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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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Attention Deficit and Hyperactivity Disorder (ADHD) is a condition that relates to a collection of behavioural symptoms such as hyperactivity, impulsiveness and inattentiveness. It is most commonly diagnosed in childhood between the ages of 6 and 12 when disruptive behaviour begins to show, however, due to a growing awareness of the condition, it is also becoming common among adults. According to the thinktank Demos, the cost of undiagnosed ADHD in adults in the UK, who are unable to work or hold down a full-time job, are estimated to cost billions of pounds to the nation. They warn that too many may be going through life struggling, unable to access the support or diagnosis they need, which means there could be a huge amount of wasted talent.
The most common front-line of treatment for ADHD is medication and cognitive behavioural therapy (CBT). Prescriptions for ADHD drugs such as Ritalin, have doubled to 922,000 a year in the last decade, and whilst it offers symptom management for many, it has also been found to have significant negative side effects such as weight loss, liver toxicity, and suicidal thoughts, and in the short term may suppress pubertal growth. The aetiology of ADHD is multifactorial, meaning that there are varying influencing factors that drive the symptoms. This is perhaps why this condition has been hard to study and find effective treatment for.
A key area that has been widely researched is the link between the microbiome (bacteria) in the gut and the brain. The hypothesis is that alterations in bacteria due to changes in our environment such as increased hygiene, increased exposure to antibiotics, refined and processed foods and stress, have led to disturbances in short-chain fatty acids (SFCAs), which are byproducts of fermentation in the gut when bacteria come into contact with indigestible fibre found in food.
One SCFA in particular, called propionic acid, has been identified as a driver for abnormal behaviour that is related to both ADHD and the autism spectrum. This SCFA can alter metabolic and immune pathways, as well as gene expression, which can affect the functionality of the brain cells and their receptivity to neurotransmitters, as well as their ability to regenerate and regulate inflammatory responses. Certain strains of pathogenic bacteria, such as clostridia, have been implicated in producing large amounts of propionic acid. This strain of bacteria is naturally present in the gut, however, an overgrowth can occur when good bacteria levels are compromised and/or there is an acute infection. In addition, processed wheat and dairy products often contain propionic acid as a food preservative in the form of calcium propionate.
Other SCFAs such as butyrate, are well known for having health-promoting properties, such as producing anti-inflammatory effects by being able to regulate T-cells (immune cells) in the colon, as well as helping to maintain a healthy gut barrier function. In order to increase the favourable, health-promoting SCFAs, such as butyrate, it’s important to increase the intake of vegetables, fruits and good fats such as grass-fed butter, coconut oil, nuts and seeds, olive oil and avocado. These provide food for gut bacteria to feed on, also known as prebiotic fibres. Foods such as those listed above, contain the right nourishment for gut bacteria to produce SCFAs that support health. Eating traditional foods such as fermented cabbage and other vegetables, as well as bone broth, are also rich in prebiotics and nutrients that support a healthy microbiome and digestive system.
Exposure to toxins and heavy metals has also been implicated in the aetiology of ADHD. Research shows that significant childhood exposure to heavy metals and chemical compounds promotes neurodevelopmental toxicity and may be one of the underlying drivers of behavioural disorders among children.
For example, prenatal exposure to phthalates, which are chemical compounds that are commonly added to plastics to increase their durability and flexibility, have been linked to behavioural abnormalities, characterised by shortened attention span and impaired social interaction. Phthalates are an extensive group of chemicals, and whilst not all of them have been studied, several have shown to have negative health impacts. This class of chemicals is found abundantly and can find their way into food packaging, cosmetics and household cleaners – making them virtually impossible to avoid. However, a growing awareness about the potential negative impact on health has led to the production of phthalate-free cosmetic and personal care products, as well as cleaning products. It may, therefore, be a significant step to try to avoid these chemicals by choosing products wisely, as well as trying to buy vegetables, fruit etc that haven’t been wrapped in plastic.
Mercury exposure is among several other heavy metals, such as lead, aluminium and cadmium, that have been implicated in the aetiology of ADHD. Childhood exposure to mercury is predominantly through the consumption of seafood, dental amalgams and vaccines containing thimerosal. The reason why mercury can be so problematic, as well as other metals, is that it is capable of breaching the blood brain barrier. This is the brain’s ‘high fortress’, an intelligent gateway system that filters through molecules that are needed in the brain such as cells, nutrients and signalling molecules, and filters out pathogens and toxins.
Mercury, as well as other heavy metals such as lead, can accumulate in brain tissue, as well as in the spinal cord, as they are fat-soluble. This means that they can hide themselves in fat tissue, abundant in both the brain and the spine. Once there, they can induce an inflammatory process called oxidative stress, displace important nutrients for brain health, such as zinc and iron, which are essential for neurotransmitter production.
An important dietary step to avoid heavy metal toxicity is choosing seafood and fish that has reduced levels of exposure. The Seafood Watch web page is a fantastic resource that has an extensive list of fish, seafood and sushi products that are safe, as well as those that are best to stay away from. For example, choosing wild pacific caught salmon is safer than Atlantic caught salmon.
The body has its own inherent detoxification pathways that are responsible for packaging and removing heavy metals safely from the system. For example, glutathione is known as the body’s ‘master antioxidant’ and aside from playing an important role in preventing free radicals from causing damage to the body’s cells, it also helps to bind to heavy metals and remove them from the body. Research shows that glutathione levels are lower than normal in those on the autism spectrum, so enhancing levels through the diet may be an effective way to prevent the accumulation of heavy metals. Consuming sulfur-rich foods such as broccoli, cabbage, onions, garlic, kale and cauliflower can boost glutathione levels, as well as milk thistle, which has unique flavonoids that also support glutathione production.
Most water filters on the market only filter out bacteria, parasites and organic compounds. There is a different method to filter out heavy metals, so make sure it explicitly says it does. The reverse osmosis method seems to be the most effective and can be integrated into the kitchen tap.
As mentioned above, eating foods that are rich in indigestible fibre such as vegetables and fruits, as well as eating good fats that are found in grass-fed butter, nuts and seeds, olive oil, coconut oil and avocado, provide bacteria with prebiotics that help to produce the ‘friendly’ short-chain fatty acids, such as butyrate. Avoiding processed foods that contain calcium propionate, which lead to higher levels of propionic acid – the not so friendly short-chain fatty acid – is also another key strategy to support the gut-brain link.
There are many more steps to help support the optimal functioning of the brain and therefore encourage improved learning and development. However, another key strategy to support brain health is to increase intake of omega 3, an essential fatty acid, that is most abundantly found in oily fish such as salmon, mackerel and sardines. Be sure to choose salmon that has had less exposure to polluted water – visit the Seafood Watch web page to find the best sources. Omega 3 is vital for the brain’s function, particularly one of its components called DHA. This is a key building block for the brain and is what keeps neurons (brain cells) working well and supports proper signalling via neurotransmitters.
Lastly, this may seem like a no-brainer, however, avoiding refined sugar and processed foods at all costs is essential for managing ADHD symptoms. These foods have a negative impact on blood sugar levels, which consequently affect mood and concentration.
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