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Estimated reading time: 5 mins

The Gut Brain Axis

The gut microbiome, defined as the bacteria that colonises our digestive tract, seems to be a buzz word at the moment within the health industry, as a growing body of research is showing just how important quantity and quality of protective gut bacteria are for our health. But the most interesting recent discoveries concerning gut bacteria are how they interact with our brain, in a system that has been labelled the gut-brain axis. This axis represents a two-way relationship between the gut and the brain, whereby our bacteria help communicate messages to our brain and neurochemicals communicate from our brain to our gut. Not only have researchers found that gut bacteria are important for gut motility and nutrient absorption, but they are also finding that these 100 trillion microorganisms, that represent around 1000 different species, can actually modulate brain development and activity, as well as playing a role in conditions such as autism.

Autism and IBS

In the UK, there are over 700,000 people who are on the autism spectrum, which is a lifelong condition that can greatly impact the lives of those living with autism and their relatives. Research has continuously shown that those on the spectrum commonly have comorbidities related to digestive function, such as IBS. In a study of 255 (184 males/71 females) children with autism between two and 3.5 years of age and 129 (75 males/54 females) typically developing children in the same age group, it was found that preschool-aged children with autism were 2.7 times more likely to experience GI symptoms than their typically developing peers. Almost 50% of children with autism reported frequent GI symptoms — compared to 18% of children with typical development. It is not yet understood why this is the case, however the research on how our gut microbiome can influence brain activity is providing the grounds for new therapeutic measures for conditions like autism. 

The role of short chain fatty acids

The composition of our gut bacteria and its diversity is often dependent on the food that we eat. Insoluble fibre such as cellulose, xylans and inulin found in foods such as vegetables and whole grains, provide fuel for our gut bacteria to flourish and ferment to create short-chain fatty acids (SCFAs). These fatty acids, produced by protective bacteria, can reduce the production of proinflammatory molecules called cytokines and can enhance anti-inflammatory processes. SCFAs produced by certain strains of bacteria have also been found to be capable of producing neurotransmitters such as GABA, which is an inhibitory neurotransmitter that helps to regulate anxiety. Bacteria can also produce a set of neurotransmitters called monoamines such as dopamine, which helps control the brain’s reward and pleasure centres, serotonin, our mood stabilizer, and noradrenaline, a neurotransmitter that’s involved in our fight or flight stress response. The vagus nerve, which travels from the intestine to the brain, enables neurochemicals produced by the gut bacteria to be signalled to the brain.

SCFAs produced by pathogenic bacteria, such as the Clostridial species, have on the other hand, been shown to be elevated in those with autism. Disrupted gut bacteria has been frequently associated to autism in studies showing unfavourable amounts of pathogenic bacteria in stool samples and in biopsies of children on the autism spectrum. A variety of drivers such as early weaning from breast milk to infant formula, which was related to increased fecal concentrations of SCFAs produced by pathogenic bacteria, and genetic alterations that can negatively impact how food is digested, have been shown to play a role in symptoms associated to autism. 

Stress and the gut

Research has also shown how psychosocial stress can negatively impact our gut, by altering the composition of gut bacteria and thereby increasing inflammation. This is further evidence for the two-way relationship that exists between the brain and the gut, whereby externally-perceived stress can have a direct influence on the health of our digestive tract. A study measuring lactic acid bacteria (protective bacteria) in college students undergoing the stress of final examinations, found a significant decrease in this type of bacteria after the examination. In addition, studies observing the behaviour of bacteria-free mice, showed a wide range of deficits in brain and gut biochemistry, social behaviour and stress responses compared to mice inoculated with gut bacteria, again giving strong evidence for the role of gut bacteria in modulating brain activity. 

In children with autism, the presence of dysfunction in the gastrointestinal tract is commonly associated with aggressive behaviour, tantrums, anxiety, irritability and sleep disturbances. Research on probiotics (supplements containing protective bacteria) and their beneficial effect on gastrointestinal conditions such as irritable bowel syndrome and diarrhea, is well-established. Considering this, it is not surprising that the use of probiotics as an integrative therapeutic approach to autism, is now being extensively investigated. Although the exact mechanism of how probiotics can modulate behaviour and mood in those with autism is not yet fully understood, researchers have posited that this may be due to how protective bacteria target circulating neurotransmitters and neuroimmune responses within the gut-brain axis. Probiotics have been found to reduce certain metabolites that have been associated to autism and gastrointestinal symptoms that are strongly correlated with the disorder. 

Moving towards a personalised approach

Achieving optimal nutrient intake is additionally more difficult for those with autism. This is due to a higher rate of food allergies and/or intolerances to certain foods such as dairy, nuts and wheat, as well as a tendency to towards picky eating and food selectivity. There is no one-size-fits-all diet that is right for everyone, each person is biochemically unique, with a variety of genetic, environmental and lifestyle factors that can influence health, which is why it is important to work with a trained professional. However, there are certain key dietary factors that have shown to be beneficial for those on the autism spectrum, which you can begin integrating into your child’s or your everyday life now. If you’d like to see these steps, click here to go through to our Nutrition Solutions page on Autism. 

The British Association of Applied Nutritional Therapists (BANT) has a register for qualified Nutritional Therapists in Britain. The Brain Bio Centre, our not for profit clinic, offers face to face in London and Skype appointments to enable consultations from across the UK and overseas.

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