Strap yourselves in with a cup of herbal tea because this is a wordy one!

The intricate link between the digestive tract and mood is coming to light both in the scientific literature and popular health culture, with the topic of gut health on (almost) everyone’s minds! This post may especially be of interest to you if you experience frequent anxiety, stomach upset related to stress, depression, IBS or all of the above.

There is a bi-directional axis between the gut and the brain, with the gut sometimes referred to as the second brain! Indeed there are over 2 million nerve cells lining the gut, constantly working in communication with the digestive organs and the brain. We don’t have to look very far to find situations where the gut is affected by the brain and vice versa.

When I refer to the ‘brain’, I am also referring to the central nervous system which constitutes the brain, spinal cord and cranial nerves. By ‘gut’ I am talking about the whole digestive tract, from the mouth and tongue, to the oesophagus (food tube), stomach, intestines and anus.

Whilst the gut and brain are connected by the nerves (notably the Vagus nerve), they’re also connected by hormones and the immune system.

How does the brain influence the gut?

An obvious example is when we smell onions frying and all of a sudden, we start salivating and our appetite sky-rockets. The delicious smell is communicated to the brain by the olfactory nerve. The information triggers our salivary glands to secrete saliva and even the parietal cells in our stomach are told to prepare for food by secreting stomach acid.

Perhaps you’ve noticed that when you are stressed, you lose your appetite or are prone to heartburn. This is because your brain is under the influence of the ‘fight or flight’ state – in this state, digestion is not a priority! Blood is shunted away from the digestive tract and towards the skeletal muscle – so that you can quickly flee or summon the reflexes for a fight. Your primitive brain can’t tell the difference between a bear attack and a modern-day stress like an important work meeting. This is an example of the nervous system controlling the gut’s ability to digest food and the subsequent suppression of gastric juices both halts appetite and increases risk of heart burn, bloating, digestive pain and nausea.

How does the gut influence the brain?

We now know that the gut is responsible for the production of over 90% of serotonin, that ‘feel good’ hormone we associate with a positive mood. Hormones produced by the gut are required for signalling other organs and tissues throughout the brain. Essentially neurotransmitters are chemical messengers which are vital for our overall health and mood.

The gut also forms a fair majority (70%!) of the immune system. As the gut is a filter for much of what enters the body, it’s essential that it has a system of identifying what is safe to ingest and what is foreign – this system is the immune system! When your gut cells and microbiota encounter a food, protein, preservative, pesticide or other substance that it recognises as foreign, an inflammatory response is triggered. This serves an important protective function and communicates to the blood that a foreign substance has been identified. Inflammatory chemicals are released and white blood cells are recruited to isolate and deal with the problem.

Whilst this is an essential mechanism, the volume of preservatives, artificial flavourings and inflammatory proteins in the typical western diet means that these responses are being triggered repeatedly, often at every meal. Over time, the lining of our gut (which in parts is only one cell thick!) becomes eroded and inflamed. This becomes a vicious cycle, because when the lining is damaged and inflamed, the immune response is heightened still, and larger proteins and molecules are exposed to our immune system. That thin, semi-permeable one cell lining gets gaps – it becomes leaky.

Why is this important?

Just as there is a specialised lining in the gut to filter what is allowed into the blood stream, there is a similar lining in the brain which filters what is allowed to pass from the blood to the brain. It’s called the blood-brain barrier and when it’s damaged, inflammatory molecules and proteins are able to enter the brain, triggering further inflammation. Inflammation in the brain is one potential model of depression, anxiety, brain fog, concentration, memory issues and other conditions like dementia.

We now know that if the gut is leaky, it is extremely likely that the brain barrier is also leaky. In this way, a damaged gut can be a major contributing factor to anxiety and depression.

What foods contribute to anxiety in this way?

Gluten. Gluten is a protein that when ingested, triggers the release of zonulin. Zonulin causes the gaps between our intestinal cells to open and remain open for a period of time. How long the gaps remain open for varies, depending on genetics. Some people will be more sensitive to the effects of zonulin than others. In this way, gluten actively promotes a leaky gut. As a protein, gluten can also trigger the immune response, causing inflammation in the gut. Interestingly, zonulin has been found to increase the permeability of the blood brain barrier as well, meaning more inflammatory proteins and molecules can get access to the brain, affecting mood.

But what if I feel fine after eating bread and pasta and I’m not coeliac?

There is research that has identified that in some people, the effects of gluten are purely neurological. Meaning that although it doesn’t cause digestive issues, the immune response launched when gluten is encountered by the immune system can present itself in the form of anxiety, depression, brain fog and memory issues. Even if you’re bloat-free. This is in part due to the leakiness of the blood brain barrier caused by zonulin.

So I should just eat gluten free?

Unfortunately, wheat contains hundreds of different proteins that could potentially trigger an immune response. Eating foods that are naturally gluten free is the best option, rather than foods that have had the gluten processed out of them which may contain other proteins or ingredients that irritate the gut lining!

This is a but a short overview of how the gut can contribute to anxiety and other mental health issues. The information in this article is not intended to diagnose or treat, rather provide an opening to a larger conversation that needs to be had regarding gut health, diet and mental health! Wondering how your own digestion might be affecting other areas of your health? The gut is one of my topics of passion, so I would love to help in any way I can. Simply make an appointment by clicking the ‘book now’ button below!

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