• Science Fueling Fitness

Our Second Brain: Gut Microbiome, Mood and Food


They are on you. They are in you. The trillions of organisms on our skin and inside our guts are known as the microbiota. Specifically, here we are talking about the gut microbiome. Composed mainly of bacteria, but also consisting of fungi and viruses, these microbes have more genes than the human in which they are living. Technically, we are a colony of bacteria surrounded by a human body! Emerging scientific evidence has linked the microbiome to metabolic diseases such as obesity and even diseases of the brain such as depression and anxiety. Imagine there is a simplistic way, aside from anti-depressants, to manage anxiety disorders and depression. Imagine the impact that would have on the person - creating a healthful way they can live their life while simultaneously creating an optimal gut environment to prevent the onset of diseases. Sounds too far fetched to be true, right? Well let's examine the evidence.

There is a communication between the gut and the brain known as the gut-brain axis. Within this axis, the gut microbes have the capacity to influence specific brain and neuronal processes, ultimately influencing mental health. This communication means the gut is like a 'second brain'. Imagine if the composition of our gut microbiota, (modifiable through diet), could impact on our mental health… There is now sound evidence to prove that a strong link exists between the bacteria residing in our intestines and the development of disorders such as depression and anxiety. One example of this is that patients who are diagnosed with major depressive disorder have a significantly altered microbiome than those without the condition. Those patients with major depressive disorder have a lot more Bacteroidetes, Actinobacteria and Protobacteria and less Firmicutes and Faecalibacterium. More notably, with even greater levels of depression, even lower levels of Faecalibacterium are seen [1]. This means that, potentially, through the promotion of some of these good gut bacteria, such as Firmicutes, we may be able to offset this condition.


Another condition, called generalized anxiety disorder, has also been linked to dysregulated gut microbial composition. Recent evidence suggests that Faecalibacterium, Lachospira, Sutterella, Butyricicoccus and Eubacterium Rectale were significantly fewer in patients suffering from this disorder [2]. Perhaps this could be because these particular bacteria are strong producers of Short Chain Fatty Acids (SCFAs) such as butyrate, acetate and propionate. These SCFAs have a reported range of benefits throughout the body, including improved metabolism within tissues such as the adipose tissue, the liver and the skeletal muscle. Why don't we cut to the chase and supplement with SCFAs then? You can supplement with butyric acids but these acids will be absorbed in the small intestine and never make it to the gut, where it is hypothesized that they exert their effects. How do we increase our SCFAs then? It has been shown that ingesting fibre is a much more practical way to gain the benefits of these SCFAs.


Dysregulation of the gut, termed 'dysbiosis', is where certain micro-organisms are missing/absent and others are highly populated within the gut. Dysbiosis through antibiotic administration in mice has presented an intriguing causal role for the role of gut microbiota and depression. After the antibiotic treatment, the animals displayed depression-like symptoms and altered hippocampal firing. For those of you just getting over your latest dose of antibiotics though, have no fear as these effects were reversed following a probiotic treatment with Lactobacillus casei DG [3]. Improvements in the gut microbial composition are potentially influenced by prebiotics and probiotics. Prebiotics are those compounds which are ingestible, such as fibre, and stimulate the gut to produce beneficial bacteria, whereas probiotics are ingestible products containing viable micro-organisms which will alter the microbiota composition through colonisation.


Since 2005, researchers at University College Cork, Ireland, have been trying to establish the gut-brain axis theory. Professor John Cryan and Professor Ted Dinan have conducted research aiming to determine how the food we eat impacts out gut and thereby interacts with our brain and mental health. Their book ‘The Psychobiotic Revolution’ has been hailed a worldwide success and is a step in the right direction regarding the treatment of patients with depression. Professor Dinan delves into the prospective alterations in therapy:


“For so long it’s generally been perceived that anti-depressants and cognitive behavioural therapy are the mainstay of treating depression but our work clearly shows that your microbiota is very important and that for a more holistic management of depressive illness we should be focusing on diet and exercise as well.”


So with the aforementioned research in mind, the question becomes; how can we alter our gut microbiome? Isn’t it completely formed at birth and through breastfeeding? Is it our mothers who have the main stake in the formation of a richly diverse gut microbiome protecting us from disease and ill health? In part yes. Our gut microbiota is formed in the first three years of life, however, it can indeed be altered to favour a more diverse or an assorted range of gut bacteria.


As mentioned, when prebiotics such as fibre are ingested they have a positive impact on the naturally residing good bacteria in your gut. So what is fibre? We know some foods are high in fibre, we know we need fibre in our diet but do we actually know what fibre is? Dietary fibres are large carbohydrates, much bigger than glucose. Fibre isn’t digested or absorbed in the intestine and can be either naturally occurring fibre or synthetically produced. Different foods contain different fibres. For example, a banana contains an inulin-type fructan whereas an apple is a source of a fibre known as pectin. This is why a diet richly diverse in a range of fruit and vegetables provides us with a good assortment of dietary fibres! As the bacteria in our gut breakdown or ferment these dietary fibres, we get the production of these SCFAs, in turn improving insulin sensitivity and fatty acid breakdown in the body. Highly fermentable fibres such as β-glucan (found in oats) and pectins, are fibres reported to have a range of health benefits alongside SCFA production. Bifidobacteria and lactobacilli, gobble up fructan and are referred to as lactic acid bacteria because they produce lactate and acetate. These substances can then be used by other bacteria such as Eubacterium, Roseburia, and Faecalibacterium, which then release butyrate. This all very sciencey stuff just means that the more varied our diet is in terms of fruit and vegetables, the more varied our bacteria will become and the more health promoting effects will take hold!


But hey, what if I have no good gut bacteria in my gut? What if I was on antibiotics and I fear for the worst? How can I heal my gut microflora to ensure only good gut bacteria reside thereby promoting anxiety relief and a good mood? One word: Probiotics. Live yogurt (you can find it in most supermarkets) is a great source of good bacterial cultures. If you’re feeling adventurous, kefir (fermented milk) is a wonderful probiotic yogurt drink. Kimchi, Sauerkraut and Kombucha – all other sources of probiotics whose aim is to distribute healthy bacteria to the gut where they can reside, grow and flourish.


So where can I start? It is recommend you start by getting seven portions of fruit and vegetables a day. Eat the rainbow! Ensure your diet is based around a glorious ensemble of fruit and veg followed by wholegrains, dairy and meats. It is recommended you aim to eat as much plant-based produced as possible, and to ensure the colour palette is richly diverse. These plant-based products not only include carrots and celery etc. but also include beans, grains, rice and oats. Within two weeks, a healthy gut can be promoted to a healthier phenotype. And if you are into a more rapid approach, there’s always faecal transplant! Watch this space…


  1. Jiang, H., Ling, Z., Zhang, Y., Mao, H., Ma, Z., Yin, Y., … Ruan, B. (2015). Altered fecal microbiota composition in patients with major depressive disorder. Brain, Behavior, and Immunity, 48, 186–194. https://doi.org/10.1016/j.bbi.2015.03.016

  2. Jiang, H. Y., Zhang, X., Yu, Z. H., Zhang, Z., Deng, M., Zhao, J. H., & Ruan, B. (2018). Altered gut microbiota profile in patients with generalized anxiety disorder. Journal of Psychiatric Research, 104, 130–136. https://doi.org/10.1016/j.jpsychires.2018.07.007

  3. Guida F, Turco F, Iannotta M, De Gregorio D, Palumbo I, Sarnelli G, et al. . Antibiotic-induced microbiota perturbation causes gut endocannabinoidome changes, hippocampal neuroglial reorganization and depression in mice. Brain Behav Immun. (2018) 67:230–45. 10.1016/j.bbi.2017.09.001

#GutMicrobiome #Probiotics #Prebiotics

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