We have long recognised that the brain influences the gut – just think of how stress can play havoc on your bowels – but we are now appreciating it is a two-way street, and that the health of your gut can profoundly alter the health of your brain.
One of the key components of this so-called gut-brain axis is the microbiome – the collection of microorganisms that live in your gut.
In total, this population of bacteria, viruses and fungi can weight a mighty 2kg, and consists of up to a mind-boggling 100 trillion individual creatures.
Although research is still very much in its infancy, we know that the microbiome can act as friend or foe. If there are too many of the wrong kind of bacteria, this leads to a condition called dysbiosis, which in turn creates chronic inflammation.
This inflamed state may involve the brain, leading to its immune cells becoming activated as it tries to address the problem. Many experts now believe that it is the attempt to tackle the inflammation that leads to the death of brain cells, and hence dementia.
One of the most compelling studies to illustrate this was performed on mice, whose mouths (technically part of the gut) were filled with a bacterium called p gingivalis.
For those of who have had your coffee, you may recognise that the similarity with another word – gingivitis – or inflammation of the gums, and this is no coincidence, as p gingivalis is a very common cause of gum disease and poor oral health.
When the mice were deliberately given this bacterium, their brain created more beta-amyloid, one of the proteins implicated in Alzheimer’s Disease.
This has been supposed to be because amyloid has an anti-microbial action – it is released to contain the infection. In addition, the toxin released by p gingivalis affected the other Alzheimer’s protein – tau.
So, in this instance, the microbiome acts as an enemy (another reason to brush your teeth and floss!), but how can they be helpful?
Again, this needs a lot more study, but one mechanism is through the way the gut bacteria process what you eat.
In particular, some healthful bugs have the ability to produce short-chain fatty acids (SCFAs for short – a well-known example is butyrate) from your food.
It seems these compounds are very beneficial for your brain, helping communication between nerve cells, promoting a healthy blood brain barrier, which is critical for good brain function, and consolidating memory.
There is a long list of things you can do to nurture the right gut bugs, including avoiding unnecessary antibiotics and excessive alcohol, and exercising regularly.
Social contact is also helpful – literally sharing bugs with others that you might hug or touch may increase their diversity – and some research shows that owning a dog can help, probably for the same reasons.
And then there’s your diet. Eating a broad range of healthy foods is recommended – different bacteria thrive on different nutrients – as is avoiding too much saturated fat, sugar, and processed food.
Your microbiome loves fibre as well and so try to get enough roughage. Finally, fermented foods and drinks like sauerkraut, kombucha, kimchi and kefir are like rocket fuel for the good bacteria and are seriously worth considering.
With fibre and fermented foods, if you are not used to eating them, build up gradually. If you run into problems or want more tailored advice, dieticians are worth their weight in gold.
Kailas Roberts is a psychogeriatrician and author of Mind your brain The Essential Australian Guide to Dementia now available at all good bookstores and online. Visit yourbraininmind.com or