‘Physical and mental health support must go hand-in-hand if we’re to truly improve outcomes’

Writing as a medical doctor, how has your book been received by Psychologists? I mean, more widely than winning the British Psychological Society's Book Award!

It's been immensely gratifying, and somewhat surprising, to see the book really resonate with psychologists. While I expected interest from the medical community, the enthusiastic response from all psy- disciplines suggests a real hunger for integrating biological and psychological perspectives. The BPS Book Award was a huge honour, but what excites me most is the possibility of the book helping to break down historical disciplinary silos.

You write 'join me in hammering the last nail in the coffin of mind-body dualism'… but do you think the coffin was at least mostly closed already? Although you do also write of 'a world that still unthinkingly treats mind and body as unrelated'. 

Yes and no. In the academic world, dualism has largely been abandoned, but culturally and clinically, it lingers. The continued separation of 'mental' and 'physical' health in medicine and daily language shows that this kind of thinking still shapes how we approach illness. I don't want to throw the baby out with the bathwater; often a mental-physical distinction can be useful in categorising the complexities of human existence. The issue arises when cultural forces, from medical systems to social stigma, lead people to believe that their long term illness is only physical or mental, thereby depriving themselves of tools to help them live well with – or even completely recover from – said illness.

Do you feel that the centrality of 'sickness behaviour' has been underplayed by Psychologists? Given that, as you say, 'most of the real-world symptoms of immune activation involve mood and motivation'.

This is a great question. I certainly can't speak for most psychologists, but it's certainly true that although sickness behaviour is a striking example of the immune system shaping psychology, it's often overlooked in psychological models of mood and motivation. This is definitely changing, however, through the pioneering work of psychology researchers such as Mats Lekander in Stockholm. I think one hugely important area is exploring how the psychological symptoms of sickness behaviour – lethargy, anhedonia, low mood, and cognitive slowing – can remain 'stuck' well after infection and inflammation has died down.

I love a zombie… talk to me about our 'collective primal fear of the infected'. 

Our fear of infection is deeply ingrained and often operates beneath conscious awareness. Studies show that people can detect sickness just by looking at subtle facial changes or even observing how someone walks – infected individuals take shorter, slower steps with reduced arm movement. Maybe this is where our stereotypical zombie comes from. Our sense of smell also plays a role; individuals injected with an inflammatory molecule produce odours that others rate as less pleasant. Seeing sickness in others doesn't just trigger disgust – it can actually prime our own immune system, raising body temperature and increasing inflammatory markers. What's also fascinating is the research exploring this instinct's darker side, suggesting that our 'behavioural immune system' and disease fears can fuel prejudice, xenophobia, and extreme social conformity.

What finding / study surprised you most in writing the book? For me, it's pretty incredible that the immune mind could kill us – the Ader and Cohen research with rats.

Oh I couldn't choose just one! But yes, Ader and Cohen's discovery that the immune system can be conditioned in the same way as Pavlov's dogs is pretty mind blowing; the thought of rats being trained to suppress their own immune response to the point of death. I think this is one study among many that made me realise that your mind and immune system are two parts of the same system – an anticipatory, predictive 'defence system' that responds to both physical and perceived threats. If we can identify when and how this system becomes miscalibrated, we should be able to approach mental and physical health in a new way, intervening more effectively with targeted therapies and behavioural interventions.

How robust do you think findings in some of these areas are? And do you think any scepticism over them speaks to a longstanding difficulty in getting our heads around the mind-body relationship?

Scepticism is healthy, particularly in emerging and complex fields. The gut microbiome, immune system, and human mind are three of the most complicated things in nature, so working out how they interact with each other is immensely difficult. The challenge is to work out whether the interactions seen in small experiments or animal models are actually clinically relevant on individual and population levels. We're making progress – the triangulation we have from many different studies suggests that there are signals in the noise – but are certainly not there yet. 

That must be such a challenge in writing a popular science book.

Yes. Of course, non-fiction books need to avoid bad science, but all papers have limitations and their findings need to be used in the wider context. For example, when I write about new research around cortisol levels in long covid, its methodology and applicability could certainty be criticised, but I include it in the context of cortisol changes being consistently observed in both depression and inflammation, and that these preliminary studies should inspire larger, more robust analyses. It's a fine balance in emerging fields, when the signal to noise ratio of studies is often low. It's important to find a path between both uncritically overhyping findings and dismissing them out of hand due to imperfect methodology – an intellectualising defence mechanism I see a lot amongst some academics, sometimes including myself!

Which of the emerging areas do you think holds the most promise for further improvements in how we harness the power of the immune mind? 

The theory of 'predictive processing' is particularly compelling – the idea that the brain constantly generates expectations about the world, including the state of the body and immune system. If inflammation biases this system towards interpreting the world as more threatening or negative, it could explain why inflammation and depression are so intertwined, and perhaps how symptoms can linger long after inflammation has receded. This could open up new treatment avenues beyond anti-inflammatories, using psychological approaches to rewire inflammatory biases. This also links to very exciting cutting-edge research – mainly limited to animal models at the moment – showing how the brain can activate specific immune responses in organs all over the body. 

The research around inflammation makes total sense to me. If I had to use one word to describe how I've felt at my worst, particularly over the last five years, it would be 'inflamed'. You write: 'Perhaps we are not that far away from a future in which you present to your GP with symptoms of depression, get a quick blood test…' Why aren't we already there / how do we get there?

We aren't yet there because while the link between inflammation and a sub-group of individuals with depression is well-established, translating that knowledge into clinical practice is far more complex. Neither depression nor inflammation are single, uniform processes, and the challenge lies in working out what works in whom. Personalised medicine is the key to making this clinically relevant. Studies have shown, for example, that anti-inflammatory medications don't seem to improve symptoms in a cohort of people with depression, but if you focus on those with elevated levels of blood inflammatory markers, and effect is seen. 

I'd like to return to mind-body dualism and its implications. This debate has played out for many, many years in our pages over areas such as mental health, but I do feel like most serious psychologists are now totally onboard with biopsychosocial. But then I read a bit of your book such as around anti-NMDA encephalitis, the immune system attacking the mind, and it scares me that those who still give unequal weight to the psycho and particularly the social would risk massively underdiagnosing that type of condition.

Yes, that's a real risk. The bottom line is you're only doing lip service to the biopsychosocial model if you are not properly assessing all three. It's comforting to try to stay in one's professional lane, but the truly rewarding work is interdisciplinary, even if that means knowing when to refer to another specialty for a different perspective. 

Perhaps relatedly, you write that 'The only harm in seeking targeted, expert-led psychological support is that it might receive the judgement of those on one side of the West's mind-body divide.' But my experience has been that with some issues, the concern from patients / advocates etc is that an emphasis on or availability of psychological support could slow or hinders the development of support from the 'other' side. Do you feel that's a valid concern?

I completely understand the concern. Access to psychological support should never come at the expense of proper screening and treatment for biological factors, just as focusing on biological interventions should never replace meaningful psychological care. More often than not people need both – physical and mental health support must go hand-in-hand if we're to truly improve outcomes. The reality on the ground – in the UK, at least – is unfortunately one of fragmented and unintegrated services. We need systemic change on conceptual, cultural, and financial levels. 

Like any great writer, you make heavy use of metaphor, but you encourage readers to pick which suits you best. Which suits you best? E.g. do you see yourself as a loop/ triangle / a community.

I think I gravitate towards the idea of a community – moving away from the notion of a mind piloting a body like an animatronic robot and instead seeing myself as an ecosystem of mind, cells, and microbiome. The immune system, brain, and microbes aren't separate entities but interconnected parts of a single, responsive network. This perspective fills me with a sense of awe and wonder, reminding me that evening when I'm not dining with other humans, I'm still sharing a meal with my microbes! More importantly, it reinforces the idea that physical and mental health are inseparable. When I'm feeling unwell – whether physically or emotionally – nurturing every aspect of this system is key to recovery.

I think that metaphors are a hugely important way of how we understand and act in our world. I'd like to conduct research exploring how best to communicate the bidirectional relationship between physical and mental health to patients and clinicians. It isn't straightforward (literally!) as we tend to prefer linear cause-and-effect narratives to understand health and illness. In many cases of chronic illness, this thinking is often to our detriment. 

I love how the final section of the book is around some fairly straightforward strategies to help yourself, including some underlying approaches to life. Which has had the biggest impact on you? The 'serenity prayer' is always a pretty good way to live! 

Yes, and I do also love the concept of 'tragic optimism' – recognising the reality of suffering yet still investing in hope. It's an antidote to the two poles of toxic positivity at one end and nihilistic despair at the others. I also like it as it helps train us to hold multiple truths and feelings at the same time. As well as the temptation to split the mind from the body, humans often tend to split the world (from other people to abstract concepts) into things that are either fully good or fully bad. This can give you short term certainty, but it often comes at the expense of truth, authenticity, health, and growth.

• Nominations for the British Psychological Society Book Award close on 22 June.