We know it, and science agrees –‘Intuition’ or ‘gut-instinct’ is a useful tool in complex decision-making and as women, we are flooded with waves of complex decisions every day of our lives. Sometimes we’re able to step back and take a reasoned, well-thought-out approach –but more often than not we’ll ‘go with our gut’.
What we used to call ‘gut instinct’ now has a fancy, sciency name too –The Gut-Brain Axis. It turns out that what’s happening in our gut quite literally effects our moods, decision making and even our long-term mental health.
If you’ve ever had ‘one-too-many’ (and who hasn’t?) you’ve already felt the very real physical and mental effects of a neurotoxin at work on your body and mind. Good old ethyl alcohol in sufficient quantities can substantially alter your behaviour, mood, language and judgement can’t it? Its effects are often felt most strongly the next morning too. A hangover is partially massive dehydration and partially the after-effects of the neurotoxin you just ingested.
Of course, alcohol consumption is a choice. We know what it’s likely to do to us, and we blithely ignore the less convenient bits like the inevitable hangover. It stands to reason then that alcohol isn’t the only thing we ingest that is likely to affect our brains. This isn’t exactly ‘news’ to most of us either. We know that chocolate stimulates the release of ‘happiness hormones’ for instance, and that a cup of chamomile tea will soothe and relax.
Now, unless you’ve been living under a rock –you’ve probably also heard of the gut microbiome. For those that haven’t, the phrase refers to the fact that the human gastro-intestinal tract is home to about 10^ 14 microorganisms. Yes, they’re little –but they’re alive and there’s an awful lot of them. The fact that they’re living creatures means that they eat and excrete. What they eat is what you eat, and what you eat appeals to some more than others (there’s quite a variety of species down there!).
A ‘normal’ microbiome is not really something that can be defined by the way, -it’s a bit like using BMI as a universal measurement –there will always be tonnes of exceptions because we’re a pretty genetically diverse lot. There are three ‘main’ species though; Bacteroides, Prevotella and Ruminococcus. If you eat a high-protein diet, you’re likely to have more Bacteroides whereas a high-carb diet will encourage the proliferation of Prevotella.Neither of those things is a particular problem. As long as there’s a balanced diversity down there, she’s apples.
The problem comes when one or two species out-compete others and an imbalance is created. In science-ese this is known as dysbiosis and it can have some pretty serious effects on physical and mental health. When our little microbes go to war and compete for available space, they have their own weapons –in this case short-chain fatty acids that harm other microbes, but also harm us. In short, their competitive belching produces small molecules that our immune system wants to get rid of. From there we get inflammation, a leaky gut-wall and a whole tonne of both microbes and by-products leaking into our blood stream and even crossing the blood-brain barrier. So, you get a hangover? –not quite. This isn’t a one-off assault of a large amount of neurotoxin. Gut dysbiosis can be present for years for starters (think – a ‘slow drip’), and is particularly important when you consider peak brain development years in the very young.
Anxiety and depression are two of the most studied microbiome/brain relationships, and the latest studies are starting to unravel the connection in detail. As it happens, the circuitry in your brain that deals with anxiety and fear runs between areas known as the amygdala and the prefrontal cortex.
Image from The Queensland Brain Institute, University of Queensland, Australia. https://qbi.uq.edu.au/brain-basics/memory/where-are-memories-stored
In mice without a microbiome (yes, there is such a thing –they’re known as ‘Germ-free’ mice) both the amygdala and the prefrontal cortex are highly abnormal. They’re physically different ( in science-land we call it abnormal morphology) and have massively reduced signalling power. Obviously, said mice also exhibit pretty definite signs of anxiety, fear and depression behaviours. Stop giggling, -yes, you can have a depressed mouse. No, we don’t send them to counsellors. Basically, their brains didn’t grow properly, and we now have an idea why. When the gut microbiome goes wrong, it actually has effects at the genetic level.
Image from Bipolar Network News bipolarnews.org/?tag-defeat-stress
The brains of these mice showed large numbers of miRNA molecules with altered expression levels, specifically the ones that control expression of a factor called BDNF (Brain-derived neurotrophic factor). You want this stuff. If you don’t have enough of it you have a very compromised lump of grey matter –and you guessed it –depression and anxiety. miRNA acts like the policeman of gene expression and translation. It actively stops certain areas of a gene from being translated into proteins. In situations of gut dysbiosis, the miRNA is behaving like a rogue cop. It is no longer a matter of ‘protect and serve’ so much as ‘smash the state’. 'No! This person does not need BDNF and a functioning, healthy brain...stop making that protein right now you ridiculous excuse of a ribosome!'(Note: For clarity's sake, I should mention that there is absolutely no evidence that miRNA speaks. Poetic license.)
The good news is that when germs (microbiome) are restored to these mice, we do see a partial reversal of the activity of these rogue miRNAs. The bad news is it’s not the majority of them.
Now, obviously there’s no such thing as a human being without a gut microbiome and so the effects of gut dysbiosis will be different in both effect and scale in the human brain. We also don’t yet know the exact mechanism at work here. What we do know is that the contents and health of our gut microbiome is likely to affect our brains even at a genetic level. It’s as good a reason as any to keep reaching for those healthy pre-biotic foods (fruits, vegetables, legumes) and to avoid ingesting our favourite neurotoxins too regularly.
