The term 'stress' is broadly defined as a reaction to a stimulus or threat that is either real or perceived. Stress is useful in small doses. It stimulates reactions to avoid danger, motivates us to work towards a goal or strive for success. However, when stress becomes chronic and persistent, our physical and mental well-being suffers.
Hippocrates, regarded as the founder of medicine, was once quoted for saying ‘all disease begins in the gut.’ Our gut does more than send us on a trip to the bathroom everyday. The gut is largely responsible for the critical functions of the body’s digestive and immune system, and has been directly linked to our behaviour, mood and mental health.
The health of our gut is compromised when the body is under chronic stress, wreaking havoc on its ability to function properly. If you suffer from a gut related issues (e.g. irritable bowel syndrome), you’ve probably tried every ‘diet’ under the sun (gluten free, dairy free, the low fodmap diet). But, it may surprise you to learn that chronic stress could be the real cause of your irritated gut.
Our 'Second Brain'
We have all experienced the phenomenon of the ‘gut feeling’. We get ‘butterflies’ in our stomach when we are nervous, we see something ‘gut-wrenching’ or we ‘go with our gut’ when faced with a difficult decision. It turns out that the ‘gut feeling’ is a real physical phenomenon, not folklore. To understand why our tummy serves as a repository for feelings we commonly associate with the brain, we need to understand how the gut and the brain are intrinsically linked.
The gut possesses an unimaginable amount of nerves, so much so that it’s been coined the ‘gut brain’. These nerves help us to ‘feel’ our inner world (together they are referred to as the Enteric Nervous System or 'ENS') and through a series of complex neural pathways relay the information they receive back up to the brain (the Central Nervous System or 'CNS'). The channel of communication between the CNS and ENS is referred to as the ‘Brain-Gut Axis’. Interestingly, the dialogue between these two systems goes both ways - our gut sends signals to the brain and the brain sends signals to the gut. This explains why you stop eating when you are full (the stomach becomes distended and communicates this to the brain), and why your stomach is the repository for all sorts of feelings when you are nervous or overcome with emotion.
The Fight or Flight Response
Stress is thought to be among the most important stimuli discussed by the brain and the gut. When we come into contact with a stressor, the hypothalamic-pituitary-adrenal (HPA) axis (imagine this as our internal ‘stress control’ center) instigates the production of a chemical called corticotropin-releasing factor (CRF). CRF triggers a cascade of other chemicals which eventually cause the release of cortisol (commonly known as the stress hormone). Cortisol diverts energy away from the gut to our muscles and brains, works to keep blood sugar elevated (to meet glucose demands of the brain) and retention of sodium (to keep blood sugar up), all of which allow us to respond quickly and efficiently to danger.
The fight or flight mechanism works best as a temporary response to help with survival. Our ancestors suffered from ‘acute stress’ if they found themselves, for example, fleeing from a sabretooth tiger #cavemanproblems. However, our bodies were not designed to handle long term, chronic stress. In this day and age, our lives are no longer filled with occasional stressors that come and go for short, interspersed periods of time. Rather, with looming deadlines at work, financial burdens, social pressure and the constant inundation of information, it’s safe to say that for the majority of the Western World we are stressed for the most part of a day, most days. In other words, we are in ‘fight or flight’ mode more often than not. As energy is diverted away from the gut during the fight-or-flight response, digestion and immune function are slowed or halted for long periods of time, which can rob us of key nutrients and expose the gut to infection and inflammation.
The remainder of this article seeks to provide a broad overview of the physiological changes that occur in our body when we are suffering from chronic stress (or perpetual fight or flight mode), and the impact of chronic stress on the composition of gut bacteria.
INCREASED GUT PERMEABILITY
Just as your skin forms a barrier between your inner body and nasties from the outside world, your gut prevents any nasties entering your body beyond the gut wall. It is the gatekeeper, the nightclub bouncer, the Gandalf of your internal self (You shall not pass!).
When we are exposed to chronic stress the lining of the intestine becomes damaged and porous (visualize an umbrella with holes in it). This loss of integrity of the gut lining allows large, undigested food molecules, toxins and waste (you could collectively think of these as drunk gatecrashers) to flow freely into your bloodstream through the porous-like holes in the gut’s lining. The process of increased permeability is often referred to as ‘leaky gut’.
Some research suggests that mast cells are to blame for gut permeability in times of stress. Mast cells, found in the gut’s mucosal wall, contain receptors and are responsive to the amount of CRF flowing through the body (remember, CRF is released by the brain during times of stress). Researchers studying rats under water aversion stress found that rats with no mast cells in their intestines didn’t show increased intestinal permeability under stress, whereas rats with mast cells did. What this tells us is that unstable and degranulated mast cells may lead to intestinal permeability.
Increased permeability causes an exaggerated immune response, chronic inflammation, and messes with the composition of bacteria residing in the gut.
The tissues in and surrounding the gut house about 70% of our body's ENTIRE immune system. This sounds impressive, but it makes perfect sense - on any given day, our gut is exposed to not only the food we eat but foreign pathogens like bacteria, food proteins, parasites, fungi, toxins and viruses which we inadvertently consume. Should any of these nasties make their way through the gut barrier, our gut-associated immune system is triggered and attacks any foreign substance it does not recognize. An inundated immune system causes an exaggerated and prolonged immune response, and this can lead to a myriad of problems such as the development of food sensitivities, systemic inflammatory disorders, irritable bowel syndrome, and autoimmune disease.
One theory is that our immune system falters under chronic stress because stress suppresses the production of an antibody called secretory IgA (sIgA). The role of sIgA antibodies, simply put, is to attach themselves to invading nasties, trap them in mucus and stop them from going somewhere they shouldn't. These clever little antibodies then neutralize any damaging toxins given off and help ensure the invaders are shown the door via feces. As we produce less and less sIgA our gut becomes a playground for inflammation and harmful bacteria.
Inflammation is, generally speaking, the body’s immune response to a stimulus. When foreign substances permeate the gut lining the gut’s immune system is triggered and an inflammatory response is turned on.
Cortisol (remember, this is the stress hormone), plays a significant role in turning off inflammatory reactions. For example, if you cut your finger, cor