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How Stress Affects Gut Function & Thence General Health & Well-being

This week I've been following the "Microbiome 2 Summit" (the microbiome being the population of micro-organisms living in the gut which are so key to health) and there have been a couple of talks linking stress and gut health, and thus explaining why, as is often quoted, 75% plus of GP visits are for stress related ailments. I thought I would write an article explaining the science behind the link - which is pretty well established.

Stress Response - Fight or Flight

The stress response, also known as fight-or-flight response, is your body's reaction to challenge, that mobilises and prioritises energy to help you deal with the stressor. (As long as it's short term, the stress response is a very useful thing to have happen). The stress response is communicated to the body via (i) the autonomic nervous system (the sympathetic branch activates, the parasympathetic branch relaxes) and via hormones (especially the "HPA axis" which triggers release of the hormone cortisol).

In broad terms, the sress response diverts energy away from the gut and digestive functioning, because that's a lower priority (at least in the immediate to short term).

Digestive Secretions Decreased

Stress lowers secretion of both stomach acid and digestive enzymes. The result is that food is not digested as well. This can lead to malabsorption of nutrients (which can be a problem in itself if you are nutriten deficient), but also to damage of the gut itself via two connected mechanisms.

Two Mechanisms Behind Gut Health Problems

These two related mechanisms are (i) increased gut permeability (or leaky gut) and (ii) dysbiosis or a shift in the micro-organism population towards "unhealthy".


Dysbiosis means a relative predominance of "unhealthy" bacteria etc. over healthy. The balance in the microbiome is key to inflammation (which I'll say more about later). Dysbiosis also can trigger increased permeability.

Gut Permeability

The lining of the small intestine is only 1 cell thick - and it can be easily compromised. When it is, more material gets through and into the blood supply, that shouldn't (i.e. you have raised permeability). It could be simply partially digested food, or by-products from gut micro-organisms (e.g. LPS). Both of these trigger the immune system. If you have persistently raised permeability (leaky gut syndrome) the result tends to be chronic inflammation.


Inflammation is a response of the immune system designed to help you repair damage at a cellular level, and also repel any infections or toxic intrusions. Like with stress, it's a good thing to have as a short term option but chronic inflammation is damaging - in fact it's linked to just about any chronic illness you can think of, including diabetes, cardiovascular disease, cander and depression.

In depression, it seems that inflammation communicates itself to the brain - the brain has its own immune system in the form of cells called microglia - and it seems this is hard to turn off. 

Functional Medicine - Addressing Underlying Causes

You may have heard of a new paradigm of medicine that is emerging, particularly in the US, less well-known in the UK. The FM approach is to address the underlying factors that cause or maintain health problems. Leaky gut and dysbiosis are very often part of the mechanism of illness, and can be countered on their own level, but you also need to learn to manage stress.

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