Diet is key to healthy living but, strangely enough, the topic rarely comes up in conversations about mental health. Instead, we tend to focus on medication and therapy, and largely ignore the food that we eat – which, according to psychologist Kimberley Wilson, is a huge mistake. 

After working at what was once Europe’s largest women’s prison, HM Prison Holloway in London, she became keenly aware of the powerful influence diet has on mental wellbeing. She saw how, deprived of a balanced diet and nutrients, it was so much harder for prisoners to control their emotions. And she realised that proper nutrition is just as important for managing mental health as medication and therapy. 

She spoke with about why nutrition is the foundation of brain health and how the foods we eat can treat mental illness. 

Olivia Goldhill: How does nutrition influence brain health? I think most people understand that food is important for our bodies but are less familiar with its influence on our minds. 

Kimberley Wilson: Mental health is an emergent property of a physical organ. In the same way that your heartbeat is an emergent property of your heart, all of these things that we think about as mental wellbeing are an emergent property of your brain. If we want a coherent psychological experience, we should be thinking about the physical health and structural integrity of the brain as our starting point – and nutrition changes our brain’s ability to process thoughts and emotions, just like it influences the health of any other organ.

Why do you think we so rarely consider this mind-body connection?   

I think it is Cartesian. Four hundred years ago, René Descartes made the argument that there is an essence of the self that is separate from and superior to the physical body. It created such an impression on medicine and then psychiatry that we started approaching mental health as a neck-up intervention – the rest of the body is completely irrelevant.

The brain is also out of sight. Weightlifting changes your body very quickly, often within a few weeks. But because you can’t physically see changes to your diet, exercise and sleep in your brain, you have to wait for a subjective shift that can take six months.  

There is also a bit of egocentrism. We think of ourselves as deeply complex individuals. We don’t like the idea that malaise might be improved by a change of diet and a good night’s sleep. We seek either a complex pharmacological compound or a deep-probing-type therapy to get to our core complexities.  

Obviously, I provide some of that, too. But we also know that profound changes can be made with nutritional and lifestyle interventions. I see that in some prisons, where randomised controlled trials showed that changes in nutrition reduced violence. That is some of the starkest, clearest evidence that the brain is a physical organ, and if you want it to function well, you need to feed it properly.  

You worked in Holloway prison and young offenders institute up until 2013 – it is now closed, but was then the largest women’s prison in Europe. I imagine your experience there shaped your approach to mental health.

In prison, you are working with a very  traumatised and traumatising population. The focus is on the emergent behaviours – this person is angry, they are aggressive, they are dangerous, they are frightening – and most people aren’t thinking about the machinery from which those behaviours are emerging. 

But we are dealing with a group of people who have experienced extreme deprivation on all levels: emotional neglect, often abuse, but also severe nutritional, and often substance-related, harms to the brain.  

We have a justice system predicated on volition: you know right from wrong, and if you choose to do the wrong thing, then you deserve the consequences. But that is based on the assumption that the decision-making machinery is working properly. 

This is where we get into almost philosophical grounds with prison violence. If I get into a car and crash, and I didn’t know the brakes were shot, am I entirely responsible for the accident? Or are there mitigating circumstances that need to be taken into consideration? 

In terms of brain health and prison violence, we see that when you improve nutrition, violence drops by 30 per cent. These were supplement trials of broad-spectrum micronutrients, so vitamins, minerals and, in some cases, omega-3. 

Nobody wants to let people off scot-free, but I think we need to be thoughtful about the assumptions we make about behaviour, not just in prison, but across the board. 

Speaking more generally, what impact do physical health and diet have on our mental wellbeing? 

There is lots of evidence around the physical health of either the whole body or the brain impacting mental health. We have good data showing that 1 gram per day of omega-3 – where 60 per cent is EPA [a fatty acid found in omega-3] – can reduce depression. It is thought that inflammation drives depressive symptoms for some people. Omega-3s are the necessary precursors of inflammation’s “off switch”. 

Then there is data looking at brain trajectories and psychopathology. Brain scans have shown us that if the brain was smaller than expected in the prefrontal and parietal lobes, which manage higher-level thinking, that was associated with increased risk of psychopathology. We are talking about the physical structure of the brain as a risk factor.

Iodine deficiency in the perinatal period and early infancy, according to the World Health Organization, is the leading cause of preventable brain damage worldwide and is associated with low IQ. 

Some of the most robust data on depression prevention is around exercise. But we rarely think about this because [most people] think that mental health needs to be addressed with either psychotherapy or drugs. 

Traditionally, psychiatrists and psychologists are very brain-focused, but your approach to the brain seems to be more holistic. 

Yes, and I think the old-school psychiatric approach of using drugs to alter brain chemicals is just a tiny piece of the conversation. These compounds – serotonin or dopamine – are important for regulating mood, but they are also made from nutrients. 

If you are anaemic, you aren’t going to have good serotonin production because the brain needs iron for this process, and we see associations between iron deficiency and mood disorders like depression. One of the simplest fixes for a mood disorder is to check, are you anaemic? If so, we can correct this with either diet or iron supplementation. Then, we have improved your fatigue, your flatness of affect, and you haven’t had to go to therapy for six months. 

How do you think data on nutrition and mental health should inform diagnosis and treatment? 

What needs to happen is a better assessment process. Rather than a binary “are you depressed, are you not”, what we want to ask is, what is driving your depression? Is it your childhood trauma, in which case, let’s fast-track you to in-depth therapy. Is it relationship stress? Is it workplace demands? Is it that you have eaten only two chocolate muffins in the last four days? That isn’t going to help you feel good. If we intervene there first, then we can make a difference in the way that you feel very quickly.  

So, if you lived off only ultra-processed foods, for example, what would happen to the brain?  

The brain is the hungriest organ in the body. We need to supply it with the nutrients it requires so that we can feel good, focus, have goal-directed behaviour – all of that stuff.  

A single doughnut isn’t going to meaningfully hurt your brain. But the more your diet is made of these foods, the lower your nutrient status. You will be lower on things like [vitamin] B3 and B12, omega-3, selenium and zinc. That is a problem, because your brain is then depleted of the things it needs to function well.  

We’ve talked about the nutritional effects of diet on the brain, but I’m also curious about the sociological importance of eating. Are there health benefits to sharing our meals with others?

I think so. I think cooking and eating together is part of what makes us human. Across human evolution, eating together was a necessity, because you couldn’t go out and hunt and gather for yourself. It was a group process: I share what I have, and you share what you have.  

There is lovely data on how we feel more trusting of people when we eat together, and it’s not simply that you eat with people you already trust. There is something about eating that builds those relationships, and I think that has to do with the physiology of eating. You have your fight and flight, and then you have your rest and digest. You need to be calm, you need to feel safe [and] you need to feel like you are with people who are trustworthy, so that you can drop your guard and digest your food. 

You just had a baby. How has pregnancy and the postpartum period influenced your understanding of the importance of nutrition, if at all?  

I took the position that I am building a brand-new brain from scratch. So, it was important for me to think about what I am supplying that brain with in order for it to develop optimally.

I was comparing prenatal supplements with research on what nutrients are important for brain development and just finding them massively wanting. Basically, no prenatal vitamin has enough of the nutrient choline, simply because choline salts are bulky. Though we know that choline can do the same thing that folic acid does in reducing the risk of neurological congenital conditions, and we see that choline supplementation during pregnancy improves attention in children at age 7. 

I am breastfeeding, and those nutrients become present in your breast milk. So, I take a choline supplement, to make sure that I am getting enough for my son. 

Is there one nutritional change for mental wellbeing that you think most people could benefit from? 

I would probably say increasing your intake of omega-3 – ideally by eating at least one portion of oily fish a week, and vegans or vegetarians may want to take a supplement. That is where some of the strongest data is, showing reduced risk of depression and suicidal ideation, we think as a function of reduced neuroinflammation. Given that hardly anybody in the UK is getting enough fish, we can assume that a good number of people would be helped by just making that one change.  

Do you think we will see change in how people talk about diet and mental health? 

When I first started talking about this research, I was speaking to a colleague and he just laughed at me. It was quite disappointing, and he just said, well, I have never heard of it. 

It’s hard to tell if things are getting better because I don’t know whether I’m now in a bit of a bubble. I hope the old approach is being pushed out by more open-minded, grounded-in-the-new-research, optimistic individuals saying, actually, the brain is a physical organ and there is something we can do to improve mental health.