By Dr Chia Boon Tat
THE SECRET TO BRAIN HEALTH LIES IN OUR GUT
Embedded in the wall of our gut, lies a complex nervous system comprising an estimated 500 million neurons. Sometimes called the “Second Brain”, this enteric nervous system (ENS) can work independently of and in conjunction with the brain in our heads. Although it is not capable of cognitive thoughts, it is capable of “thinking”, “remembering” and “learning”, and accounts for our emotional and mental health.
Information flows back and forth continuously between the brain and our gut via an information expressway, called the gut-brain axis. An example of the gut-brain connection at work is the sinking feeling we get in the pit of our stomach during a stressful event. So is the “gut feeling” when meeting somebody for the first time or relying on “gut instinct” when faced with making a difficult decision.
The brain can control environmental conditions in the gut such as the rate at which food is being moved and the amount of mucus lining the gut. This has a major impact on our gut microbiome – the 100 trillion bacteria of several thousand species living in the gut. These microbes perform beneficial functions such as food digestion and making vitamins. They play a fundamental role in our immune system and constitute the first line of defence against pathogens. The gut microbiome can modify very rapidly when adjusting to change in diet or a stress-induced decrease in gut transit time. Through the gut-brain axis, the gut microbes inform the brain of the changes and eventually influence our mind: shaping our perception of the world and altering our behaviour[ii].
The communication between the brain and gut uses more than 30 neurotransmitters (brain chemicals), most of which are biochemically-identical to those found in the brain. The gut microbiome directly influences the levels of these neurotransmitters. For example, it is estimated that our gut produces 50 per cent of dopamine and over 90 per cent of the serotonin in the body[iii]. These neurotransmitters regulate our mood, and recent studies have linked their deficiency to the onset of neurological disorders including anxiety, depression, ADHD, ADD and autism spectrum disorder. Although these neurotransmitters do not enter the brain (the brain synthesizes its own neurotransmitters), they do provide an indication of our emotional and mental health.
DYSBIOSIS, INTESTINAL PERMEABILITY AND NEURODEVELOPMENTAL DISORDERS
In the modern day, our gut microbiota is subjected to constant assault from eating processed foods, taking drugs & antibiotics, living with stress and usage of disinfectants. This depletion of gut microbes, called dysbiosis, compromises the integrity of the gut lining, causing intestinal permeability (often called “leaky gut”) through which toxins, pathogens and undigested food particles may leak into the blood stream, triggering responses from the immune system which eventually cause chronic inflammation to occur throughout the body. The chronic inflammation may in turn lead to the development of diseases such as metabolic disorders (type 2 diabetes, obesity, hypercholesterolemia, malnutrition), neurodevelopmental disorders (anxiety, depression, ADHD, ADD, autism spectrum disorder, dementia) and autoimmune disorders (irritable bowel disorder, eczema, food sensitivities and other allergies).
Fortunately, disrupted gut microbiota can be re-balanced, and subsequently health be restored. Studies have shown that beneficial bacteria are able to restore and maintain the health of intestinal gut walls, thus repairing the “leaky gut” syndrome and reducing inflammation in the body.
Studies have shown that people suffering from neurodevelopmental disorders lack certain types of microbes in their gut[iv]. In another landmark study on brain development, a team from Caltech found that when the guts of autistic mice are rebalanced with specific bacteria, their autistic behaviours are reversed[v]. Numerous studies have also associated gut bacteria with influencing mood, behaviour and brain function[vi].
A DIET FRIENDLY TO GUT MICROBES CAN MAINTAIN GOOD MENTAL HEALTH
Eating foods which contribute to the well being of our gut microbes is an essential factor for maintaining mental health.
It is important to include in our diet foods rich in prebiotic and probiotics. Prebiotics are plant fibres that cannot be digested by the human body. They nourish the good bacteria (Bifidobacteria & Lactobacilli ) already present in the colon. Examples of foods rich in prebiotics are garlic, onions, asparagus, bananas, cabbage, beans and legumes.
Probiotics are “good” bacteria that help keep your digestive system healthy by controlling growth of harmful bacteria. Probiotics can be found in fermented foods such as kimchi, tempeh, yoghurt and sauerkraut. For example, in fresh cabbage, vitamin C is bound in the cellulose structure and various other molecules, and our digestive system is just not able to cleave it off and absorb it. Lots of it goes undigested and come out right out of the body. So despite the fact that cabbage may be very rich in vitamin C, a lot of it will not be able to absorb. But if that cabbage is fermented to make sauerkraut, all the vitamin C becomes bioavailable. The amount of bioavailable vitamin C in sauerkraut is 20 times higher than in the same helping of fresh cabbage. Probiotics can also be taken as supplements. However, not all probiotic supplements are specific for ADHD, and care must be taken to choose those which can survive and thrive in the gut environment.
[ii] Gut-brain link grabs neuroscientists, Nature, 12 Nov 2014.
Can be accessed at http://www.nature.com/news/gut-brain-link-grabs-neuroscientists-1.16316
[iii] Microbes help produce serotonin in gut, Caltech, 9 Apr 2015.
Can be accessed at https://www.caltech.edu/news/microbes-help-produce-serotonin-gut-46495
[iv] Study: Kids with autism have fewer kinds of gut bacteria, Autism Speaks, 3 Jul 2013.
Can be accessed at https://www.autismspeaks.org/science/science-news/study-kids-autism-have-fewer-kinds-gut-bacteria
[v] Bacterium can reverse autism-like behaviour in mice, Nature, 5 Dec 2013.
Can be accessed at http://www.nature.com/news/bacterium-can-reverse-autism-like-behaviour-in-mice-1.14308
[vi] The tantalizing links between gut microbes and the brain, Nature, 14 Oct 2015.
Can be accessed at http://www.nature.com/news/the-tantalizing-links-between-gut-microbes-and-the-brain-1.18557
This articles was first published in “I’m not naughty”, pp 8-9, issue 38, April 2016. This is a newsletter of SPARK, the society for the promotion of ADHD research and knowledge based in Singapore. Click here to view the original article and newsletter.