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The microbiome and the gut-brain axis

160628_TSF_BlogHero_01We have discussed the microbiome a couple of times here on the That Sugar blog, because it is darn-well fascinating!

The state and diversity of the microbial population of our guts can have profound impacts on health and happiness. And science is delivering new fun facts on this topic all the time.

And it seems that what goes on in the gut can heavily impact your mood, behaviour and brain.

The brain-gut connection

The brain and the gut are intrinsically linked via the nervous system. In fact, the gut is considered a second brain.

There are more nerves in the gut that in the spinal cord. Whoa! Feel those butterflies in your belly? That is anticipation, worry, nervousness, or intuition – all linked to the vagal nerve running along the spine, and the brain’s survival instinct!

Then, considering the wonderful connection between the brain and the gut, surely the health of the microbiome will influence mental health and how the brain and nervous system function, right?

The gut-brain axis and gut bugs

The gut-brain axis is a two way network that links the gut and the emotional and cognitive centres of the brain. It also encompasses the endocrine, nervous and immune systems.

Pretty significant, especially as the gut-brain axis has been shown to influence genetic and the environmental effects on brain development and function! 6

The brain can impact the health of your gut. Feelings of fullness and hunger registered by your brain, and the types of food and whether we have food in our intestines affects what the gut bugs are doing, and which are thriving or dying.

Ever need to dash for the loo when you are feeling nervous? Um, yeah.

Stress is a big factor in influencing microbial composition and negatively impacting the ability to perform protective functions, resulting in things like leaky gut.5

Then we have the intestinal microbiome.

The presence and balance of microbes within our intestine can have significant influence on the brain, mood and behaviour. They also regulate inflammatory pathways (and inflammation itself has a major role to play in brain and nervous system function!).6

It is thought the microbiome of a newborn plays an integral role in the development of the nervous system, and also whether someone will experience significant degradation of the nervous system in old age.

In fact, a correlation has been found between reduced diversity of microbes in the aging adult with a decline in sensory, motor and cognitive function. This may be due to reduced short chain fatty acid (SCFA) production, increased levels of inflammation, and less bioavailability of anti-inflammatory and brain supportive polyphenols found in whole plant foods.6

Image credit:
Image credit:


Microbiome, brain, mood and behaviour

The lack of diversity in the microbial population, and the integrity of the intestinal wall – which is maintained with a healthy, flourishing microbiome – may influence negative symptoms and disease such as depression, anxiety, autism and Parkinson’s disease.3

Gut bacteria may also impact teen behaviour,2;3 and appears to influence levels of mood modulating neurotransmitters, such as dopamine, GABA, histamine, acetylcholine and serotonin.6

What is interesting, is diet seems to have powerful sway over the state of balance (symbiosis), or imbalance (dysbiosis) of the microbiota, and therefore our mental and brain health.1

Diet, food and our gut bugs

What we eat can influence what flourishes and what dwindles away within our intestinal microbiome.

From fibre, our gut bugs synthesize SCFA, such as acetate, proprionate or butyrate. They are the main source of fuel for colonocytes – the intestinal cells, and also implicated in stimulating the sympathetic and autonomic nervous systems, and modulating brain development and behaviour.

SCFA also play a role as signaling molecules (with positive impacts on insulin, glucose and fat metabolism) and maintaining the integrity of the blood brain barrier.

Therefore, we could say eating fibre can contribute to brain health! We need this bacterial by-product to make sure nasties don’t get into the brain space and wreak havoc.

Dietary choice can influence not only production of SCFA, but also the balance of species of intestinal bacteria. And the behavioural outcomes found are very interesting indeed:

  • High sucrose consumption can lead to increased anxiety, deceased learning, reduced short and long-term memory.6 Yet another reason to kick the sugar!
  • A high-fibre diet compared with the highly processed Western diet has seen greater diversity in microbial species. The Western style diet is associated with increased anxiety, reduced plasticity, and decreased SCFA. High intake of heavily processed fats and carbohydrate foods, with little whole plant foods, has been linked to increased gut permeability and numbers of the not-so-helpful Firmicutes bacterial population. So it is important to eat your veg!
  • Meat containing diets, in balance with fibre and phytonutrient rich plant foods, seem to encourage diversity, memory and reduce anxiety.

Plants are particularly important. It has been found a diet supplemented with prebiotic foods, like leeks, Jerusalem artichoke, chickpeas and more reduces anxiety! Magnesium is also found in plant foods, and deficiency is associated with anxiety-like behaviour.

Then there are the polyphenol* phytonutrients, which have been found to be particularly helpful acting as an antioxidant and anti-inflammatory, and loved by gut bugs.3;6

Eating seasonally and mixing up what fills our plate seems to encourage greater microbial diversity. Which is good, as a greater range of bacterial species, as well as not overeating, are each associated with increased neurogenesis and cognitive ability.

So enjoy variety, and eat real food, not too much, mostly plants (thank you, Michael Pollan).

A healthy microbiome

Whilst research on the microbe-gut-brain axis is in its infancy, consider including a diverse array of foods, as well as consuming an abundance of prebiotic and polyphenol rich* goodies, for long-term support of good mental health.3

In amongst this, we need to consider antibiotics and other deleterious factors that negatively impact the harmony of the microbiome. It has been shown that antibiotic treatment has been associated with anxiety, depression, panic and delirium, even after one course.6 Therefore use only when required!

The microbiome is wonderful yet complex and a burgeoning area of science. Working with our gut bugs is paramount to good health, and can influence weight, type 1 diabetes, immune function, and even the long-term health of your kid-lets.

Feed your gut bugs, and they will work to protect you from short and long-term ills. Happy days!


*Want to know what foods are high in polyphenols?

Try herbs like oregano, peppermint, sage and rosemary, spices such as cinnamon, star anise, and clove, and yes, cacao and dark chocolate (though lose the sugar – that will negate the point!). Polyphenols are also abundant in most veg and fruit.4

By Angela Johnson (BHSc Nut. Med.)



  1. Kennedy, PJ, Murphy, AB, Cryan, JF, Ross, PR, Dinan, TG, & Stanton, C 2016, ‘Microbiome in brain function and mental health’,Trends in Food Science & Technology, [ePub].
  2. Neufeld, KM, Luczynski, P, Oriach, CS, Dinan, TG, & Cryan, JF 2016, ‘What’s bugging your teen?—The microbiota and adolescent mental health’, Neuroscience and Biobehavioral Reviews, [ePub ahead of print].
  3. Oriach, CS Robertson, RC, Stanton, C Cryan JF Dinan, TG 2016, ‘Food for thought: The role of nutrition in the microbiota-gut–brain axis’, Clinical Nutrition Experimental, vol. 6 , pp. 25 – 38.
  4. Pérez-Jiménez, J, Neveu, V, Vos, F, & Scalbert, A 2010, ‘Identification of the 100 richest dietary sources of polyphenols: an application of the Phenol-Explorer database’, European Journal of Clinical Nutrition, vol. 64, pp. S112-S120.
  5. Petra, AI, Panagiotidou, S, Hatziagelaki, E, Stewart, JM, Conti, P, & Theoharides, TC 2015, ‘Gut-Microbiota-Brain Axis and Its Effect on Neuropsychiatric Disorders With Suspected Immune Dysregulation’, Clinical Therapeutics, no. 5, p. 984.
  6. Rogers, GB, Keating, DJ, Young, RL, Wong, M, Licinio, J, & Wesselingh, S 2016, ‘From gut dysbiosis to altered brain function and mental illness: mechanisms and pathways’, Molecular Psychiatry, vol. 21, no. 6, pp. 738-748.
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