THE GUT - BRAIN AXIS
- liztherapydurham
- Aug 27
- 10 min read
Part of an ongoing series on science and pseudoscience in mental health
All posts in this series are reviewed prior to posting by an expert in the relevant field. Many thanks to Dr Viktoriya Nikolova at King's College London's Centre for Affective Disorders for taking the time to check that I have got things right and offering some helpful suggestions.
If my social media feed is to believed, my gut microbiome is solely responsible for my mood, my ADHD, my rather shonky immune system, my inconvenient cravings for a chip butty and a pint, my lack of motivation, and probably for humanity’s continued failure to achieve world peace.
As someone who trained in philosophy before working is psychotherapeutic counselling, I am fascinated by the current preoccupation with the gut-brain axis. One reason for this is that it is a genuinely exciting area of science that holds some promise for understanding and treating various conditions in the future. Another reason is that it reveals how embodied our psyches really are. But one of its greatest fascinations for me is its capacity to breed pseudoscience faster than microorganisms reproduce in the human digestive tract.
There is some good science here, and dedicated researchers are constantly discovering new things about the connections between gut health and mental health. There is also a hell of a lot of questionable marketing, and some of it is basically people in lab coats with shiny hair and suspiciously perfect teeth shouting the word ‘microbiome’ while attempting to flog a £100 a month supplement subscription.
One of my aims in this series is to distinguish between what we know, what we suspect, and what people are confidently claiming without good evidence (usually in order to sell you something).
What is the Gut-Brain Axis?
The gut-brain axis refers to the various ways that the gut and brain constantly influence one another. This isn’t a bit of wellness woo: it is well-established biology. Scientists often describe these organs as ‘communicating’, ‘exchanging information’, or ‘sending signals’. I will echo this language of information and communication here, but we should be careful not to take it too literally.
Messages between the brain and gut travel in both directions through several pathways, including:
the vagus nerve (we will meet this character many times in this series!)
hormones
the immune system
chemical compounds produced by gut microbes
the enteric nervous system (sometimes called the ‘second brain’)
This occurs all the time, but it will have become especially noticeable if you've ever had ‘butterflies in your stomach’ before an exam or lost your appetite during a stressful week. Equally, anyone living with a chronic digestive condition will know that symptoms can affect mood, energy and quality of life. The gut and brain genuinely influence one another.
The language of ‘communication’ between organs, using ‘signals’ to convey ‘information’ is very common in biological science. It is a useful shorthand, but could be misleading if we take it too seriously. For example, nerves conduct electrical impulses, immune cells respond to chemical gradients, and gut bacteria produce metabolites. These are physical and biochemical processes, and not communication in the same sense as when we send a strongly worded complaint to the council or make awkward small talk at parties. Calling this ‘communication’ captures the idea that changes in one system predictably lead to changes in another, and not that bodily organs have intentions or consciousness.
Pseudoscience sometimes has a tendency to take scientific metaphors literally. I will talk about this more in other posts in this series.
What does the science tell us?
Researchers have found that people with conditions such as depression and anxiety often have gut microbiomes that differ, on average, from those of people without these conditions (Cao et al., 2025; Cheung et al., 2019; Barandouzi et al., 2020). This does not mean that there is a characteristic ‘depressed gut’, but that on a population level, the averages look different.
That immediately raises a difficult question: did changes in the microbiome cause the mental health condition?
Some wellness influencers would have you believe that this research supports the idea that our depression is the consequence of our personal failures to cultivate our inner microbiotic menageries, and that we can magically heal depression and anxiety with a weird powder that you add to a smoothie.
But there is another possibility. If you have ever experienced anxiety or depression, you will know that this can disrupt your diet, your sleep patterns, your stress levels, and your activity. All of these can affect the gut microbiome. You may also be taking medication that alters your gut microbiome (many antidepressants have gut issues among the side-effects - perhaps a small price to pay depending on the benefits). Furthermore, depression and anxiety are common among neurodivergent people, many of whom have sensory issues that affect their diets.
More evidence is needed to be clear on the directions of causation , but it is likely that, like most things in biology, this is not a one-way street: the least surprising explanation for these results would be that gut microbiome affects mental health and also vice-versa. We are gloriously complicated beings, which makes us bloody awkward to study.
What about probiotics?
Some studies suggest that particular probiotic strains may produce small improvements in mood or anxiety for some people. This is an active area of research, and it deserves to be taken seriously.
But, and it’s a big but (I cannot lie), findings have been inconsistent, and very few strains have been reliably replicated across large, high-quality studies. Different studies use different bacterial strains, different doses and different participant groups, making results difficult to compare. Effects, where they occur, tend to be modest (although larger in clinical populations than the general population).
There is genuinely exciting and promising research in this area. All the same, nobody can claim, on the basis of current science, to have developed ‘a probiotic for depression’.
Where does the pseudoscience come in?
Pseudoscience often starts with a real scientific finding and then stretches it far beyond what the evidence supports.
For example, they might start with the supported claim that the gut and brain communicate, and conclude from this the unsupported claim that anxiety is caused by an unhealthy gut. Or they might take the promising evidence that gut bacteria has some influence on mental health, and conclude from this the (unsupported) claim that a microbiome test can diagnose the cause of your depression, or that an expensive supplement will ‘repair your gut-brain axis’.
Short philosophical confession: philosophers of science don’t agree on a single definition of pseudoscience, largely because they don’t agree on a single definition of science. There is no universally accepted test that separates one from the other. When I use the term ‘pseudoscience’ in this series, I am not talking about ideas that fail to meet some carefully delineated criteria, but claims that present themselves as scientific while overstating, misrepresenting, inventing, or ignoring the available evidence. Some of my philosophical pals might prefer to speak in terms of ‘epistemic vice’
In all these cases, you can see a consistent pattern: the science gets less nuanced and shouty as the marketing message gets louder.
And if anyone starts telling you that transplanting someone else’s poo into your intestines will ‘cure’ your autism, RUN AWAY!
A cautionary tale about reductionism
The gut-brain axis Is one example of a recurring problem in mental health science. For a very long time, the dominant narrative about depression was that it was a ‘chemical imbalance in the brain’. This has been very helpful to some sufferers, as it made it clear that their condition was not their fault, and often beyond their control. There is no more shame in a chemically unbalanced brain than there is in acid reflux or type 1 diabetes.
However, the ‘chemical imbalance’ idea proved to be a considerable oversimplification. Brain chemistry matters, but it is only one part of an enormously complex picture involving genetics, development, psychology, relationships, life events, social circumstances and physical health. One of my biggest concerns about the chemical imbalance story is that it neglects the connection between depression and poverty, health inequality, and oppression.
With the rise of gut-brain axis talk, there is a risk that we replace one reductionist story with another: instead of saying, ‘Depression is caused by a chemical imbalance’, we start saying, ‘Depression is caused by an unhealthy microbiome’. Mental illness doesn't come about in a simple unifactorial way. It emerges from a tangled web of biological, psychological and social processes.
What does this mean for therapists?
Although posts in this series are checked over by relevant scientists, I am not a scientist, and nor are most counsellors and psychotherapists. We do not have detailed knowledge of microbiology, and nor do we need to. However, we do need to avoid simplistic stories.
There can be a temptation for therapists to put every aspect of mental health down to past trauma, or unhelpful thought patterns, or whatever factor or factors we typically work with: to a hammer, every problem looks like a nail. But we should not dismiss a client’s concerns when they tell us they've read about the gut-brain axis. The gut and brain really are connected, and physical health can have profound effects on emotional wellbeing.
The flipside of the coin is to be overly seduced by current wellness trends, and this is also not unusual in therapeutic circles. We should be cautious about suggesting that changing a client's diet or taking a probiotic is likely to resolve complex psychological difficulties. We are rarely in a position to know whether someone's gut health is contributing to their distress, and it is outside most therapists' scope of practice to diagnose or treat gastrointestinal conditions.
Instead, the gut-brain axis reminds us to focus on the whole person as an embodied, feeling and thinking being. Psychological distress affects the body, and physical health affects psychological wellbeing. Neither should be ignored.
As with any persistent physical symptoms, therapists should encourage clients with long-lasting digestive symptoms (more than a couple of weeks) to seek appropriate medical advice. Sometimes gastrointestinal symptoms are primarily stress-related, but they reflect a medical condition that deserves investigation (which may even be contributing to their psychological symptoms). It isn't our role to decide which.
Above all, we should resist the temptation to replace one oversimplified explanation with another. A client's difficulties are unlikely to be fully explained by their childhood, their thoughts, their neurotransmitters, or their gut microbiome.
What is Good Advice?
It's important to distinguish here between supporting health and treating mental illness. There is no diet, probiotic or supplement that has been shown to treat depression, or anxiety, or indeed to ‘cure’ ADHD or autism. If someone tells you otherwise, they are claiming more than the evidence supports. At best they are mistaken, and at worst they are being exploitative and offensive.
However, some everyday habits appear to support both physical and mental health for many people. Since the gut and the brain are in constant two-way communication, it makes sense that we would attend to our mental health and gut health at the same time, as each influences the other.
These everyday habits are, I’m afraid, pretty boring and mundane, and sadly do not include a chip butty and a pint as a positive recommendation. If it is realistic and appropriate for you, you might consider whether you are:
including a range of fibre-containing foods over time, where these are tolerated
eating a varied diet rich in fruit, vegetables and wholegrains
eating regularly enough to meet your body's needs
moving your body in ways that you enjoy or can comfortably manage
prioritising sleep where possible
maintaining supportive relationships
seeking evidence-based psychological or medical care when you need it.
Notice that I said ‘if it is realistic and appropriate for you’, and focused this on adapting these things to your needs and circumstances. Many people cannot simply decide to eat a wider variety of foods.
If you have an eating disorder, are recovering from one, or suspect you might have one, nutritional changes should ideally happen with support from appropriately qualified professionals. Restricting foods in pursuit of a ‘perfect microbiome’ has the potential to reinforce disordered eating rather than improve health, and this is a further concern I have about this and other areas of ‘wellness’ culture.
Similarly, many autistic people and ADHDers have sensory sensitivities, interoceptive differences, executive functioning challenges or restricted eating patterns. People who tell us to ‘just eat more vegetables’ or ‘simply increase your fibre intake’ are infuriatingly unrealistic, and may be distressing. Supporting nutrition may mean working with safe foods first, making gradual changes where possible, or recognising that other aspects of health deserve attention too.
People living with IBS, inflammatory bowel disease, coeliac disease or other gastrointestinal conditions may also need tailored advice rather than general recommendations, especially where dietary fibre exacerbates symptoms.
Main Points to Take Away
The gut-brain axis is real.
It is likely that the microbiome plays a role in mental health.
Researchers are making exciting discoveries.
But it is doubtful that we will ever be able to explain or treat most mental health conditions by analysing someone's gut bacteria, and if we will, that is a long way off.
Perhaps the most useful message from gut-brain research is that our minds and bodies are deeply interconnected. Looking after one is often a way of looking after the other.
Questions to ask when considering a gut-brain claim:
Is this describing a genuine scientific finding?
Does it acknowledge uncertainty, or claim certainty where the science is still developing?
Is it talking about one contributing factor, or pretending to have found the cause of mental illness?
Is there good evidence that the proposed treatment actually improves mental health, or only that it changes the microbiome?
A small but important note: I’m a psychotherapeutic counsellor with an enthusiasm for science, not a doctor, dietitian or gastroenterologist. This post is intended as general information, not personalised medical or nutritional advice. Bodies are complicated, inconveniently individual things, so if you’re worried about your physical or mental health, please seek advice from an appropriately qualified professional rather than a blog post on the internet.
I am currently accepting new clients for psychotherapeutic counselling, in person in Durham and online throughout the UK. I work with adults facing a range of difficulties, with particular experience in neurodivergence, stress and burnout, chronic health conditions, and the complicated ways our physical and psychological lives intersect.
Contact me
References:
Barandouzi, Z.A. et al. (2020) ‘Altered composition of gut microbiota in depression: a systematic review’, Frontiers in Psychiatry, 11, 541. Read the paper
Cao, Y. et al. (2025) ‘Gut microbiota variations in depression and anxiety: a systematic review’, BMC Psychiatry, 25, 443. Read the paper
Cheung, S.G. et al. (2019) ‘Systematic review of gut microbiota and major depression’, Frontiers in Psychiatry, 10, 34. Read the paper
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