Did you know that the human gut holds over 100 trillion bacteria! There are in fact more bacteria in the human body than there are human cells, which are approximately 60 trillion in number. These 100 trillion bacteria, are responsible for 70% of the body’s immune system, so any imbalance or deficiencies here are bound to have some impact on one’s overall health.


Bacteria are typically made up of just a single cell. Unlike the cells that make up the human body they do not have a membrane-bound nucleus. Neither do they have membrane-bound organelles, such as the mitochondria, which are effectively the batteries found in all cells.


Although bacteria are often perceived as the enemy, the fact is that the vast majority of the bacteria found in the gut are bound up with our immune systems and are also essential to healthy digestive functioning. Gut microorganisms benefit the host by collecting the energy from the fermentation of undigested carbohydrates and the subsequent absorption of short-chain fatty acids. This incredible relationship begins from the moment we are born, because most of the microflora found in the gut, which includes bacteria, comes from the mother’s birth canal and is transferred to the child during the birth process.


By the time we are fully developed as adults the bacteria that lives in the gut weighs about the same as the human brain. There’s an interesting parallel here because the latest research looking at the connection between the gut and the brain, is helping us to understand that there is a busy dual carriageway between the two. This is why the gut has come to be known as the ‘second brain’ – whatever is happening in the one organ is mirrored pretty accurately in the other. Such is the connection between the two that it is now being postulated that the microbiota found in the gut could be involved in a host of conditions such as: anxiety, obesity Parkinson’s disease and a range of mood-related conditions. For those who wish to explore this further, you might also be interested in the Polyvagal Theory and neuroception – see the work of Stephen Porges.



What does the research indicate

This relationship between gut flora and various physiological conditions is a complex one and the research continues to mount. Dr Jane Foster (McMaster University in Canada) has done a lot of groundbreaking work, which is highlighting the relationship between microbiota and behaviour. However, the results are not yet conclusive – what is clear, is that the flora in the gut does influence mood and anxiety and this is particularly noticeable when the levels of good bacteria are insufficient.


The growing evidence that what is happening to the bacteria in our guts is in fact influencing our mood and with that our behaviour, is something that we now need to take very seriously indeed.  Our obsession with and overuse of antibiotics, in order to rid the gut and the body of bad bacteria, has led to a situation where ‘healthy bacteria’ is eliminated in the process. What we are discovering now is that this doesn’t simply lay us open to re-infection from a variety of pathogens but it also leads to dysfunction in the brain and the mind.


The work of Professor Emeran Mayer (a gastroenterologist at the University of California, Los Angeles) has exposed the connection between the age of our bodies and the activity, or reduced activity of the microbiota. His work has exposed that the lack of maturation in children of the healthy flora in the gut is one of the reasons they remain vulnerable to their environments, especially in their first three years.  Interestingly the picture is similar as we get older.


In other words, as we get older, the bacterial quota in the gut starts to decline both in terms of diversity and abundance, and then what is observed could be described as a reverting back to a childhood state of immunity/vulnerability. Professor Mayer, has concluded that it is very likely that the deterioration of brain functions we see in the elderly is strongly connected to the reduction of healthy bacteria in the gut, which could at least in part explain the rise in the incidence of dementia, Alzheimer’s etc.


The mechanisms and processes at work here have not yet been fully understood but what we know is that the gut bacteria and/or the molecules they produce, interact with the vagus nerve in the gut (the vagus nerve is considered to be the primary dual carriageway between the brain and the gut). This interaction in turn affects hormonal signalling and the immune system via the neurons within the gut lining and the vagus nerve. This sophisticated communication between the gut and the brain is influenced moment by moment by what is happening in terms of the good and bad bacteria – according to their respective levels our physical and mental health is either reduced or enhanced.


Professor John Cryan (from the University of Cork) found that the impact of the probiotic Lactobacillus rhamnosus on mice,  dampened down their anxiety, they actually ‘chilled out’, and their brain chemistry was altered. Professor Cryan, also noticed that when the vagus nerve was cut this reduction in anxiety was no longer observed. However because some studies have not duplicated this outcome, there are almost certainly other factors at play.   But the role of the vagus nerve and the complex network that communicates with the brain is certainly part of this equation.



Psychobiotics and mental health

In one trial healthy people given a blend of the probiotics, Bifidobacteria and Lactobacillus for 30 days were found to fare better according to their answers in questionnaires which sought to assess anxiety, depression and stress levels, than those who were given a placebo. This has led to the development of ‘psychobiotics’ – which is the system where probiotics and prebiotics are prescribed to help treat people who are suffering with various mental health conditions.


The medicine of tomorrow almost certainly will include taking the microflora of the gut more seriously and prescribing probiotics and prebiotics alongside other treatment regimes. There is, however, a word of caution coming out of this research, namely that much of the research has been done on mice and may not always translate to humans in the same way.  Also, given the huge numbers and types of bacteria it is difficult to know exactly which particular strains are impacting on our mental health in a detrimental way.


Prebiotics are substances we cannot just digest but are believed to promote good bacteria in the gut. Prebiotics occur naturally in some foods and include carbohydrates such as inulin, galacto-oligosaccharides and FOS.  Probiotics on the other hand are live microbes. They are often administered in liquid drinks, supplements and yoghurt. The health benefits of probiotics are quite wide and varied, as each strain has different capabilities and potential.



Physical and mental health are entwined

Research involving Dr Kersten Tillisch and Professor Emeran Mayer found that probiotics within as short a period as four weeks actually influenced the connectivity between various brain regions.


In this research, a group of women split into three categories, those having a probiotic yoghurt, those having a probiotic-free dairy product and the third group having nothing at all, were compared over this four week period.


Their brains were scanned at the beginning using functional magnetic resonance imaging (fMRI) and after four weeks the brains were scanned again.  There was a clear difference between the way their brains connected in the resting state.  What was of particular note is when the women were shown images of angry or frightened faces the probiotic group showed a marked decrease in the activity of the brain regions involved with emotion and sensation. Dr Tillisch and Professor Mayer concluded that the gut-brain relationship is clearly an intimate one, where the bacterial ecosystem has a bearing on the brain and human emotions.


So we believe a new paradigm is needed, one where we appreciate that physical and mental health are entwined and so our health strategies increasingly need to move in this direction.



The way forward?

We would not recommend on the basis of the ever-growing research that an individual mindlessly takes pre or probiotics, without looking at their health in a holistic way.


This means examining diet, hydration, sleep, exercise, nutrition in the widest sense as well as one’s thoughts (self talk). Without proper attention to all these areas, looking exclusively at the connection between the gut and the brain is likely to be insufficient when dealing with the complexities of mood, personality and behaviour.


Assuming that you are addressing all the other relevant aspects of health, choosing a probiotic to supplement your diet is generally an excellent option. When doing so it is much better to choose a probiotic which has in excess of 20 billion viable organisms and also has a multi-strain profile. This ensures much better protection and is more likely to help you achieve the results you’re looking for.



Here as some of the main strains to look out for:

Lactobacillus acidophilus – this bacterium is like the multivitamin of probiotics, as it benefits your entire digestive tract. It also helps fortify the immune system and prevents the development of unhealthy yeasts and bacteria like Candida albicans, Salmonella, E. coli and Staphylococcus aureus to name a few.

Bifidobacterium bifidum – this strain is particularly beneficial after taking a course of antibiotics, which can lower the immune system because of the destruction of healthy flora in the gut.  This can cause yeast infections or thrush. It is generally beneficial against intestinal infections, diarrhoea and cirrhosis of the liver.

Bifidobacterium lactis – helps to soothe a swollen or inflamed colon, as it contains microorganisms that live within the colon helping with the elimination of toxic waste. This makes it an excellent probiotic dealing with those who are plagued by diarrhoea and so it is extremely helpful to take when one is travelling where there is a change in water sources and other environmental factors.

Lactobacillus plantarum – this amazing probiotic manages and monitors nutrients to ensure they reach the cells. Vitamins such as B1, B2, B3, B5, B6, B12 and vitamins A and K are all better absorbed when the gut is rich in Lactobacillus plantarum. Recent studies also indicate that this strain can help regulate blood pressure levels.

Bifidobacterium breve – is absolutely essential for the complete and thorough breakdown of all foods. It helps in the fermenting of sugars, which produce lactic acid and acetic acid, which are essential for healthy digestion. When there are sufficient quantities of Bifidobacterium breve, there is a reduction in flatulence, diarrhoea and other bowel irritations, such as IBS.  Amongst its many virtues, is its ability to inhibit the growth of E. coli.




As this article has hopefully demonstrated, bacteria are not to be feared but rather they need to be understood. We actually couldn’t survive without healthy bacteria and many functions in our bodies would be compromised or simply fail.


It’s clear we need to develop a proper respect for bacteria, not just because they are vital for our physical health but as demonstrated here, they are critical for our mental health too.


This is why we at Reach are so keen for a truly holistic strategy, one which recognizes that the mind cannot be properly ‘fixed’ if we ignore the needs of the body, and the body cannot reach its optimum potential if the mind is not properly catered to. They are intimately entwined. This is why we have created a model that respects this intimate relationship and actively promotes a marriage between psychology and biology.


If you’re not sure how to proceed always seek out professional advice from your GP or a qualified nutritionist/health professional.


Also see: Anxiety – addressing causes not just symptoms and The Science of Autistic Spectrum Disorder