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The ‘Brain-Gut Axis’ is a term used to describe the two-way communication system between our digestive tract and the brain. A growing body of research into this axis demonstrates how much influence the gut can have over the brain and vice versa. When we speak about reactions to foods, we most commonly understand them as immediate and often dangerous allergic responses, such as the constriction of the throat and trouble breathing, or dizziness and fainting. It is usually easy to pinpoint the food that causes these reactions because of the immediate immune system response, caused by a type of immune cell known as IgE antibody. In contrast to this, food intolerances are mediated by IgG antibodies and these reactions can take up to 48 hours to have an effect. Symptoms related to IgG reactions can often be manifested as chronic issues like joint ache, IBS and depression or anxiety, which are often overlooked and not associated with what we eat.
Communication between the gut and the brain is controlled via our immune system, our endocrine system (hormones) and our central nervous system, which are all under the influence of the bacteria in our gut. The types and amount of these bacteria, known as our gut microbiome, can be directly impacted by factors such as diet, stress, pollution and medications and the composition of the microbiome is also understood to affect one’s susceptibility to food sensitivities and intolerances.
To understand further about how food intolerances can impact our mental health, it is important to explain the relationship between our gut microbiome, the immune system and our brain in a little more detail. The walls of our digestive tract provide a barrier between what we eat and the rest of our body and an unhealthy gut microbiome can lead to increased levels of inflammation, leaving the walls vulnerable to structural damage. Our intestinal wall is composed of cell junctions that prevent bacteria and large food molecules from entering the bloodstream, however, if these become damaged, proteins from foods that should not be circulating in our bloodstream can enter and an immune response is mounted as a reaction. This response is mediated by IgG, an antibody, that helps to protect against bacterial and viral infections as well as food antigens and is the most abundant immune cell in the body. Whilst food antigens are usually quickly cleared by an intelligent system called the reticuloendothelial system, with structural damage and a poor gut microbiome, this immune response can keep reoccurring. It is suggested that a chronic immune response such as this can have a negative impact on the brain, damaging its own structural barrier, called the Blood Brain Barrier.
The Blood Brain Barrier (BBB) is similar in structure to the intestinal barrier and is usually highly selective, allowing certain required metabolic products, such as short chain fatty acids and amino acids to pass into the brain from our wider circulation but protecting the brain from potentially damaging components. When the BBB is compromised, unwanted translocation may occur such as allowing a bacterial invasion, which can alter the function of immune cells that are responsible for regulating inflammation. Chronic inflammation is associated with many mental and physical health problems, so it is therefore suggested that poor gut health can have a direct correlation to poor mental wellbeing. This is as a result of a compromised intestinal barrier and the negative impact this has on our brain’s own structural barrier (BBB), resulting in inflammation.
Large scale studies have shown the association between chronic low-grade inflammation and depression. For example, in a study that examined data from 14,275 people who were interviewed between 2007 and 2012, they found that people who had depression had 46% higher levels of C-reactive protein (CRP), a marker of inflammatory disease, in their blood samples. Studies like these are paving the way towards a new understanding of the pathology of mental health conditions and how diet and stress can alter bodily systems, such as digestive function and consequently impact mental wellbeing.
Measuring IgG antibodies in food intolerance tests has been implicated as a popular strategy to tackle symptoms related to sensitivities such as IBS, joint pain, fatigue, migraines, anxiety and depression. A recent survey on 708 people commissioned by Allergy UK, demonstrated how 81% of those with elevated IgG levels, as well as psychological symptoms, reported an improvement in their condition after following a food-specific IgG elimination diet. Taking this all into account, health professionals and those with poor mental health may want to consider the potential role of food intolerances in mental well-being and in managing common mood-related disorders, such as depression and anxiety.
Foods that are rich in collagen and its amino acids, like glycine and proline, are great for healing connective tissue, which is what the intestines are made up of. A traditional food, rich in these amino acids, that has made its way into our kitchens again after rediscovering its therapeutic properties is bone broth. Another example of a group of traditional foods that can be used therapeutically in building digestive health, are fermented foods such as kefir, sauerkraut and kimchi. These are abundant in probiotics, which are the ‘good’ bacteria our digestive system needs to help keep a good balance and protect the intestinal barrier from pathogens, toxins and parasites. Once these foods have been introduced on an everyday basis along with eating a healthy nutrient-dense diet and the possible use of supplements to help restore balance, it may be possible to reintroduce foods that were previously triggering an IgG response carefully, one at a time, whilst monitoring symptoms.
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