The gut
is not just the site of your digestion it is also a key
part of your immune system and the site of a good deal of the information
relayed to and from your brain. It has even been called the ‘second brain’ or ‘enteric brain’ as it contains 100
million neurons i.e. more neurons than the spinal cord or peripheral nervous
system combined[i].
It is responsible in no small part for how you feel; your mental state, mood
and health. For instance, 95% of the feel-good chemical serotonin in your body
is found in your gut. This fact has been suggested as the reason why many
mental diseases have correlates in the gut e.g. autism and depression often
have gut symptoms associated with them.
Vitally,
via the roughly 100 trillion bacteria that it contains,
called the gut microbiome, it
contains enough bacterial DNA to produce a vast array of the metabolic products
(vitamins, neurotransmitters, enzymes, and signaling proteins called
neuropeptides) that our body needs to function. It has been said the human
being is simply a highly evolved, complex host for bacteria In fact,
evolution has shown us that bacteria have often been instrumental to the
development of the organism, as they have developed in symbiosis with us[ii].
Babies born via Caesarian section often have poor gut function as they have not
been properly inoculated with their mother’s gut flora via a vaginal birth[iii].
This may cause the children to have more allergies and health issues than
children born normally, including mental health problems. Given the increasing
use of C-section in hospitals, and the likelihood of deficiencies being passed
on from that child when she too has
baby, this has health implications for us as a society not just as individuals.
The
importance of the gut in general health is often ignored. Nutrition is mostly
ignored when you engage with conventional medicine. How often has your doctor
asked you about your diet when discussing your mental – or even your physical - health?
Having a good balance of gut flora is vital – I am not looking at purely
psychological factors here as I am only too aware that the balance of your gut
microbes is crucial to your mental functioning. Your gut microbiome balance is
vital to functioning. Unfortunately as your microbes get more out of balance,
your digestion becomes poorer, you intake less vital nutrients and your gut
gets further depleted and imbalanced. Opportunistic bacteria and resident
yeasts begin to take hold. Symptoms are gas, bloating, itchy, flaky skin,
cravings for sweet foods, and ‘foggy’ brain. You can see it is a cycle: poorer
digestion – less nutrients and higher yeasts – poorer digestion.
Figure
1 Digestive tract and immunity
Let’s
look at one example of how this works. The gut is one of the most important
sites of your immune system – the gut
wall is, after all, a form of modified skin and as such is an entry point of
pathological microbes (i.e. the unfriendly type!). Hence it’s not surprising
that the most evolutionarily ancient immune function (called the ‘innate immune
system’), is based here. It is the essential non-specific first-line defence to
invasion controlled by the release of inflammatory molecules called cytokines. These are peptides (small proteins) produced in the
body which control
inflammation. Continuous stimulation by bacterial structural cell wall sugars
called lipo-polysaccharides activate the immune system to be in a state of
constant alert, helping to keep it activated. Bacteria keep us primed!
The
release of cytokines is controlled by the balance of these polysaccharides and
it helps the body maintain its immunity and, via their or its interaction with
the stress response, even its normal sleep pattern (they are involved with the
transition to Rapid Eye Movement sleep from non-REM sleep). This
is important for dreaming and restful sleep. So, the balance of your gut flora
influences your immunity and the quality of your sleep; therefore both directly
and indirectly affecting your health using bi-products of their metabolism.
This leads to the perhaps surprising conclusion that bacteria are essential to
our physical wellbeing.
However,
they also govern the balance in your mood and anxiety levels via the serotonin
and other neurotransmitter levels they produce. Surprisingly most of the
serotonin in your body is found in your gut. This is why when we increase
levels via anti-depressants (the SSRIs like Prozac reduce re-uptake) you often
get gut problems as a side-effect; oo much serotonin is just as much of a
problem. So gut flora are vital for mental health too.
Another
factor influenced by your gut bacteria is the permeability of your gut. With a
standard western diet (also called the ‘standard American diet’ (SAD) in the US), your ‘bad’ bacteria are
encouraged to overgrow which can cause the cells in your gut to become ‘leaky’
i.e. the gaps between the cells instead of having ‘tight junctions’ as normal,
develop gaps. If you were unlucky enough to have
childhood infections and were then prescribed extensive antibiotics these can
affect gut flora for life too and exacerbate the problem. Antibiotics are non-selective
about which bacteria they kill – the same is true of ‘anti-bacterial’ handwashes
which are highly damaging to the gut.
Toxic bacterial
overgrowth can encourage auto-immunity as undigested protein fragments
(peptides) and toxins are able to penetrate through the gut wall causing the
body to react with an immune response to food as if it were an invader. The
cells in the gut are meant to be a semi-permeable barrier, finely controlled so
as to only allow certain things in. When this control fails by the cells being
permanently open, the barrier is broken and disease may result. Excessive
permeability has been implicated in such definitive auto-immune conditions as
diverse as coeliac disease, multiple sclerosis and chronic fatigue syndromes.
So,
leaky gut syndrome is a precursor to many diseases as the gut is key in
regulating so many bodily functions. In addition to the direct effects on
immunity and inflammation, there are more factors in gut functioning that
impinge on your health. The short-chain fatty acids (breakdown products of
indigestible carbohydrate in your diet produced by your gut bacteria) are epigenetic regulators;
that is they help to control what genes are expressed in the cells. These epigenetic
effects of the gut flora help to explain why each of us reacts differently to
our environment – since each of us has an individual gut flora we have a unique
response to the external environment. Those with a healthy gut not only have a
healthier immune system but digestion and metabolism work better, with more
nutrient availability, more accurate genetic regulation and intercellular
communication. It can’t be overstated how important this is for brain function,
especially in the area of pain response.
Although
we are all familiar with the idea of ‘gut feelings as a source of information,
we are seldom aware how vital the gut is in central nervous system (CNS)
function. The enteric (gut) brain really does exist and it is just as important
as the brain in your head. Stress (whether conscious and acute, or unconscious
and chronic) alters the balance of your gut flora via the release of hormones
like adrenaline and cortisol (from the adrenals) and cytokines produced by
bacteria. The self-regulating system is sent haywire and the results are systemic (i.e. throughout your body). These findings are so important, the
study of these interactions now has its own field
This is an extract from my book Stress, Trauma and Unresolved Emotion in Chronic Disease.
See
here to purchase copies (digital or paperback)
[i]Hadhazy,
Adam.(2010). Think Twice: How the Gut's "Second Brain" Influences
Mood and Well-Being. Scientific American.
February 12
[ii]
Yatsunenko, et al. (2012). Human gut microbiome viewed across age and
geography. Nature, 48 6(7402), 222–227. doi:10.1038/nature11053
