoli and bok choy. Beans and cabbage are also a great form of prebiotic! 

Reducing physiological and emotional stress can also help to keep our microflora in a healthy balance. Stress reduces beneficial bacteria and allows pathogenic invaders to overtake. Although it is difficult for some to find headspace during these unprecedented times, a good mediation app (such as Headspace) or cognitive behavioural therapy app (such as Thrive)3 could become your new best friend. Finding 3-5 minutes in the morning for your daily meditation could set up positive thoughts for the whole day.

About 95%4 of our body’s supply of serotonin (neurochemicals regulating mood and cognition) is made in our digestive tract5. Our microbiome produces and responds to the same neurochemicals such as serotonin which may suggest that the brain can regulate our mood and cognition by responding to the feedback it receives from the microbiome5. Incorporating foods containing tryptophan (amino acid, precursor for the serotonin production) for example eggs, turkey, spinach, salmon and pumpkin seeds may help to boost ‘the happy hormone’ (serotonin) levels. Refined sugar and artificial sweeteners (saccharin, acesulfame, aspartame, neotame and sucralose) can alter the type of our microflora and potentially increase the number of pathogenic bacteria (which feed on sugar). 

Swapping refined sugar for snacks sweetened with fruit sugars (such as dates) or stevia and erythritol could be more beneficial in a long term.










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