gut brain link connection probiotics microbes bacteria


I’ve been making my own yogurt on and off for years (didn’t take me for a hippy did you?) I’m a kiwi and many families have an EasiYo system.  Well, system makes it sound way fancier than it actually is … I just pop the culture mix and water into a jar, and then put that into an insulated yogurt maker … leave it to culture overnight and voila – yummy fresh yogurt complete with billions of probiotic microbes to boost my gut health.

There are plenty of reasons why probiotics are good for you – we need a delicate balance of good bacteria in our intestines to maintain healthy metabolism,  immune function and digestion. But the crucial role that gut bacteria play in the health of our brains is something I never knew about until recently.

Two Irish neuroscientists John Cryan and Timothy Dinan (love the Irish!), recently wrote a review of the neuroscience of the gut-brain connection in Nature Reviews Neuroscience (note: this is a high quality neuroscience publication) and the message they conveyed really surprised me…

Gut microbiota communicate with the brain — possibly through neural, hormonal and immune pathways —to influence brain function and behaviour

An overview of the gut-brain connection

  • a healthy balance of gut bacteria contributes to normal behaviour, cognition, emotion and a well-functioning immune system.
  • poor balance of the bacteria (perhaps brought on by stress, disease or antibiotics) disrupts the gut-brain signalling pathways.
  • disruptions in gut-brain signalling may lead to abnormal brain function, changes in our behaviour, thoughts, emotions, our perception of pain, and may also impact our immune system.

Everyone has a different composition of good gut bacteria, but there are three typical communities (enterotypes) with each community is made up of a single microbial genus: Bacteroides spp., Prevotella spp., or Ruminococcus spp. The food we eat is one of the main factors that can affect the composition of these populations

Fascinating fact alert – our gut is inhabited by 10 times more bacteria than there are cells in our entire body?!

Gut microbiota and brain health


The hypothalamic-pituitary-adrenal axis in the brain is a circuit that controls reactions to stress (as well as regulating functions like digestion, the immune system, mood and emotions).  Chronic stress affects gut bacteria composition, and in return, gut bacteria directly influence the development of the brain’s appropriate stress response.


Both the central and peripheral nerve pathways that sense visceral (abdominal pain) can be affected by intestinal microbes.  Some strains of Lactobacilli and Bifidobacteria can alleviate the pain caused by irritable bowel syndrome and stress.

Multiple Sclerosis:

MS is a devastating autoimmune disease that is characterised by the progressive deterioration of neurological function. Gut bacteria may have a role in the development of MS.

Depression and anxiety:

The neuroscience of gut health and more serious mood disorders is very new, but Profs Cryan and Dinan suggest that as our understanding grows, modulation of the gut microbes may become part of a strategy for developing treatments for complex brain disorders. They have found that brain levels of serotonin, the ‘happy hormone’ are regulated by the amount of bacteria in the gut during early life.

What about probiotics and the gut-brain axis?

Probiotics are live organisms that, when eaten in adequate quantities, exert a health benefit. There is a reasonable amount of clinical evidence supporting the use of probiotics.   In lab animals, probiotics have been shown to reduce anxiety- and depression-like behaviours and prevent stress-induced increases in the stress hormone cortisol.

And, if you’re particularly interested in neuroscience (and of course you if you’re still reading!) probiotics can alter the expression of BDNF levels (a brain chemical involved in neuron growth) and GABA receptors (a type of ‘lock’ that brain chemicals latch onto)

At the end of the paper Profs Cryan and Dinan conclude….

…it is becoming increasingly apparent that behaviour, neurophysiology and neurochemistry can be affected in many ways through modulation of the gut microbes…


Cool huh?  I’m off to make some yogurt.

Cryan JF, Dinan TG. Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nat Rev Neurosci. 2012 Oct;13(10):701-12


What about you?  Do you take probiotics for your gut health

19 Responses to One billion reasons probiotics protect your brain

  1. Hi Sarah. What an interesting post. I have been interested in how nutrition affects the brain for some time now and have followed how irritable bowel syndrome seems to have an association with anxiety (although in which direction is anyones guess). The probiotics side of things adds another dimension because there is some evidence for probiotics helping to manage the symptoms of irritable bowel syndrome in some people, and if it also helped to decrease stress and regulate emotion then that would be a very interesting interaction. Did the paper you are referring to indicate whether the probiotics have direct effects via neuropeptides or other neurotransmitters, or are they perhaps stimulating the brain via activation of the sensory aspects of the vagus nerve? Very curious indeed.

    • Hi Glenda. Thanks for reading!
      The authors did talk quite a bit about the specific methods of communication between bacteria and the brain. One of these ways is via the vagus nerve, but there are also vagal-independent methods of interaction…e.g. the byproducts of bacterial metabolism or bacterial cell wall sugars can directly effect the intestinal wall and reduce inflammation, and activate both the innate and adaptive immune systems. Innate immune system activation can result in alterations in the circulating levels of pro-inflammatory and anti-inflammatory cytokines that directly affect brain function.
      In the case of IBS they postulate that probiotics may be dampening down of the effects of pro-inflammatory cytokines and oxidative stress, coupled with modifications in nutritional status, and they also discuss evidence for probiotics directly impacting in neuronal firing rates.
      You should check the paper out – I’ve linked to a pdf version.

  2. This is fascinating information. I have often wondered if non-dairy yogurts have the same benefits. I have a milk allergy that causes hives if I eat too much yogurt (although it rarely stops me from overdoing it).

  3. I don’t make my own yohgurt, so can you recommend a good probiotic one to purchase. My father had alzeiheimers and if I can help my own brain to hopefully stay healthy I am all for it.

    Many thanks.

    • Hi Susan – good question. I’d visit a good health food shop (not sure what is round in ChCh these days??) and ask there. I use Inner Health Plus from Ethical Nutrients – I assume you can get them in NZ as well as Australia. There are also a few ways you can make non-dairy probiotics…. I have a lovely friend Martha who has recipes for doing this yourself –

  4. Gut health affects mind and body. I have been making my own milk kefir and have never looked back. Never seem to get sick anymore. Nature provides what artificial drugs never can.

    • Hi Barbara – would you like to share your milk kefir recipe? I bet some of my readers have no idea what it is!

  5. Hi ,
    I love reading your articles .
    I have been fighting Candida for awhile in my body an dr’s don’t listen or dont seem to care or understand this infection. I so need to alleviate this problem anyway do you believe that candida in you gut an body could cause strokes an seizures ?
    What type if yogurt do you recommend if store bought ?

    • Hi Libbi – I can’t comment on whether candida can cause seizures. As far as I understand – diagnosed candida infections are treated with anti-fungals – you’d need to get a diagnosis first and then see how to go about treatment. That said, if you speak with CAM practitioners, the term ‘candida’ does cover a set of symptoms and they may have a different approach.

      In so far as store bought yogurts… you can’t go far wrong with unsweetened greek yogurt.

  6. Hi Sarah! Love to read what you have to say! Your knowledge helps me help my yoga students as well as my senior fitness and balance students! So, thank you to you and all of these inquiring minds that are interested in health and are willing to contribute!

    Please, would you be willing to provide your yogurt recipe as well as a good kefir recipe? Namasté

  7. Hi Sarah,

    I enjoyed reading your article which reinforced my own views on the benefits of a healthy diet.

    I am lucky to benefit from a local London market where there are organic and ethical producers of food.

    Yesterday, Hook & Son passed me details of their web site with the milk I purchased. This was the next web site I visited after reading your item and found this article:

    My life seems full of little coincidences like this at the moment.

    How many dairy producers do you know that have an awareness of neuroscience?

    I asked how long the milk would stay good and was advised that as it is raw it would not go bad and that when it turned “sour” I had the option to make yogurt or if I left it longer to separate I could make cheese.

    You cannot do that with supermarket milk.

    I hope anyone visiting the Hook & Son’s web site will be inspired by what they read to consider finding a source like this for their dairy needs (and gut / brain health).

    Thank you for your continued support and guidance.

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