What’s your gut got to do with your brain? (Part 1)

Let’s talk about brain health and what your gut has to do with it. We’ve known for a long time that stress can impact on the gut in disorders such as Irritable Bowel Syndrome (IBS). However, new research shows how the gut impacts the brain, and the role it plays in anxiety and depression (1).

The gut and the brain communicate with one another and this is called the gut-brain axis. The collection of micro-organisms living in the gut (such as bacteria, yeast and parasites) is known as the gut microbiome. The gut microbiome is thought to be a key player in modulating our moods via its communication with the brain.


“Our hormones, immune function, brain function and response to stress are all influenced by the gut microbiome (1). And all of these factors play a role in anxiety and depression”


In Part 1 of this blog post, I’ll discuss how the brain and gut communicate, how gut bacteria influence the brain and the evidence for particular strains of bacteria and their effect on mood and behaviour.

In Part 2, I discuss the factors that impact the gut microbiome negatively and what we need to consider in order to support a healthy gut and healthier moods and behaviour.


“Understanding the gut-brain-axis may prove to be pivotal in developing new approaches to brain- and behaviour-related disorders”



How do the gut and brain communicate?


The gut has its own nervous system known as the enteric nervous system and this provides a physical connection to the brain via the vagus nerve. The brain and gut are also chemically connected via hormones, immune cells and neurotransmitters that can travel to the brain via the bloodstream or nervous system (2).

The gut microbiome weighs around 1-2kg, equating to trillions of micro-organisms living in the human body (1).

Microbial genes outnumber human genes by 100 times and they play a central role in energy production, immunity, hormone balance, metabolism, digestion, detoxification and the production of nutrients (3).  The micro-organisms living in the gut affect the communication between the gut and the brain via different mechanisms which I will explore.


How do gut bacteria influence the brain?


Gut bacteria can respond to and produce the same neurotransmitters (chemical messengers) like the ones used by the brain (4) (5):

  • Serotonin: the happy neurotransmitter
  • GABA (gamma-aminobutyric acid): the calming neurotransmitter
  • Dopamine: the reward and pleasure neurotransmitter
  • Acetylcholine: the neurotransmitter involved in muscular contractions
  • Noradrenaline: the stimulating neurotransmitter which raises blood pressure and heart rate

These neurotransmitters can impact on both gut and brain function alike.

Gut bacteria can also produce anti-inflammatory or pro-inflammatory immune messengers that can impact on brain function. Increased inflammation is seen in depression (2).

Inflammation caused by certain types of micro-organisms in the gut can also trigger the body’s stress response, triggering the release of cortisol (6). Cortisol is one of the body’s main stress hormones involved in anxiety.

To sum up, the gut microbiome influences the brain via the production of neurotransmitters, inflammation and stress hormones which can travel to the brain via the bloodstream or the nervous system.


“Inflammation in the gut can lead to inflammation in the brain, aptly named “brainflammation”



Gut bacteria and anxiety and depression: the research


Lactobacillus and Bifidobacterium are the main microbial species living in the gut (2). Supplements containing probiotics (beneficial bacteria) with these species have become popular in recent years due to their numerous health benefits.

“Psychobiotcs” are probiotics that are able to produce neurotransmitters and modulate inflammation. They have mind-altering effects, reducing depression, anxiety, stress and improving cognitive function” (2).

There are specific strains of bacteria that have been found to be beneficial for anxiety and depression, such as:

  • Bifidobacterium Infantis, Lactobacillus Reuterii and Lactobacillus Breve (7) (8) (1) reduce anxiety-like behaviour
  • Lactobacillus Rhamnosus reduce cortisol, anxiety-like behaviour and depressive behaviour (9)(1)(10).
  • Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 improve resilience to stress and emotional responses in healthy subjects (1) and also lower anger, depression and anxiety (11)
  • A probiotic (containing Bifidobacterium bifidumW23, Bifidobacterium lactis W52, Lactobacillus acidophilus W37, Lactobacillus brevis W63, Lactobacillus casei W56, Lactobacillus salivarius W24, and Lactococcus lactis W19 and W58) taken over a period of 4 weeks reduced reactivity to sad mood (12)

Furthermore, prebiotics (foods that feed healthy bacteria in the gut) have been shown to lower waking cortisol (13), a marker of stress.

Fermented foods like sauerkraut and fermented milk drinks can promote the growth of beneficial bacteria (14) and appear to influence brain activity.

From this research, we can clearly see how central the gut microbiota is in managing our moods and behaviour.

So how do we improve our gut bacteria to improve our moods and reduce stress, depression and anxiety?

Well, it turns out there are a lot of different ways to regulate our gut bacteria! Don’t rush out to buy a probiotic just yet.

Head over to Part 2, where you can read about the different factors that impact the gut microbiome that may be contributing to anxiety and depression, and what we need to consider to rebalance our gut bacteria to support our moods, including diet, lifestyle and much more!


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  1. Rea, K., Dinan, T.G. and Cryan, J.F., 2016. The microbiome: A key regulator of stress and neuroinflammation. Neurobiology of Stress, [online] 4, pp.23–33. Available at: <http://dx.doi.org/10.1016/j.ynstr.2016.03.001>.
  2. Misra, S. and Mohanty, D., 2017. Psychobiotics: A new approach for treating mental illness? Critical Reviews in Food Science and Nutrition, [online] 0(0), pp.1–7. Available at: <https://www.tandfonline.com/doi/full/10.1080/10408398.2017.1399860>.
  3. Clemente, J.C., Ursell, L.K., Parfrey, L.W. and Knight, R., 2016. The Impact of the Gut Microbiota on Human Health: An Integrative View. HHS Public Access. Cell, 148(6), pp.1258–1270.
  4. Galland, L., 2014. The Gut Microbiome and the Brain. Journal of Medicinal Food, [online] 17(12), pp.1261–1272. Available at: <http://online.liebertpub.com/doi/abs/10.1089/jmf.2014.7000>.
  5. Lyte, M., 2013. Microbial Endocrinology in the Microbiome-Gut-Brain Axis: How Bacterial Production and Utilization of Neurochemicals Influence Behavior. PLoS Pathogens, 9(11), pp.9–11.
  6. Carabotti, M., Scirocco, A., Maselli, M.A. and Severi, C., 2015. The gut-brain axis: Interactions between enteric microbiota, central and enteric nervous systems. Annals of Gastroenterology, 28(2), pp.203–209.
  7. Nishino, R., Mikami, K., Takahashi, H., Tomonaga, S., Furuse, M., Hiramoto, T., Aiba, Y., Koga, Y. and Sudo, N., 2013. Commensal microbiota modulate murine behaviors in a strictly contamination-free environment confirmed by culture-based methods. Neurogastroenterology and Motility, 25(6), pp.521–528.
  8. Mackos, A.R., Eubank, T.D., Parry, N.M.A. and Bailey, M.T., 2013. Probiotic lactobacillus reuteri attenuates the stressor-enhanced severity of citrobacter rodentium infection. Infection and Immunity, 81(9), pp.3253–3263.
  9. Bravo, J.A., Forsythe, P., Chew, M. V., Escaravage, E., Savignac, H.M., Dinan, T.G., Bienenstock, J. and Cryan, J.F., 2011. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences, [online] 108(38), pp.16050–16055. Available at: <http://www.pnas.org/cgi/doi/10.1073/pnas.1102999108>.
  10. Sarkar, A., Lehto, S.M., Harty, S., Dinan, T.G., Cryan, J.F. and Burnet, P.W.J., 2016. Psychobiotics and the Manipulation of Bacteria–Gut–Brain Signals. Trends in Neurosciences, [online] 39(11), pp.763–781. Available at: <http://dx.doi.org/10.1016/j.tins.2016.09.002>.
  11. Messaoudi, M., Lalonde, R., Violle, N., Javelot, H., Desor, D., Nejdi, A., Bisson, J.F., Rougeot, C., Pichelin, M., Cazaubiel, M. and Cazaubiel, J.M., 2011. Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects. British Journal of Nutrition, 105(5), pp.755–764.
  12. Steenbergen, L., Sellaro, R., van Hemert, S., Bosch, J.A. and Colzato, L.S., 2015. A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood. Brain, Behavior, and Immunity, 48(April), pp.258–264.
  13. Schmidt, K., Cowen, P.J., Harmer, C.J., Tzortzis, G., Errington, S. and Burnet, P.W.J., 2015. Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers. Psychopharmacology, 232(10), pp.1793–1801.
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